Diagnostic signs of chordates. chordate animals. Main classes, their characteristics. Habitat and distribution
Characteristics of the type and system. The chordate phylum is often referred to as the highest phylum of animals. This is not entirely accurate, since chordates crown only a branch of deuterostomes ( Deuterostomy), while the top of the protostomes branch ( Protostomia) occupy types: arthropods ( Arthropoda) and shellfish ( Mollusca). The development of both branches followed different paths and led to the development of fundamentally different, but biologically highly active and complex types of organization of living matter.
Type Existence Chordata was substantiated by the famous Russian zoologist A. O. Kovalevsky, who, studying the development (ontogenesis) of tunicates ( Tunicata) and non-cranial ( Acrania), established the fundamental similarity of their organization with vertebrates. The name of the chordate type was proposed by Ball in 1878. Now the chordate type is accepted in the following volume (extinct groups are marked with a cross (†).
The non-cranial and tunicate subtypes are usually called the lower chordates, contrasting them with the higher chordates - the vertebrate subtype.
The chordate type includes about 43 thousand modern species distributed throughout the globe: they inhabit the seas and oceans, rivers and lakes, continents and islands. The appearance of chordates is very diverse (fixed saccular ascidians, somewhat similar to worms, non-cranial, vertebrates of various appearance). The sizes are also different: from appendicularia a few millimeters long, small fish and frogs 2-3 cm long to giants - some whales, reaching 30 m in length and weighing up to 150 tons.
Despite the huge diversity, all representatives of the chordate type are characterized by common organizational features that are not found in representatives of other types:
1. The presence throughout life or at one of the phases of development of the dorsal string - the chord (chorda dorsalis), which plays the role of the internal axial skeleton. It has an etiodermal origin and is an elastic rod formed by highly vacuolated cells; the notochord is surrounded by a connective tissue sheath. In most vertebrates, in the course of individual development (ontogenesis), the notochord is replaced (displaced) by the vertebral column, which consists of individual vertebrae; the latter are formed in the connective tissue sheath of the chord.
2. The central nervous system has the shape of a tube, the inner cavity of which is called the neurocoel. The neural tube is ectodermal in origin and lies above the notochord. In vertebrates, it is clearly differentiated into two sections: the brain and spinal cord.
3. The anterior part of the digestive tube - the pharynx - is lined with gill openings that open outward and performs two functions: a section of the digestive tract and a respiratory organ. In aquatic vertebrates, specialized respiratory organs, the gills, develop on the partitions between the gill slits. In terrestrial vertebrates, gill slits form in embryos but soon close over; specific organs of air respiration - the lungs - develop as paired protrusions on the ventral side of the back of the pharynx. The digestive tract lies under the notochord.
4. The pulsating part of the circulatory system - the heart - is located on the ventral side of the body, under the chord and digestive tube.
In addition to these typical features, chordates have some features that are also found in other types.
1. By breaking through the wall of the gastrula, a secondary mouth is formed; in the region of the primary mouth (gastropore), an anus is formed. This feature combines chordates with hemi-chordates, echinoderms, chaetognaths and pogonophores into a group of deuterostomes - Deuterostomy, opposed to the group of protostomes - Protostomia, in which a mouth opening is formed at the site of the gastropore, and the anus is formed by breaking through the wall of the gastrula (all other types of animals, except sponges, intestinal and protozoa, belong to the protostomes).
2. In the process of embryonic development, a secondary body cavity is formed - the whole, but all deuterostomes, annelids, mollusks, arthropods, bryozoans and brachiopods also possess it.
3. The metameric or segmental arrangement of the main organ systems is especially pronounced in arthropods and many worms. Metamerism is also clearly expressed in chordates, but in adult terrestrial vertebrates it manifests itself only in the structure of the spinal column and some muscles, in the origin of the spinal nerves, and partly in the muscles of the abdominal wall.
4. Chordates, like most other multicellular animals, are characterized by bilateral (bilateral) symmetry: only one plane of symmetry can be drawn through the body, dividing it into two halves, which are mirror images of each other.
Thus, the chordate phylum unites deuterostomes, bilaterally symmetrical coelomic animals with metamerism, expressed mainly in the early stages of embryonic development. They have an internal skeleton in the form of a chord with a neural tube lying above it; and under the chord is the digestive tube. The anterior end of the latter - the pharynx - is pierced by gill slits that open outwards. The heart lies on the ventral side of the body under the digestive tube. In higher chordates, the notochord is replaced by the vertebral column; in terrestrial classes, the gill slits overgrow and new respiratory organs develop - the lungs.
Origin of chordates. Fossil remains of the ancestors of chordates have not been preserved. Therefore, it is necessary to judge the early stages of their evolution largely by indirect data: by comparing the structure of adult forms and a comparative study of embryonic development.
Ancestors of chordates were searched among various groups of animals, including among annelids. For example, it was proposed to consider some sedentary polychaetes (polychaete worms) like modern ones as the ancestors of chordates. Sabellidae And Serpulidae. It was assumed that these hypothetical ancestors of chordates switched to an active lifestyle, but began to move on the originally dorsal (dorsal) side of the body. The anal groove characteristic of these worms, stretching forward through the glandular field along the abdominal surface, could close, forming a neural tube connected by a neuro-intestinal canal with the intestinal tube, and glandular cells, having become part of the neural tube, provided neurosecretory function. nervous system. In this case, the connective tissue cord, which in some polychaetes lies in the thickness of the ventral muscles, could become the precursor of the notochord. The probability of such formation of the internal skeleton, it would seem, is confirmed by the formation of a cartilaginous gill skeleton in some modern polychaetes. The loss of polymeric segmentation (eg, enterophans) is a secondary phenomenon from this point of view (Engelbrecht, 1969).
These witty ideas have not been confirmed. Most zoologists believe that the predecessors of chordates were apparently coelomic worm-like animals that switched to a sedentary or sedentary lifestyle, which led to a decrease in the number of segments of their body (probably up to three) and the formation of a secondary mouth. They fed passively by filtering the water. These oligomeric inhabitants of the seabed, evolving, gave rise to four types. Among them, echinoderms, having formed a water-vascular ambulacral system and a complex apparatus for capturing food, gained the ability to move on different soils and switched to active feeding on immobile and inactive food objects. This ensured their biological success: in many biocenoses of the seabed, not only in shallow waters, but also at great depths, echinoderms flourish without serious competitors.
Pogonophores- a peculiar group of sedentary animals, now distinguished as a special type (A.V. Ivanov, 1955), continues to cause controversy regarding their origin and position in the system. Pogonophores sit in protective tubes and are distinguished by a very simplified structure: a central nervous system from the dorsal trunk with a head ganglion, the absence of organs of movement and a digestive tube. They live on nutrients dissolved in the water - decomposition products of the "rain of corpses" descending from the life-rich layers of water lying above. They are characterized by the so-called extraintestinal digestion: absorption is carried out by the cells of the tentacles. Such passive feeding is possible and expedient in the weakly moving water of the ocean depths.
The third branch of development led to the isolation of chordates. Apparently, at the very beginning of evolution, a small group of hemichordate animals separated from it at the present time, which is now given the rank of type. Type hemichordates ( Hemichordata) includes two classes: pinnatibranchs ( Pterobranchia) and enteric ( Enteropneusta). Representatives of both classes have a three-segmented body, consisting of a head lobe (proboscis), a collar and a trunk.
pinnatibranch- sedentary animals forming colonies in the form of bushes; in the cavities of the tubules (twigs of the bush) animals - zooids sit. The small hollow head lobe (proboscis) of the zooid has muscular walls and communicates with the external environment by a small pore. Inside, at the base of the head lobe, there is a "heart" 1 and an excretory organ, and on its surface there is a glandular organ, the secret of which serves to build the walls of the tubules - the branches of the colony. The collar, which has its own internal cavity, frames the mouth opening and serves as a support for the branching tentacles - the respiratory and food collection organs. On the dorsal surface of the collar, a short chain of nerve ganglia is located intraepithelially, extending to the proboscis. The trunk is occupied by a curved intestinal tube.
Genus representatives Cephalodiscus And Atubaria in the upper part of the intestinal tube they have a pair of "gill" openings that open outward, which, however, are not related to breathing and serve only to discharge water during filtration. The collar with tentacles and the base of the proboscis are supported by the notochord, a small elastic outgrowth of the dorsal part of the intestine, which allows us to consider the notochord as the rudiment (predecessor) of the notochord. In the body cavity (coelom) are the sex glands, which open outwards with short ducts. From a fertilized egg, a mobile larva develops, capable of crawling and swimming, which soon sits on the bottom and after two days turns into an adult animal. The latter forms a new colony by budding. Kidneys are formed on the stolon, in the tail section of the body.
Enteric-breathing have an elongated worm-shaped body; length from a few centimeters to 2-2.5 m ( Batanoglossus gigas). They lead a solitary lifestyle, are quite mobile, live mainly in shallow sea waters, but are also found at depths up to 8100 m. In the ground, by mining, they make U-shaped mink passages. Their walls are held together by mucus secreted by glandular skin cells.
The proboscis has muscular walls; through a small hole, its cavity can be filled with water, turning the proboscis into a tool for making holes. There is also a small whole inside the collar. On the ventral side, between the proboscis and the collar, there is a mouth opening leading to the pharynx (Fig. 4). The walls of the pharynx are pierced by numerous paired gill slits that open outward on the dorsal side of the body; at the bottom of the pharynx in some species, a longitudinal thickening is formed, which can probably be considered as the rudiment of the endostyle. The pharynx passes into the intestine, ending with the anus at the posterior end of the body. Numerous blind hepatic outgrowths depart from the dorsal surface of the anterior part of the intestine; they are visible from the outside as rows of tubercles. At the base of the proboscis, as in pinnatibranchs, a small hollow elastic outgrowth of the pharyngeal wall protrudes, formed by vacuolized cells and strands of connective tissue, the notochord. In balanogloss, several muscular bands are connected with the notochord, going to the caudal part of the body. This can be seen as a prototype of that myochordial complex, with the development and improvement of which the progress of chordates is associated.
Circulatory system open. Two longitudinal vessels - dorsal and abdominal - are connected by transverse vessels passing through the partitions between the gill slits. The dorsal vessel opens into the head lacuna located above the notochord. Adjacent to it is the "heart" - a hollow muscular vesicle: its rhythmic contractions create a blood flow. A folded formation penetrated by blood vessels protrudes into the cavity of the proboscis, performing the function of an excretory organ; its epithelium is similar to that of the excretory organs of chordates. The decay products diffuse into the cavity of the proboscis and are brought out with water through the proboscis pore. Breathing is carried out both by the entire surface of the body and in the pharynx: oxygen enters the blood flowing through the vessels of the interbranch septa. The nervous system consists of dorsal and abdominal nerve cords connected by one or two parapharyngeal nerve rings (commissures). In the anterior part of the dorsal nerve cord there is usually a cavity similar to the neurocoel of the neural tube of chordates. The sense organs are represented by sensory epidermal cells, which are more numerous on the proboscis and the anterior part of the collar. Sensory cells scattered at the top of the proboscis are light sensitive.
Type Chordates combines animals that are very diverse in appearance, lifestyle and living conditions. Representatives of chordates are found in all the main environments of life: in water, on the land surface, in the thickness of the soil and, finally, in the air. They are geographically distributed throughout the world. The total number of species of modern chordates is approximately 40 thousand. The Chordata type includes non-cranial (lancelets), cyclostomes (lampreys and hagfish), fish, amphibians, reptiles, birds and mammals.
As shown by the brilliant studies of A. O. Kovalevsky, the chordates also include a peculiar group of marine, largely sessile, animals - tunicates (appendicularia, ascidians, salps). Some signs of similarity with chordates are found by a small group of marine animals - enteropneusta, which are sometimes also included in the chordate phylum.
Despite the exceptional diversity of chordates, they all have a number of common structural and developmental features. The main ones are:
1. All chordates have an axial skeleton, initially appearing in the form of a dorsal string, or chord. The notochord is an elastic, non-segmented strand that develops embryonically by lacing it from the dorsal wall of the germinal gut: the notochord is of endodermal origin. The subsequent fate of the chord is different. It persists for life only in lower chordates (with the exception of ascidia and salps). In most representatives, the notochord is reduced to one degree or another in connection with the development of the spinal column. In higher chordates, it is an embryonic organ and in adult animals it is to some extent displaced by the vertebrae, in connection with this, the axial skeleton becomes segmented from a continuous non-segmented cord. The spine, like all other skeletal formations (except the chord), is of mesodermal origin and is formed from a connective tissue sheath surrounding the chord and neural tube.
2. Above the axial skeleton is the central nervous system of chordates, represented by a hollow tube. The cavity of the neural tube is called the neurocoel. The tubular structure of the central nervous system is characteristic of almost all chordates. The only exceptions are adult tunicates. In almost all chordates, the anterior neural tube grows and forms the cerebrum. The internal cavity is preserved in this case in the form of the ventricles of the brain. Embryonally, the neural tube develops from the dorsal part of the ectodermal bud.
3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment with two rows of holes, called visceral fissures. In lower forms, gills are located on their walls. Gill slits are preserved for life only in lower aquatic chordates. For the rest, they appear only as embryonic formations, functioning at some stages of development or not functioning at all.
Along with the indicated three main features of chordates, the following characteristic features of their organization should be mentioned, which, however, besides chordates, representatives of some other groups also have. chordates, as well as
common features of the chordate type
- The chordate phylum is subdivided into three subtypes: non-cranial, tunicates, and vertebrates. Despite the great variety of species, the body of all chordates has a common structural plan and consists of a head, trunk, tail and limbs. The main feature of representatives of the type is the presence (at least at one of the stages of individual development) of a chord of a flexible, elastic cord, which acts as an axial skeleton. The notochord is located above the intestine and is formed from the endoderm by splitting off a cell cord from the dorsal side of the intestinal tube.
Despite the exceptional diversity of chordates, they all have a number of common structural and developmental features. The main ones are:
1. All chordates have an axial skeleton, which initially appears in the form of a dorsal string, or chord. The notochord is an elastic, non-segmented strand that develops embryonically by lacing it from the dorsal wall of the germinal gut: the notochord is of endodermal origin. The subsequent fate of the chord is different. It persists for life only in lower chordates (with the exception of ascidians and salps). In most representatives, the notochord is reduced to one degree or another in connection with the development of the spinal column. In higher chordates, it is an embryonic organ and in adult animals it is to some extent displaced by the vertebrae, in connection with this, the axial skeleton becomes segmented from a continuous non-segmented cord. The spine, like all other skeletal formations (except the notochord), is of mesodermal origin and is formed from a connective tissue sheath surrounding the notochord and neural tube.
2. Above the axial skeleton is the central nervous system of chordates, represented by a hollow tube. The cavity of the neural tube is called the neurocoel. The tubular structure of the central nervous system is characteristic of almost all chordates. The only exceptions are adult tunicates. In almost all chordates, the anterior neural tube grows and forms the brain. The internal cavity is preserved in this case in the form of the ventricles of the brain. Embryonally, the neural tube develops from the dorsal part of the ectodermal bud.
th. In lower forms, gills are located on their walls. Gill slits are preserved for life only in lower aquatic chordates. For the rest, they appear only as embryonic formations, functioning at some stages of development or not functioning at all.
Along with the indicated three main features of chordates, the following characteristic features of their organization should be mentioned, which, however, besides chordates, representatives of some other groups also have. Chordates, like echinoderms, have a secondary mouth. It is formed embryonically by breaking through the gastrula wall at the end opposite the gastropore. In place of the overgrown gastropore, an anus is formed. The body cavity in chordates is secondary (as a whole). This feature brings chordates closer to echinoderms and annelids.
The metameric arrangement of many organs is especially pronounced in embryos and lower chordates. In their higher representatives, due to the general complication of the structure, metamerism is weakly expressed.
Chordates are characterized by bilateral (bilateral) symmetry of the body. As is known, in addition to chordates, many groups of invertebrates have this feature.
Evolutionarily, chordates are characterized by morphophysiological continuity in all organ systems, which can be traced in the change in homologous organs.
- All chordates have an axial skeleton or notochord.
3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment by two rows of holes, called visceral slits - . All chordates have an axial skeleton or notochord.
2. Above the axial skeleton is the central nervous system of chordates, represented by a hollow tube. In almost all chordates, the anterior neural tube grows and forms the brain.
3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment by two rows of holes, called visceral slits - the presence of a chord instead of a spine. lack of bones
- Despite the huge diversity, all representatives of the Chordata type are characterized by common features of organization that are not found in representatives of other types. Consider the main features of the type using an interactive scheme:
The body is bilaterally symmetrical.
Intestine through.
Above the intestines is a notochord.
Above the chord, on the dorsal side of the body, is the nervous system in the form of a neural tube.
The walls of the pharynx have gill slits.
The circulatory system is closed. Heart on the ventral side of the body, under the alimentary canal.
They live in all environments.
The chordate type unites animals that are very diverse in appearance, lifestyle and living conditions. Representatives of chordates are found in all the main environments of life: in water, on the land surface, in the thickness of the soil and, finally, in the air. They are geographically distributed throughout the world. The total number of species of modern chordates is approximately 40 thousand.
The chordate type includes non-cranial (lancelets), cyclostomes (lampreys and hagfish), fish, amphibians, reptiles, birds and mammals. To chordates, as shown by the brilliant studies of A.O. Kovalevsky, also includes a peculiar group of marine, and to a large extent sessile animals - tunicates (appendicularia, ascidians, salps). Some signs of similarity with chordates are found by a small group of marine animals - intestinal-breathers, which are sometimes also included in the chordate phylum.
Despite the exceptional diversity of chordates, they all have a number of common structural and developmental features. The main ones are:
1. All chordates have an axial skeleton, which initially appears in the form of a dorsal string, or chord. The notochord is an elastic, non-segmented cord that develops embryonically by lacing it from the dorsal wall of the germinal gut. Thus, the notochord is of endodermal origin.
The subsequent fate of the chord is different. For life, it is preserved only in lower chordates (with the exception of ascidians and salya). However, in this case, in the majority, the notochord is reduced to one degree or another in connection with the development of the spinal column. In higher chordates, it is an embryonic organ and in adult animals it is to some extent displaced by vertebrae, in connection with this, the axial skeleton becomes segmented from a continuous, non-segmented one. The spine, like all other skeletal formations (except the notochord), is of mesodermal origin.
2. Above the axial skeleton is the central nervous system, represented by a hollow tube. The cavity of the neural tube is called the neurocoel. The tubular structure of the central nervous system is characteristic of almost all chordates. The only exceptions are adult tunicates.
In almost all chordates, the anterior neural tube grows and forms the brain. The internal cavity is preserved in this case in the form of the ventricles of the brain.
Embryonally, the neural tube develops from the dorsal part of the ectodermal bud.
3. The anterior (pharyngeal) section of the digestive tube communicates with the external environment with two rows of holes, called gill slits, since the lower forms have gills on their walls. Gill slits are preserved for life only in aquatic lower chordates. For the rest, they appear only as embryonic formations, functioning at some stages of development or not functioning at all.
Along with the indicated three main features of the chordates, the following characteristic features of their organization should be mentioned, which, however, besides the chordates, are also found in representatives of some other groups.
1. Chordates, like echinoderms, have a secondary mouth. It is formed by rupturing the wall of the gastrula at the end opposite the gastropore. In place of the overgrown gastropore, an anus is formed.
2. The body cavity in chordates is secondary (as a whole). This feature brings chordates closer to echinoderms and annelids.
3. The metameric arrangement of many organs is especially pronounced in embryos and lower chordates. In their higher representatives, metamerism is weakly expressed due to the general complication of the structure.
There is no external segmentation in chordates.
4. Bilateral (bilateral) symmetry of the body is characteristic of chordates. As is known, this feature, in addition to chordates, is possessed by some groups of invertebrates.
Class: mammals
general characteristics
Mammals are the most highly organized class of vertebrates. The main progressive features of mammals are as follows:
1) high development of the central nervous system, primarily the gray cortex of the cerebral hemispheres - the center of higher nervous activity. In this regard, the adaptive reactions of mammals to environmental conditions are very complex and perfect;
2) live birth and feeding of the young with the product of the mother's body - milk, which allows mammals to reproduce under extremely diverse living conditions;
3) a highly developed ability for thermoregulation, which determined the relative body temperature. This is caused, on the one hand, by the regulation of heat generation (by stimulating oxidative processes - the so-called chemical thermoregulation), on the other hand, by the regulation of heat transfer by changing the nature of the skin blood supply, etc. the forces of evaporation of water during breathing and sweating (the so-called physical thermoregulation.
Of great importance in regulating the release of heat is the coat, and in some, the subcutaneous fat layer.
These features, as well as a number of other features of organization, led to the possibility of a wide distribution of mammals in a wide variety of conditions. Geographically, they are distributed almost everywhere, with the exception of Antarctica. It is even more important to consider that mammals inhabit a wide variety of living environments. In addition to numerous terrestrial species, there are species flying, semi-aquatic, aquatic and, finally, inhabiting the soil. The total number of species of modern mammals is approximately 4.5 thousand.
Morphologically, mammals are characterized by the following features. The body is covered with hair (exceptions are rare and secondary). The skin is rich in glands. The mammary glands should be especially noted. The skull is articulated with the spine by two occipital condyles. The lower jaw consists only of the dentary. The quadrate and articular bones turn into auditory ossicles and are located V middle ear cavity. The teeth are differentiated into incisors, canines and molars: they sit in the alveoli ... The elbow joint is directed backward, the knee joint is forward, in contrast to the lower terrestrial vertebrates, in which both of these joints are directed laterally outward (Fig. 1) The heart is four-chambered, one left aortic arch is preserved . Erythrocytes are non-nuclear.
The structure of mammals
The skin (Fig. 1) in mammals has a more complex structure than in other vertebrates. Difficult and varied and its meaning. The entire system of the skin plays a huge role in the thermoregulation of mammals. The coat, and in aquatic species (whales, seals), the subcutaneous layer of fat protects the body from excessive heat loss. An extremely important role is played by the system of skin blood vessels. The diameter of their gaps is regulated by the neuroreflex pathway and can vary within very large limits. With the expansion of skin vessels, heat transfer increases sharply, with narrowing, on the contrary, it is greatly reduced.
Of great importance for the cooling of the body is also the evaporation from the surface of the skin of the water released by the flow glands.
Due to the described mechanisms, the body temperature of many mammals is relatively constant, and its difference from the ambient temperature can be approximately 100 0C. So, the arctic fox living in winter at temperatures up to -60 °С, body temperature is approximately +39 ° C. It should, however, be borne in mind that the constancy of body temperature (homeothermia) is not an absolute feature of all mammals. It is fully characteristic of placental animals, which are relatively large in size.
In lower mammals, which have a less developed thermoregulatory mechanism, and in small placental animals, which have a ratio between body volume and surface that is unfavorable for keeping warm, body temperature varies significantly depending on the ambient temperature (Fig. 3). So in a marsupial rat, the body temperature varies within + 37.8 ... + 29.3 ° C, in the most primitive insectivores (tenrecs) 4-34 ... 4-13 ° C, in one of the species of armadillos 4-40 ... + 27 Oe C, in the common vole + 37 ... + 32 ° C.
Rice. 2. The structure of the skin of a mammal(high magnification)
Fig.3. Curves of dependence of body temperature of various animals on the ambient temperature
Like other vertebrates, the skin of mammals consists of two layers: the outer one - the epidermis and the inner one - the cutis, or the skin itself. The epidermis, in turn, consists of two layers. The deep layer, represented by living cylindrical or cubic cells, is known as the malpighian or germ layer. Closer to the surface, the cells are flatter, inclusions of keratohyalin appear in them, which, gradually filling the cell cavity, leads to its horny degeneration and death. The superficially located cells finally become keratinized and gradually wear out in the form of small "dandruff" or whole flaps (as, for example, happens in seals). The wear of the stratum corneum of the epidermis is carried out by its constant increase due to cell division of the Malpighian layer.
The epidermis gives rise to many skin productions, the main of which are hair, claws, hooves, horns (except for deer), scales, and various glands. These formations are described below.
The skin itself, or cutis, is highly developed in mammals. It consists mainly of fibrous connective tissue, the plexus of fibers of which form a complex pattern. The lower part of the cutis consists of a very loose fibrous tissue in which fat is deposited. This layer is called the subcutaneous adipose tissue. It reaches its greatest development in aquatic animals - whales, seals, in which, due to the complete (in whales) or partial (in seals) reduction of the hairline and the physical characteristics of the aquatic environment, it performs a thermal insulation role. Some land animals also have large subcutaneous fat deposits. They are especially strongly developed in species that hibernate for the winter (ground squirrels, marmots, badgers, etc.). For them, fat during hibernation serves as the main energy material.
The thickness of the skin is significantly different in different species. As a rule, in species of cold countries with lush hair, it is thicker. Very thin and fragile skin is characteristic of hares, besides, it is poor in blood vessels. This has a certain adaptive meaning, expressed in a kind of autonomy. The predator, grabbing the hare by the skin, easily pulls a piece out of it, missing the animal itself. The resulting wound almost does not bleed and heals quickly. A peculiar cutaneous tail autonomy is observed in some mice, dormouse, jerboas. Their skin tail case easily breaks off and slides off the tail vertebrae, which makes it possible for the animal grabbed by the tail to escape from the enemy.
Hair is as characteristic of mammals as feathers are of birds or scales of reptiles. Only a few species have completely or partially lost their hair for the second time. So, dolphins have no hair at all, whales have only the makings of hair on their lips. In pinnipeds, the hairline is reduced, this is especially noticeable in walruses, to the least extent in eared seals (for example, in a seal), which are more connected with land than other types of pinnipeds.
The structure of the hair can be seen in the diagram in Figure 2. In it, one can distinguish between the trunk - the part protruding above the skin, and the root - the part sitting in the skin. The trunk consists of a core, a cortical layer and a skin. The core is a porous tissue, between the cells of which there is air; it is this part of the hair that gives it a low thermal conductivity. The cortical layer, on the contrary, is very dense and gives strength to the hair. The thin outer skin protects the hair from mechanical and chemical damage. The hair root in its upper part has a cylindrical shape and is a direct continuation of the trunk. In the lower part, the root expands with a direct continuation of the trunk. In the lower part, the root expands and ends with a flask-shaped swelling - a hair follicle, which, like a cap, covers the outgrowth of the cutis - the hair papilla. The blood vessels included in this papilla provide the vital activity of the cells of the hair follicle. The formation and growth of hair is due to the reproduction and modification of the cells of the bulb. The hair shaft is already a dead horn formation, unable to grow and change shape.
Immersed in the skin, the hair root sits in a hair bag, the walls of which consist of an outer layer, or hair bag, and an inner layer, or hair sheath. Ducts open into the funnel of the hair follicle sebaceous glands, the secret of which lubricates the hair and gives it greater strength and water resistance. Muscle fibers are attached to the lower part of the hair sac, the contractions of which cause the movement of the sac and the hair sitting in it. This movement causes the bristling of the beast.
Usually the hair sits in the skin not perpendicular to its surface, but more or less adjacent to it. This slope of the hair is not expressed equally in all species. It is least noticeable in underground animals, such as the mole.
The hairline is made up of different types of hair. The main ones are downy hair, or down, guard hairs, or spines, sensory hairs, or vibrissae. In most species, the basis of the coat is a dense low fluff, or undercoat. Longer, thicker and coarse guard hairs sit between the downy hairs. In underground animals, for example, the mole, the mole rat, the fur cover is almost always devoid of guard hairs. On the contrary, in adult deer, wild boars and seals, the undercoat is reduced and the coat consists mainly of an awn. Note that in young individuals of these animals, the undercoat is well developed.
The hairline changes periodically. Hair change, or molting, in some species happens twice a year: in spring and autumn: these are the squirrel, fox, arctic fox, mole. Other species molt only once a year; in the spring they lose their old fur, in the summer a new one develops, which finally matures only by autumn. Such, for example, gophers.
The density and height of the hairline in northern species vary significantly with the seasons. So, a squirrel has an average of 4,200 hairs per 1 cm2 on a rump in summer, 8,100 in winter, the same for a hare - 8,000 and 14,700. 4, in winter - 16.8 and 25.9; a hare hare has down in summer - 12.3, awn - 26.4, in winter 21.0 and 33.4. Tropical animals do not have such drastic changes due to the small difference in temperature conditions winter and summer.
Vibrissae are a special category of hair. These are very long, stiff hairs that perform a tactile function; they sit more often on the head (the so-called mustache), on the lower part of the neck, on the chest, and in some climbing tree forms (for example, on the squirrel) and on the belly. At the base of the hair follicle and in its walls there are nerve receptors that perceive the contact of the vibrissa rod with foreign objects.
Hair modifications are bristles and needles.
Other horny derivatives of the epidermis are represented by scales, nails, claws, hooves, hollow horns, and a horny beak. The scales of animals in their development and structure are quite similar to the formation of the same name in reptiles. Scales are most strongly developed in lizards and pangolins, in which it covers the entire body. A lot of mouse-like scales are on the legs. Finally, the presence of scales on the tail is characteristic of many marsupials, rodents, and insectivores.
The terminal phalanges of the fingers of the vast majority of animals bear horny appendages in the form of nails, claws or hooves. The presence of one or another of these formations and their structure are directly related to the conditions of existence and the way of life of animals (Fig. 4). So, in climbing animals, the fingers have sharp curved claws; in species that dig holes in the ground, the claws are usually somewhat simplified and expanded. Fast-running large mammals have hooves, while forest species (for example, deer), which often walk in swamps, have wider and flatter hooves. In the steppe (antelopes) and especially in mountain species (goats, rams), the hooves are small, narrow; their support area is much smaller than that of forest ungulates, which often walk on softened ground or on snow. Thus, the load per 1 cm2 of the sole of the Central Asian mountain goat is on average 850 g, for the elk - 500 g, for the reindeer - 140 g.
Rice. Fig. 4. Longitudinal section through the terminal phalanges of the fingers of an oblong (1), a predator ( II ), ungulate ( III ):
Horn formations are also the horns of bulls, antelopes, goats and rams. They develop from the epidermis and sit on bone rods, which are independent bones fused with the frontal bones. Deer antlers are of a different nature. They develop from the cutis and consist of bone substance.
The skin glands in mammals, unlike birds and reptiles, are very numerous and diverse in structure and function. The main types of glands are as follows: flow, sebaceous, odorous, milky.
The sweat glands are tubular, their deep parts look like a ball. They open directly from the surface of the skin or into the hair follicle. The secretion product of these glands is sweat, which consists mainly of water, in which urea and salts are dissolved. These products are not produced by the cells of the glands, but enter them from the blood vessels. The function of the sweat glands is to cool the body by evaporating the water they secrete on the surface of the skin and to excrete decay products. Therefore, these glands perform a thermoregulatory function. Most mammals have sweat glands, but not all of them are equally developed. So, they are very few in dogs and cats; many rodents have them only on the paws, in the groin and on the lips. Sweat glands are completely absent in cetaceans, lizards and some others.
In the development of the sweat glands, one can also notice the patterns of geographical and ecological plans. Thus, the average number of these glands per 1 cm2 in a zebu bred in the humid tropics is 1700, and in cattle bred in England (shorthorn) it is only 1060. The same feature can be traced when comparing species adapted to various degrees to arid conditions . As an indicator, we give the amount of evaporation, expressed in milligrams per minute per 100 cm2 of the skin surface. At a temperature of +37 0C for a donkey, this value was 17 mg / min, for a camel - only 3; at a temperature of +45 0С for a donkey - 35, for a camel - 15; finally, at a temperature of +50 0C for a donkey - 45, for a camel - 25 (Schmidt-Nielsen, 1972).
The secret of the skin glands, like other smelling secretions (for example, the genital and digestive tracts, urine, the secret of specialized glands), serve as the most important means of intraspecific communication - chemical signaling in mammals. The special significance of this type of signaling is determined by the range of its action and the duration of the signal. In animals that have certain habitats, individuals, pairs, families mark the area with odor marks that they leave on conspicuous objects: bumps, stones, stumps, individual trees, or simply on the surface of the earth.
The sebaceous glands have a nail-like structure and almost always open into the funnel of the hair bag. The fatty secret of these glands lubricates the hair and the surface layer of the epidermis of the skin, protecting them from wetting and wear.
The odorous glands represent a modification of the sweat or sebaceous glands, and sometimes a combination of both. Of these, we point to the anal glands of mustelids, the secret of which has a very pungent odor.
Smell marks are left by the parents on the young, in the nest, and on traces of movement outside the nest or the location of the young, if the nest is not being built. It is thanks to chemical signaling that deer, seals and such burrows as foxes, arctic foxes, sables, martens, voles, mice find their own, and not other people's cubs.
In general, odor signaling is of decisive importance for the development of mammalian behaviors.
The odorous glands of American skunks, or skunks (Mephitis), are especially highly developed, capable of spewing large portions of secretions over a considerable distance. Musk glands are found in musk deer, desman, beaver, muskrat; the significance of these glands is not entirely clear, but judging by the fact that they are most developed during the rut, their activity is apparently associated with reproduction; perhaps they stimulate sexual arousal.
The mammary glands are a kind of modification of simple tubular sweat glands. In the simplest case - in Australian monotremes - they retain a tubular structure and open into bags of hair located in groups on a small area of \u200b\u200bthe abdominal surface - the so-called glandular field. In the echidna, the glandular field is located in a special bag that develops during the breeding season and serves to bear the egg, and then the cub. In the platypus, the glandular field is located directly on the belly. Monotremes have no nipples, and the young lick the milk from their hair, where it comes from the hair follicles. In marsupials and placental mammary glands have a vine-like structure and their ducts open on the nipples. The location of the glands and nipples is different. Tree-climbing monkeys in hanging bats have only a pair of qockobs on their chests; in running ungulates, the nipples are located only in the inguinal region. In insectivorous and carnivorous nipples stretch in two rows along the entire lower surface of the body. The number of teats is directly related to the fecundity of the species and to some extent corresponds to the number of simultaneously born cubs. The minimum number of teats (2) is typical for monkeys, sheep, goats, elephants and some others; the maximum number of nipples (10 - 24) is characteristic of mouse-like rodents, insectivores, and some marsupials.
Muscular system mammals is very differentiated and is distinguished by a large number of diversely located muscles. Characteristic is the presence of a dome-shaped muscle - the diaphragm, which limits the abdominal cavity from the chest. Basically, its role is to change the volume of the chest cavity, which is associated with the act of breathing. Significant development is given to the subcutaneous, musculature, which sets in motion certain areas of the skin. In hedgehogs and pangolins, it causes the possibility of folding the body into a ball. The raising of quills in hedgehogs and porcupines, the "bristling" of animals, and the movement of sensory hairs - vibrissae - are also caused by the action of muscles. On the face, it is represented by mimic muscles, especially developed in primates.
Rice. 5 Rabbit Skeleton
Skeleton. (Fig. 5). Characteristic features in the structure of the spinal column of mammals are flat articular surfaces of the vertebrae (platycoel vertebrae), between which are cartilaginous discs (menisci), a clearly pronounced dissection of the spine into sections (cervical, thoracic, lumbar, sacral, caudal) and a constant number of sewing vertebrae. Deviations from these signs are rare and are secondary.
The cervical region is characterized by the presence of well-defined atlas and epistrophy - modified first two vertebrae, which is typical for amniotes in general. There are 7 cervical vertebrae. The only exceptions are the manatee, which has 6 cervical vertebrae, and sloth species, which have 6 to 10 vertebrae. Thus, unlike birds, in mammals the length of the neck is not determined by the number of cervical vertebrae. And their body length. The length of the cervical region varies greatly. It is most strongly developed in ungulates, for which the mobility of the head is very important in the extraction of food. The neck of predators is well developed. On the contrary, in burrowing rodents, and especially in excavations, the cervical region is short and their head mobility is low.
The thoracic region usually consists of 12-15 vertebrae; one of the armadillos and the beaked whale have 9, and the sloths of the genus Choloepus have 24. The ribs connected to the sternum (true ribs) are usually attached to the anterior thoracic vertebrae to seven. The remaining thoracic vertebrae bear ribs that do not reach the sternum (false ribs). The sternum is a segmented bone plate, ending with an elongated cartilage - the xiphoid process. The expanded anterior segment is called the manubrium of the sternum. In bats and in animals with well-developed forelimbs for digging, the sternum loses its clearly defined segmentation and bears a keel, which, like in birds, serves to attach the pectoral muscles.
In the lumbar region, the number of vertebrae varies from 2 to 9. These vertebrae bear rudimentary ribs.
The sacral section usually consists of four fused vertebrae. In this case, only the first two vertebrae are truly sacral, and the rest are tail vertebrae adhering to the sacrum. In fatty animals, the number of sacral vertebrae is three. And the platypus, like reptiles, has two. The number of caudal vertebrae is subject to the greatest variability. So, the gibbon has 3, and the long-tailed lizard has 49.
The general mobility of the spine in different species of animals is different. It is most strongly developed in small animals, which, when moving, often arch their backs in an arc. On the contrary, in large ungulates, all sections of the spine (except for the cervical and caudal) move slightly, and only the limbs work when they run.
Rice. 6. Scheme of the structure of the skull of mammals
The skull of mammals (Fig. 6) is characterized by a relatively larger braincase, which is associated with the large size of the brain. In young animals, the brain box, compared with the facial part, is usually relatively more developed than in adults. The number of individual bones in the skull of mammals is less than in lower groups of vertebrates. This is due to the fusion of a number of bones with each other, which is especially characteristic of the brain box. So, the main, lateral and upper occipital bones are fused; fusion of the ear bones leads to the formation of a single stony bone. The pterygosphenoid fuses with the main sphenoid bone, and the ocellar sphenoid fuses with the anterior sphenoid bone. There are cases of formation of more complex complexes, for example, the temporal and basal bones of a person. The sutures between bone complexes fuse relatively late, especially in the region of the braincase, which makes it possible to increase the volume of the brain as the animal grows.
The occipital region is formed by a single, as indicated, occipital bone, which has two condyles for articulation with the atlas. The roof of the skull is formed by paired parietal, frontal and nasal bones and an unpaired interparietal bone. The sides of the cranium are formed by squamous bones, from which the zygomatic processes extend outward and forward. The latter are connected to the zygomatic bone, which in turn is articulated in front with the zygomatic process of the maxillary bone. As a result, a zygomatic arch, which is very characteristic of mammals, is formed.
The bottom of the brain part of the skull is formed by the main and anterior cuneiform bones, and the bottom of the visceral part is formed by the pterygoid, palatine and maxillary bones. At the bottom of the skull, in the area of the auditory capsule, there is a tympanic bone characteristic only of mammals. The auditory capsules ossify, as already indicated, in several centers, but ultimately only one paired stony bone is formed.
The upper jaws consist of paired premaxillary and maxillary bones. The development of a secondary bone palate, formed by the palatine processes of the premaxillary and maxillary bones and the palatine bones, is characteristic. In connection with the formation of a secondary bony palate, the choanae do not open between the maxillary bones, as in other terrestrial vertebrates (except crocodiles and turtles), but behind the palatine bones. This structure of the palate prevents blockage of the choanae (i.e., a break in breathing) while the food bolus lingers in the oral cavity for chewing.
The lower jaw is represented only by paired dentaries, which are attached directly to the squamosal bones. The articular bone turns into an auditory bone - an anvil. Both of these bones, as well as the third auditory ossicle, the stirrup (homologous to the hyomandibular), lie in the cavity of the middle ear. The outer wall of the latter, as well as part of the external auditory meatus, is surrounded by the above-mentioned tympanic bone, apparently homologous to the angular bone - the lower jaw of other vertebrates. Thus, in mammals, a further transformation of a part of the visceral apparatus into the auditory apparatus of the middle and outer ear is observed.
The shoulder girdle of mammals is comparatively simple. Its basis is the scapula, to which the rudimentary coracoid grows. Only in monotremes does the coracoid exist as an independent bone. The clavicle is present in mammals whose forelimbs perform a variety of complex movements and in which the presence of the clavicle provides a stronger articulation of the humerus and strengthening of the entire shoulder girdle. Such, for example, are monkeys. Conversely, in species that move the forelimbs only or predominantly in a plane parallel to the main body axis, the clavicles are rudimentary or absent. Such are the ungulates.
The pelvic girdle consists of three paired bones typical of terrestrial vertebrates: the ilium, ischium, and pubis. In many species, these bones are fused into one innominate bone.
Fig.7. Hind limbs of digitigrade and plantigrade mammals.
The elements of the foot are blackened.
I - baboon monkey, II - dog, III - llama.
The skeleton of paired limbs retains all the main structural features of a typical five-fingered limb. However, due to the variety of conditions of existence and the nature of the use of the limbs, the details of their structure are very different (Fig. 7). In terrestrial forms, the proximal sections are significantly elongated. In aquatic animals, on the contrary, these sections are shortened, and the distal sections - the metacarpus, metatarsus, and especially the phalanges of the fingers - are greatly elongated. The limbs in this case are augmented into flippers, moving relative to the body mainly as a single unit. The movement of the departments of the limbs relative to each other is relatively poorly developed. In bats, only the first finger of the forelimbs is normally developed, the rest of the fingers are very much elongated; between them is a leathery membrane, which forms the main part of the wing surface. In fast-running animals, the tarsus, metatarsus, wrist and metacarpus are more or less vertical, and these animals rely only on the fingers. Such, for example, are dogs. In the most advanced runners - ungulates - the number of fingers is reduced. The first finger atrophies, and the animals either step on equally developed third and fourth fingers, between which the limb axis passes (artiodactyls), or one third finger, through which the limb axis passes (equids), is predominantly developed.
In this regard, we indicate the maximum speed of movement of some mammals (in km / h): short-tailed shrew - 4, red-backed vole - 7, wood mouse - 10, red squirrel - 15, wild rabbit - 32-40, hare - 55-72, red fox - 72, lion - 50, cheetah - 105-112, camel - 15-16, African elephant - 24-40, Grant's gazelle - 40-50.
The digestive organs are characterized by great complexity, which is expressed in the overall lengthening of the digestive tract, in its greater differentiation than in other vertebrates, and in the greater development of the digestive glands.
The digestive tract begins with the pre-oral cavity or vestibule of the mouth, located between the fleshy lips, cheeks and jaws characteristic only of mammals. In a number of species, the vestibule, expanding, forms large cheek pouches. This happens with hamsters, chipmunks, monkeys. Fleshy lips serve to seize food, and the vestibule of the mouth serves to temporarily reserve it. So, hamsters and chipmunks carry food supplies in their cheek pouches into their holes. There are no fleshy lips in monotremes and cetaceans.
Behind the jaws lies the oral cavity, in which food is subjected to mechanical grinding and chemical attack. Animals have four pairs of salivary glands, the secret of which contains the enzyme ptyalin, which converts starch into dextrin and maltose. The development of the salivary glands is in a certain dependence on the nature of nutrition. In cetaceans, they are practically not developed; in ruminants, on the contrary, they have received exceptionally strong development. So, a cow secretes about 56 liters of saliva per day, which is of great importance for wetting coarse food and for filling the stomach cavities with a liquid medium, where bacterial breakdown of food mass fiber occurs.
The secret of the buccal glands of bats, applied to the flying membranes, keeps them elastic and prevents them from drying out. The saliva of vampires that feed on blood has anticoagulant properties, i.e. protects blood from clotting. The saliva of some shrews is poisonous, the secretion of their submandibular gland causes death of the mouse in less than 1 min after injection. The toxicity of the salivary glands of primitive mammals is considered as a reflection of their phylogenetic relationship with reptiles.
Mammals are heterodont, i.e. their teeth are differentiated into incisors, canines, premolars, or false molars, and molars. The number of teeth, their shape and function differ significantly in different groups of animals. Thus, for example, little specialized insectivores have a large number of relatively weakly differentiated teeth. Rodents and lagomorphs are characterized by a strong development of one pair of incisors, the absence of fangs and a flat chewing surface of the molars. This structure of the dental system is associated with the nature of nutrition: they gnaw or gnaw vegetation with incisors, and grind food with molars, like millstones. Carnivores are characterized by strongly developed fangs, which serve to grasp, and often to kill prey. The molars of carnivores have cutting tops and flat chewing protrusions. The posterior false-root tooth of the upper jaw and the first true-root tooth of the lower jaw in carnivores are usually distinguished by their size; they are called carnivorous teeth.
The total number of teeth and their distribution into groups for species of animals is quite definite and constant and serves as an important systematic feature.
The teeth sit in the cells of the jaw bones, i.e. they are thecodont, and in most animal species they change once in a lifetime (the dentition is diphyodont).
A muscular tongue is placed between the branches of the lower jaw, which serves partly for grasping food (bovine, anteaters, lizards) and for lapping water, partly for turning food over in the mouth during chewing.
Behind the oral region is the pharynx, into the upper part of which the internal nostrils and Eustachian tubes open. On the lower surface of the pharynx is a gap leading to the larynx.
The esophagus is well defined. Its musculature is often smooth, but in some, for example, in ruminants, striated muscles penetrate here from the pharyngeal region. This feature provides an arbitrary contraction of the esophagus when belching food.
The stomach is distinctly isolated from other sections of the digestive tract and is supplied with numerous glands. The volume of the stomach and internal structure different in different species, which is associated with the nature of the food. The stomach is most simply arranged in monotremes, in which it looks like a simple bag. Most of the stomach is divided into more or less sections.
The complication of the stomach is associated with the specialization of nutrition, for example, the absorption of a huge mass of roughage (ruminants), or the underdevelopment of oral chewing of food (some species that feed on insects). In some South American anteaters, in the outlet part of the stomach, a section is differentiated with folds so hard that they function as teeth that grind food.
The stomach of ruminant ungulates, such as a cow, is very complex. It consists of four sections: 1) a scar, the inner surface of which bears hard swellings; 2) mesh, the walls of which are divided into cells; 3) books with walls bearing longitudinal folds; 4) abomasum, or glandular stomach. Feed masses that have fallen into the rumen undergo fermentation under the influence of saliva and bacterial activity. From the scar, food, thanks to peristaltic movements, enters the mesh, from where, by belching, it enters the mouth again. Here the food is crushed with teeth and abundantly moistened with saliva. The semi-liquid mass thus obtained is swallowed and, through a narrow groove connecting the esophagus with the book, enters this latter and then the abomasum.
The described adaptation is of great importance, since the food of ruminants is an indigestible plant mass, and a huge number of fermentative bacteria live in their stomach, the activity of which significantly contributes to the digestion of food.
The intestine itself is divided into thin, thick and straight sections. In species that feed on coarse plant food (for example, in rodents), a long and wide cecum leaves on the border of the thin and thick sections, ending in some animals (for example, hares, semi-monkeys) with a worm-like process. The caecum plays the role of a "fermentation tank" and is developed the stronger, the more vegetable fiber the animal absorbs. In mice that feed on seeds and partly on vegetative parts of plants, the caecum is 7-10% of the total length of all sections of the intestine, and in voles that feed mostly on vegetative parts of plants, it is 18-27%. In carnivorous species, the caecum is poorly developed or absent.
In the same connection, the length of the large intestine also varies. In rodents, it is 29-53% of the total length of the intestinal tract, in insectivores and bats - 26-30%, in predators - 13-22. The total length of the intestine varies greatly. In general, herbivorous species have relatively longer intestines than omnivores and carnivores. So, in some bats, the intestines are 2.5 times longer than the body, in insectivores - 2.5 - 4.2, in predators - 2.5 (weasel), 6.3 (dog), in rodents - in 5.0 (midday gerbil), 11.5 (guinea pig), horse - 12.0, sheep - 29 times.
Describing the structure and functioning of the digestive tract, let us briefly touch on the problem of providing the body of mammals with water.
Many species of predators and ungulates regularly visit the watering place. Others are content with water obtained from succulent food. However, there are those who never drink and feed on very dry food, such as many desert rodents. In this case, the main source of water supply is the water that occurs during metabolism, the so-called metabolic water.
Metabolic water is one of the essential products of the metabolism of all organic substances in the body. However, the metabolism of different substances produces different amounts of water. The first place is occupied by fats. When using 1 kg of fat per day, about 1 l of water is formed, 1 kg of starch - 0.5 l, 1 kg of proteins - 0.4 l (Schmidt-Nielsen).
The liver is located under the diaphragm. The yellow duct flows into the first loop of the small intestines. The duct and pancreas, which is located in the fold of the peritoneum, flows into the same section of the intestine.
Respiratory system. As with birds, the lungs are essentially the only respiratory organ in mammals. The role of the skin in gas exchange is insignificant: only about 1% of oxygen enters through the skin blood vessels. This is understandable if we take into account, firstly, the keratinization of the epidermis and, secondly, the negligible total surface of the skin compared to the total respiratory surface of the lungs, which is 50-100 times larger than the surface of the skin.
The complication of the upper larynx is characteristic (Fig. 8). At its base lies the annular cricoid cartilage; the anterior and lateral walls of the larynx are formed by the thyroid cartilage characteristic only of mammals. Above the cricoid cartilage on the sides of the dorsal side of the larynx are paired arytenoid cartilages. A thin petaloid epiglottis adjoins the anterior edge of the thyroid cartilage. Between the cricoid and thyroid cartilages are small saccular cavities - the ventricles of the larynx. The vocal cords in the form of paired folds of the mucous membrane of the larynx lie between the thyroid and arytenoid cartilages. The trachea and bronchi are well developed. In the region of the lungs, the bronchi are divided into a large number of small branches. The smallest branches - bronchioles - end in vesicles - alveoli, which have a cellular structure (Fig. 9). This is where the blood vessels branch. The number of alveoli is huge: in predators there are 300-500 million, in sedentary sloths - about 6 million. In connection with the appearance of alveoli, a huge surface is formed for gas exchange. So, for example, the total surface of the alveoli in humans is 90 m2. When calculated per unit of respiratory surface (in cm2), there are 6 alveoli in a sloth, 28 in a domestic cat, 54 in a house mouse, and 100 in a bat.
Fig.8. rabbit larynx
The exchange of air in the lungs is due to a change in the volume of the chest, resulting from the movement of the ribs and a special, dome-like muscle protruding into the chest cavity - the diaphragm. The number of respiratory movements depends on the size of the animal, which is associated with a difference in the intensity of metabolism.
Ventilation of the lungs not only causes gas exchange, but is also essential for thermoregulation. This is especially true for species with underdeveloped sweat glands. In them, the cooling of the body when it is overheated is largely achieved by increasing the evaporation of water, the vapors of which are excreted along with the air exhaled from the lungs (the so-called polyp).
Fig.9. Scheme of the structure of the pulmonary vesicles of a mammal
Table 1. Oxygen consumption by mammals of different sizes
Table 2. Respiratory rate per minute in mammals depending on
medium temperature
Table 3. Polyp value for heat loss in the dog
Circulatory system(Fig. 10). As in birds, there is only one, but not the right, but the left aortic arch, extending from the thick-walled left ventricle. The main arterial vessels depart from the aorta differently. Usually, a short innominate artery departs from the aorta, which is divided into the right and subclavian arteries, the right and left carotid arteries, while the left subclavian artery departs independently from the aortic arch. In other cases, the left carotid artery does not depart from the innominate artery, but independently from the aortic arch. The dorsal aorta, like in all vertebrates, lies under the spinal column and gives off a number of branches to the muscles and internal organs.
The venous system is characterized by the absence of portal circulation in the kidneys. The left anterior vena cava only in a few species flows into the heart on its own; more often it merges with the right anterior vena cava, which pours all the blood from the anterior part of the body into the right atrium. Very characteristic is the presence of remnants of the cardial veins - the so-called unpaired veins. In most species, such a right unpaired vein independently flows into the anterior vena cava, and the left unpaired vein loses its connection with the vena cava and flows through the transverse vein into the right unpaired vein (Fig. 10).
The relative sizes of the heart are different in species with different lifestyles and, ultimately, with different metabolic rates.
Fig.10. Scheme of the structure of the circulatory system of mammals
The total amount of blood in mammals is greater than in lower vertebrate groups. The blood of mammals also favorably differs in a number of its biochemical properties, partly related to the non-nuclear nature of erythrocytes.
Mammals have not only a relatively large amount of blood, but, most importantly, a greater oxygen capacity. In turn, this is due to a large number of red blood cells and a large amount of hemoglobin.
Peculiar adaptations arise during an aquatic lifestyle, when the possibility of atmospheric respiration is periodically interrupted. This is expressed, on the one hand, in a sharp increase in the amount of oxygen-binding globin in the muscles (myoglobin) - about 50 50 of the total globin of the body. In addition, in animals immersed in water for a long time, the peripheral blood circulation is turned off and the blood circulation of the brain and heart remains at the same level.
Nervous system. The brain (Fig. 11) is characterized by relatively very large sizes, which is caused by an increase in the volume of the hemispheres forebrain and cerebellum.
The development of the forebrain is expressed mainly in the growth of its roof - the cerebral fornix, and not in the striatum, as in birds. The roof of the forebrain is formed by the growth of the nervous substance of the walls of the lateral ventricles. The resulting fornix is called the secondary fornix or neopallium; it is made up of nerve cells and non-fleshy nerve fibers. In connection with the development of the cerebral cortex, the gray medulla in mammals is located on top of the white matter. The centers of higher nervous activity are located in the cerebral cortex. The complex behavior of mammals, their complex reactions to various external stimuli, are directly related to the progressive development of the cortex of the forebrain. The cortex of both hemispheres is connected by a commissure of white nerve fibers, the so-called corpus callosum.
The ratio of the mass of the forebrain hemispheres to the mass of the entire brain is different in mammals of different taxonomic groups. In hedgehogs, it is 48, in squirrels - 53, in wolves - 70, in dolphins - 75%.
The cortex of the forebrain in most species is not smooth, but covered with numerous furrows that increase the area of the cortex. In the simplest case, there is one Sylvian sulcus that separates the frontal lobe of the cortex from the temporal lobe. Further, a transversely running Roland furrow appears, separating the frontal lobe from the occipital lobe from above. The higher representatives of the class have a large number of furrows. The diencephalon is not visible from above. The epiphysis and pituitary are small.
The midbrain is characterized by its division by two mutually perpendicular grooves into four hillocks. The cerebellum is large and differentiated into several sections, which is associated with a very complex nature of movements in animals.
Sense organs. The olfactory organs are highly developed in mammals and play a huge role in their life. With the help of these organs, mammals identify enemies, look for food, and also each other. Many species sense smells several hundred meters away and are able to detect food objects that are underground. Only in fully aquatic animals (whales) is the sense of smell reduced. Seals have a very keen sense of smell.
The progressive development of the described organs is expressed mainly in an increase in the volume of the olfactory capsule and in its complication through the formation of a system of olfactory shells. Some groups of animals (marsupials, rodents, ungulates) have a separate section of the olfactory capsule that opens independently into the palatonasal canal, the so-called Jacobson organ, which has already been described in the chapter on reptiles.
The organ of hearing in the overwhelming majority of cases is very strongly developed. In addition to the inner and middle ear, which are also available in lower classes, it includes two more new departments: the external auditory meatus and the auricle. The latter is absent only in water and underground animals (whales, most pinnipeds, mole rats and some others). The auricle significantly enhances the subtlety of hearing. It is especially strongly developed in nocturnal animals (bats) and in forest ungulates, desert dogs and some others.
The inner end of the ear canal is covered by the tympanic membrane, behind which lies the middle ear cavity. In the latter, mammals have not one auditory ossicle, as in amphibians, reptiles and birds, but three. The malleus (homologue of the articular bone) rests against the barbarous membrane, an anvil (homologue of the quadrate bone) is movably attached to it, which in turn is articulated with the stirrup (homologue of the hyomandidular), and this latter rests against the oval window of the membranous labyrinth of the inner ear. The described system provides a much more perfect transmission of the sound wave captured by the auricle and passed through the ear canal to the inner ear. In the structure of the latter, attention is drawn to the strong development of the cochlea and the presence of the organ of Corti - the finest fibers, which, among several thousand, are stretched in the cochlear canal. When perceiving sound, these fibers resonate, which ensures a more subtle hearing of animals.
A number of animals have been found to be capable of sound location (echolocation).
The organs of vision in the life of mammals are much less important than in birds. But they usually do not pay attention to motionless objects, and even such cautious animals as foxes, hares, and moose can come close to a standing person. The visual acuity and development of the eyes, of course, are different and are related to the conditions of existence. Night animals and animals of open landscapes (for example, antelopes) have especially large eyes. In forest animals, the eyesight is less acute, while in the underground animals, the eyes are reduced and sometimes covered with a leathery membrane (mole rat, blind mole).
Accommodation in mammals occurs only by changing the shape of the lens under the action of the ciliary muscle. At small rodents(voles, mice) there is practically no ability to accommodate, which is associated with predominantly nocturnal activity and insignificance of visibility.
Color vision in mammals is poorly developed compared to birds. Only the higher apes of the eastern hemisphere can distinguish almost the entire spectrum. The European bank vole can only distinguish between red and yellow. In the opossum, the forest polecat, and a number of other species, color vision has not been found at all.
A characteristic feature of the tactile organs of mammals is the presence of tactile hairs, or vibrissae.
excretory system. The kidneys in mammals are pelvic. Trunk kidneys in mammals are an embryonic organ and are subsequently reduced. Mammalian metanephric kidneys are compact, usually bean-shaped organs. Their surface is often smooth, sometimes tuberculate (ruminants, cats), and only in some (for example, in cetaceans) the kidneys are divided by intercepts into lobes.
The main end product of protein metabolism in mammals (as well as in fish and amphibians), unlike reptiles and birds, is not uric acid, but urea.
This type of protein metabolism in mammals undoubtedly arose in connection with the presence of the placenta, through which the developing embryo can receive unlimited water from the mother's blood. On the other hand, through the placenta (more precisely, the system of its blood vessels), toxic products of protein metabolism can also be excreted indefinitely from the developing embryo.
In the medulla there are direct collecting tubules, which concentrate into a group and open at the end of the papillae protruding into the renal pelvis. From the renal pelvis, the ureter departs, which in the vast majority of species flows into the bladder. In monotremes, the ureter empties into the urogenital sinus, from which it enters the bladder. Urine is excreted from the bladder through an independent urethra.
The excretory system is partially performed by the sweat glands, through which solutions of salts and urea are excreted. This way displays no more than 3% of the nitrogenous products of protein metabolism.
Reproduction organs (Fig. 11). The sex glands of the male - the testes - have a characteristic oval shape. In monotremes, some insectivorous and edentulous, in elephants and cetaceans, they are in the body cavity throughout their lives. In most other animals, the testicles are initially located in the body cavity, but as they mature, they descend and fall into a special sac located outside - the scrotum, which communicates with the body cavity through the inguinal canal. Adjacent to the testis is a granular body elongated along its axis - an appendage of the testis, morphologically representing a tangle of highly convoluted vas deferens and homologous to the anterior part of the trunk kidney. A paired vas deferens, homologous to the Wolffian canal, departs from the appendage, which flows into the urogenital canal at the root of the penis, forming paired compact bodies with a ribbed surface - the seminal vesicles. In mammals, they represent the gland, the secret of which takes part in the formation of the liquid part of the sperm; in addition, it has a sticky consistency and, due to this, apparently serves to prevent the flow of sperm from the female genital tract.
At the base of the penis lies the second paired gland - the prostate, the ducts of which also flow into the initial part of the urogenital canal. The secret of the prostate gland is the main part of the fluid in which the spermatozoa secreted by the testes float. Ultimately, semen, or ejaculate, is a combination of fluid secreted by the prostate and seminal vesicles (and some other glands) and the sperm themselves.
On the lower side of the copulatory member is the already mentioned urogenital canal. Above and on the sides of this channel lie the cavernous bodies, the internal cavities of which are filled with blood during sexual arousal, as a result of which the penis becomes elastic and increases in size. In many mammals, the strength of the penis is also determined by a special long bone located between the cavernous bodies. These are carnivores, pinnipeds, many rodents, some bats, etc.
Fig.11. Urogenital organs of a rat ( I - male, II - females)
Paired ovaries always lie in the body cavity and are attached to the dorsal side of the abdominal cavity by mesentery. The paired oviducts, homologous to the Müllerian canals, open with their anterior ends into the body cavity in the immediate vicinity of the ovaries. Here the oviducts form wide funnels. The upper convoluted section of the oviducts represents the fallopian tubes. Next come the expanded sections - the uterus, which open into an unpaired section in most animals - the vagina. The latter passes into a short urogenital canal, into which, in addition to the vagina, the urethra opens. On the ventral side of the urogenital canal there is a small outgrowth - the clitoris, which has cavernous bodies and corresponds to the penis of the male. Curiously, some species have a bone in the clitoris.
The structure of the female reproductive tract varies significantly in different groups of mammals. So, in monotremes, the oviducts are paired throughout and are differentiated only into the fallopian tubes and uterus, which open with independent openings into the urogenital sinus. In marsupials, the vagina is isolated, but often it remains paired. In placental vaginas, the vagina is always unpaired, and the upper sections of the oviducts, to one degree or another, retain a paired character. in the simplest case, the uterus is a steam room and its left and right sections open into the vagina with independent openings. Such a uterus is called double; it is characteristic of many rodents, some edentulous. The uterus can only be connected in the lower section - a bifid uterus of some rodents, bats, predators. The fusion of a significant part of the left and right uterus leads to the formation of a bicornuate uterus of carnivores, cetaceans, and ungulates. Finally, in primates, semi-monkeys, and some bats, the uterus is unpaired - simple, and only the upper sections of the oviducts - the fallopian tubes - remain paired.
Placenta. During the development of the embryo in the uterus of mammals, an extremely characteristic formation for them is formed, known as the placenta or placenta (Fig. 12). Only in single passers there is no placenta. The marsupials have the rudiments of the platy. The placenta arises by the fusion of the outer wall of the allantois with the serosa, resulting in the formation of a spongy formation - the chorion. The chorion forms outgrowths - villi that connect or grow together with a loosened area of \u200b\u200bthe epithelium of the uterus. In these places, the blood vessels of the child and maternal organisms intertwine (but do not merge), and thus a connection is established between the blood channels of the embryo and the female. As a result, gas exchange is ensured in the body of the embryo, its nutrition and removal of decay products.
Fig.12. Rabbit fetus at the end of the twelfth day
The placenta is already characteristic of marsupials, although they are still primitive; villi are not formed in the chorion, and there is, like in ovoviviparous lower vertebrates, a connection between the blood vessels of the uterus and the yolk sac (the so-called "yolk placenta"). In higher placental animals, the chorion always forms outgrowths - villi that connect to the walls of the uterus. The nature of the location of the villi is different in different groups of animals. Based on this, three types of placenta are distinguished: diffuse, when the villi are distributed evenly over the chorion (cetaceans, many ungulates, semi-monkeys); lobed, when the villi are collected in groups, distributed over the entire surface of the chorion (most ruminants); discoidal, - the villi are located on a limited, disc-shaped section of the chorion (insectivores, rodents, monkeys).
Origin and evolution of mammals
The ancestors of mammals were primitive Paleozoic reptiles, which had not yet had time to acquire a narrow specialization, so characteristic of most subsequent groups of reptiles. Such are the Permian animal-toothed from the subclass of animal-like. Their teeth were in the alveoli. Many had a secondary bony palate. The quadrate bone and articular bone are reduced; the dentary, on the contrary, was very strongly developed, and so on.
The progressive evolution of mammals has been associated with the acquisition of such decisive adaptations as heat body, the ability to thermoregulate, live birth and mainly highly developed nervous activity, which provided complex behavior animals and their various adaptive reactions to the impact of the environment. Morphologically, this is expressed in the division of the heart into four chambers while maintaining one (left) aortic arch, which causes the immiscibility of arterial and venous blood, in the appearance of a secondary bone palate that provides breathing during meals, in the complication of the skin, which plays an important role in thermoregulation, in the appearance of a secondary cerebral fornix, etc.
The separation of mammals from animal-toothed reptiles should be attributed to the beginning of the Triassic or even to the end of the Permian (ie, the end of the Paleozoic era). There is very fragmentary and often not very reliable information about the early groups. In most cases, material on early Mesozoic mammals is limited to individual teeth, jaws, or small fragments of skulls. In the deposits of the Upper Triassic, owl-like multitubercles were found, which received their name in connection with the presence of numerous tubercles on the molars. This was a specialized group of animals with very strongly developed incisors without fangs. They were small, with a rat, the largest reached the size of a marmot. The multituberculates were specialized herbivorous animals, and their purpose cannot be considered the ancestors of subsequent groups of mammals. One can only assume that their early forms gave rise to monotremes (their teeth are very similar to the teeth of the platypus embryo), but there is no direct evidence for this, since single-tremes are reliably known only from deposits of the Quaternary period (Pleistocene).
Forms closer to the alleged ancestors of modern mammals appeared on Earth in the middle of the Jurassic period. These are the so-called three-tubercles. Their teeth are less specialized than those of the multituberous ones, the dentition is continuous. The trituberculates were small animals, obviously feeding mainly on insects, maybe other small animals and reptile eggs. Biologically, they were to a certain extent close to terrestrial and arboreal insectivores. Their brain was small, but still much larger than that of the animal-toothed reptiles. The main group of trituberculates - pantotheria - was the source for marsupials and placentals. Unfortunately, there is no, even indirect, data on their reproduction.
Marsupials appear in the Cretaceous period. Their earliest finds are confined to the Lower Cretaceous deposits of North America and the Lower Tertiary deposits of North America and Eurasia. Thus, the northern hemisphere, where they were widespread at the beginning of the Tertiary period, should be considered the homeland of marsupials. Even before the end of this time, they were supplanted here by more highly organized placentals and are now preserved only in Australia, New Guinea, Tasmania, South America and partly in North America (1 species) and on the island of Sulawesi (1 species).
The most ancient group of marsupials is the family of opossums, the remains of which were found in the Early Cretaceous deposits of North America. Now distributed in South, Central America and in the southern regions of North America.
In South America, marsupials were relatively numerous until the middle of the Tertiary period, when there were no placental ungulates and carnivores. After the Miocene, marsupials here were almost completely replaced by placental ones, and only a few specialized species have survived.
Placental mammals also arose in the Cretaceous period, at least not later than the marsupials from the above-mentioned trituberculates and represent an independent, to a certain extent parallel to the marsupials, branch of animals. As studies by V.O. Kovalevsky, in the Cretaceous they already evolved in very different directions. The most ancient group of placentals is the order of insectivores. These primitive animals are found in the Upper Cretaceous of Mongolia. They were partly terrestrial, partly arboreal, and gave rise to most of the major groups of subsequent planetary ones. Arboreal insectivores, adapted to flight, gave rise to bats. The branch, adapted to predation, gave rise at the beginning of the Tertiary period to the ancient primitive predators - creodonts. They were widespread only for a short time. Already at the end of the Oligocene, when the sluggish ungulates of the early Tertiary period were replaced by more mobile ones, creodonts were forced out by their descendants - more specialized predators. At the end of the Eocene - the beginning of the Oligocene, a branch of aquatic animals - pinnipeds - separated from predators. In the Oligocene, ancestral groups of a number of modern families of carnivores (viverras, martens, dogs, cats) already existed.
Ancient ungulates, or condylartras, are also descended from creodonts - small animals, no larger than a dog. They originated in the Paleocene and were omnivores. The limbs were five-fingered with a slightly reinforced third finger and shortened first and fifth fingers. Condylartra did not last long, and already at the beginning of the Eocene two independent branches arose from them: orders of artiodactyls and equids. Proboscis appear in the Eocene. In general, the group of ungulates has a combined character. separate orders of ungulates descended from their closest descendants - creodonts.
The external similarity between individual orders is the result of adaptation to similar living conditions. Some units became extinct in the Tertiary time. Such, for example, is a very peculiar group of ungulates that developed in South America during the period of isolation from other continents and gave rise to a number of parallel branches with other ungulates. There were animals like horses, rhinos, hippos.
A number of other orders arose directly from the insectivores at the very beginning of the Tertiary period. Such, for example, are edentulous, rodents, primates.
Fossil monkeys have been known since the Paleocene. Tree monkeys of the Lower Oligocene - propliopithecus - gave rise to gibbons and large, close to anthropoid ramapitecus from the Miocene of India. Of great interest are the australopithecuses found in the Quaternary deposits of South Africa, and especially the higher apes plesianthropus and paranthropus.
To date, the view that the class of mammals has a polyphyletic origin is gaining more and more recognition, i.e. its individual branches arose from different groups of animal-like reptiles. This is most correct for monotremes, which probably originated from a group close to multituberculous.
Along with this, there is no doubt that the marsupials and placentals, together with the extinct panthotheres, are a natural group united by a common origin. In this regard, some believe that only these three groups should be classified as a class, and the single-pass ones should be separated into an independent class.
Even if we do not follow this extreme view, we still have to admit that the difference between the usually accepted three subclasses - oviparous, marsupial and placental - is not the same in terms of anatomical-physiological and phylogenetic. Based on this, a different class system of mammals is now often adopted, in which the isolation of egg-laying animals is emphasized.
Ecology of mammals
Conditions of existence and general distribution. Direct proof of the biological progress of mammals is the breadth of their geographical and biotopic distribution. Mammals are found almost everywhere on the globe, with the exception of Antarctica. Seals have been observed on the coast of this desert land. A number of species of land animals are observed on the islands of the Arctic Ocean. Even on such a piece of land as remote from the mainland and lost in the Arctic Ocean as Solitude Island (Kara Sea), arctic foxes and reindeer have been repeatedly observed. Mammals inhabit the expanses of all oceans, reaching, as observations during the drift of the Soviet stations "North Pole" and the icebreaker "Georgy Sedov", reach the spaces adjacent to North Pole. These are pinnipeds and cetaceans (narwhals).
The limits of the vertical distribution of animals are also great. So, in the Central Tien Shan at an altitude of 3-4 thousand meters, there are numerous voles, marmots, wild goats, sheep, a snow leopard, or an irbis, is common. In the Himalayas, rams spread up to 6 thousand meters, and single visits of wolves were observed here even at an altitude of 7150 m.
Even more indicative is the prevalence of the class of mammals in various living environments. Only in this class, along with terrestrial animals, are there forms that actively fly through the air, real aquatic inhabitants that never go to land, and, finally, inhabitants of the soil, whose entire life passes in its thickness. Undoubtedly, the class of animals as a whole is characterized by a wider and more perfect adaptability than other vertebrates to various living conditions.
If we consider individual species, then one can easily find a large number of cases when their distribution is associated with narrowly limited conditions of existence. Only under conditions of relatively high and even temperatures can many apes, primarily anthropoids, as well as hippos, rhinos, tapirs and a number of others, successfully exist.
The direct effect of humidity on the distribution of mammals, as well as on the distribution of birds, is small. Only a few species with bare or almost hairless skin suffer from dryness. These are hippos and buffaloes, common only in humid tropical areas.
Many mammals are very demanding on soil and orographic conditions. So, some types of jerboas live only in loose sands; similar conditions are necessary for the fine-toed ground squirrel. On the contrary, a large jerboa lives only on dense soils. Soil-dwelling moles and mole rats avoid areas of hard ground that are difficult to tunnel through. Sheep inhabit only areas with a varied topography, where there are extensive pastures and a wide horizon. Goats are even more demanding on the conditions of the relief, they are distributed mainly in the conditions of a rocky landscape. For wild boars, places with soft, moist soil are favorable, in which they find food. On the contrary, horses, antelopes, camels definitely avoid viscous ground, for movement on which their limbs are not adapted.
In general, the distribution of mammals (as well as animals of any other group) is closely related to environmental conditions. Instead, it is important to emphasize that this relationship is more complex than in the lower terrestrial vertebrates. Mammals are relatively less dependent on the direct influence of climatic factors. Their adaptations are to a greater extent connected with the peculiarities of behavior, which depend on highly developed higher nervous activity.
No class of vertebrates has produced such a variety of forms as mammals. The reason for this lies in the long (since the Triassic) progressive evolution of the class, during which some of its branches settled around the globe and adapted to extremely diverse conditions of existence.
Initially, mammals were, apparently, terrestrial and, perhaps, terrestrial-arboreal animals, the adaptive evolution of which led to the emergence of the following main ecological types of animals:
Ground
Underground
Flying.
Each of these groups is divided into smaller branches, different from the degree and nature of connection with a particular environment.
I . land animals- the most extensive group of mammals that inhabited almost the entire land of the globe. Its diversity is caused directly by the wide distribution that has brought members of this group to face very different conditions of existence. Within the group being broken down, two main branches can be distinguished: forest animals and animals of open habitats.
1. Animals inhabiting the forest and thickets of large shrubs exhibit varying degrees and different forms connection with the living conditions created in forest and shrub plantations. The general conditions faced by the species of the group under consideration are the following: the closedness of the lands and, in this regard, the ability to see animals only up close, the presence a large number shelters, layered habitat, diversity of food.
The most specialized group is wood-climbing animals. They spend most of their lives in trees, getting food there, arranging nests for reproduction and rest; on the trees they are saved from enemies. Representatives of this group are among different orders of animals: from rodents - squirrels, flying squirrels; from predatory - some bears (South Asian), some martens; from edentulous - sloths, some anteaters; moreover, lemurs, many monkeys, etc.
Adaptations for life on trees are diverse. Many climb tree bark and boughs using sharp claws. These are squirrels, bears, martens, anteaters. Lemurs and monkeys have grasping paws with highly developed fingers, with which they grab onto branches or bumps in the bark. Many South American monkeys, as well as tree anteaters, tree porcupines, and of the marsupials, the possum has a tenacious tail.
Many animals are capable of jumping far from branch to branch, sometimes after swinging; such are gibbons and spider monkeys. More often, the jump is accompanied by more or less pronounced planning. The ability to plan is best expressed in flying squirrels (flying squirrels) and the winged wing, which have leathery membranes on the sides of the body. In squirrels and martens, the rudiments of planning ability are associated with a long fluffy tail: this is easy to see when directly observing these animals. In addition, this is confirmed by the greater development of the tail in these species compared to semi-arboreal species close to them.
The food of animals of this group is predominantly vegetable. Among them there are species that are quite specialized, for example, a squirrel that feeds mainly on coniferous seeds. Some monkeys feed mainly on fruits. Tree bears feed on a more varied diet: fleshy fruits, berries, vegetative parts of plants. Predatory species of animals of this group also eat vegetable food (seeds, berries), but, in addition, they catch birds and animals, which are hunted not only in trees, but also on the ground.
These animals arrange nests for hatching and resting on trees from branches or in hollows, for example, squirrels, flying squirrels.
Among the forest animals there are many species leading a semi-arboreal, semi-terrestrial way of life. They only partially forage in trees, and nests are arranged in various settings.
Among rodents, the chipmunk belongs to this group. He spends most of his time on the ground, where he feeds on berries, seeds of cereals and legumes, and mushrooms. It climbs trees very well, but it cannot even jump from branch to branch as far as a squirrel - its tail is shorter and less densely pubescent. Nests more often in burrows under tree roots or in hollows of fallen trees.
All listed species are strictly forest. However, they do not always resort to trees as a place for obtaining food and building a nest and spend a lot of time on the ground.
Finally, there are many species that also live only or mainly in the forest, but lead a terrestrial lifestyle. These are brown bears, wolverines, column ferrets, elk, real deer, roe deer. They get all their food from the ground. They do not climb trees (with rare exceptions) and the cubs are brought out in burrows (columns, wolverine) or on the surface of the earth (deer, elk, roe deer). For these species, the value of trees is mainly to provide shelter; only partly trees (more precisely, their branches and bark) serve them as food.
Thus, using the example of the three above groups of forest animals, one can trace the different nature of the relationship between forest animals and woody vegetation.
2. The inhabitants of open spaces are no less numerous and diverse group. Characteristics the conditions of their existence are as follows: weakly expressed tiered habitats, their “openness” and the absence or small number of natural shelters, which makes peaceful animals visible from afar as predators, and, finally, an abundance of plant food, mainly in the form of herbaceous plants. Representatives of this ecological group of animals are among different orders: marsupials, insectivores, rodents, carnivores, ungulates, but it is based on herbivorous animals - rodents and ungulates.
In this living environment, three main types of animals have developed:
A) Ungulates - large herbivorous species, consumers of roughage in the form of grass, sometimes hard and dry. They spend a lot of time grazing and move widely. Their ability for long and fast movement is also associated with the search for water rare in the steppes and deserts and with the need to flee from enemies.
These animals (unlike most other mammals) do not build any dwellings or temporary shelters. Adaptive features, in addition to fast running, are also relatively large visual acuity, large sizes of animals and a head held high on a long neck. Many species can go without water for a long time, being content with the moisture received from the grass. The birth of well-developed cubs, which already on the first day of existence can run after their mother, is of great importance.
In addition to ungulates (horses, antelopes, camels, giraffes), large species of terrestrial kangaroos undoubtedly belong to the same ecological group. Like ungulates, they inhabit open, steppe-desert spaces, feed on grass, graze a lot, see well and flee from enemies by running.
B) a group of jerboas - small animals, inhabitants of desert spaces with sparse vegetation and a poor animal population. To get food, they have to move a lot and quickly (up to 20 km/h). The ability to move quickly is not achieved by running on four legs, as in ungulates, but by a more or less developed ability to jump on very long hind legs (the so-called "ricocheting"). A similar feature is characteristic of mammals of open spaces that are completely systematically different. In addition to jerboas, it is characteristic of gerbils, North American kangaroo rats, African striders, African jumping insectivores, and some small Australian marsupials.
Unlike the previous group, the species under consideration feed not only on grass, but also on succulent bulbs or tubers of plants, and some on insects. They never drink and are content with water obtained from food.
The second essential feature of the described group is the presence in its species of permanent or temporary shelters in the form of holes. They dig very quickly, and many species build a new (albeit simply arranged) burrow daily. Due to the presence of holes, i.e. safe havens in which childbirth occurs, their pregnancy is short and the cubs are born helpless.
C) a group of gophers - small and medium-sized rodents that inhabit the steppes, semi-deserts and mountain meadows with dense grasses. They feed on grass and seeds. Due to the dense grass cover, the rapid movement of these small animals is difficult. But they also do not have the need to make long feeding trips, since food is abundant in their habitats almost everywhere. They live in permanent burrows, where they rest, breed, and most species in burrows lie down for summer and winter hibernation. Due to the abundance of food, they do not go far from the hole. Often they build additional, so-called fodder, holes, which serve as a temporary shelter from the danger that appeared during feeding. They run slowly. The body is valky, on short legs, well adapted for locomotion in burrows. Due to the presence of underground nests, they give birth to blind, naked, helpless cubs.
The described group, in addition to ground squirrels, includes marmots, hamsters and steppe types of haystacks.
Among terrestrial mammals there are a number of species that cannot be assigned to any of these diverse groups. These are widespread animals that live in various living conditions and do not have a narrow specialization. Such are many predators, for example, a wolf, a fox, a badger, partly a wild boar, etc. Suffice it to point out that the wolf and the fox live in the tundra (the latter only in its southern parts), in the forest, steppe, desert, and mountains. The composition of food, the nature of its obtaining, the conditions of reproduction are different in connection with the conditions of existence. For example, wolves in the forest belt whelp on the surface of the earth in a den, and sometimes dig holes in the desert and tundra.
II. Underground mammals are a small highly specialized group of species that spend all or a significant part of their life in the soil. Its representatives are found in different units. Such, for example, are numerous species of moles from the order of insectivores, mole rat, zokor, mole voles from the order of rodents, marsupial mole and some others. They are distributed in various parts of the world: in Eurasia (moles, zokors, mole rats, mole voles), in North America (moles), in Africa (golden mole), in Australia (marsupial mole).
The laying of underground passages is carried out differently in different species. The mole destroys the earth with its front paws turned outward and, acting with them like spoons, pushes it to the side and back. Outward, the earth is thrown out by the front part of the body through vertical otnorki. Forepaws digs zokor. The mole rat and the mole voles have weak paws with small claws; they dig the soil with incisors far protruding from the mouth, mainly the lower ones, and throw the earth out with the front part of the body, like a mole and zokor (mole rat), or with their hind legs (mole voles). In these rodents, the incisors are, as it were, outside the mouth, since behind the incisors there is a fold of skin that can completely isolate the mouth from the incisors. In mole rats, as B. S. Vinogradov showed, the lower jaw can occupy a different position. When feeding, the position of the jaws is normal and the lower incisors rest against the upper ones. When digging, the lower jaw retracts and the exposed incisors can be used like a hoe to break up the earth.
III. Water animals. As in the previous case, there is a long series of transitions from terrestrial to entirely aquatic species. A particularly clear picture is given by carnivores, which are phylogenetically closest to one of the groups of aquatic mammals - to pinnipeds. Initially, a partial connection with the aquatic environment lies in the fact that animals get food not only on land, but also near water or in the water itself. So one of the species of our ferrets - mink lives along the banks of fresh water. She settles in a hole, the exit from which often opens onto land. It feeds on rodents living near the water (mainly water rats (15-30%), amphibians (10-30%) and fish (30-70%). The mink swims well, but it has no significant changes in the coat and limbs. To a greater extent, the otter is associated with water. It arranges holes only along the banks of reservoirs and has an entrance from them under water. The otter usually does not leave the coast further than 100-200 m. (10-20%). Terrestrial rodents are of little importance. The limbs of the otter are shortened, the fingers are connected by a wide membrane. The auricles are very small. The coat consists of a rare awn and dense low underfur. The sea otter (sea otter) is a real sea animal that lives in the northern part of the Pacific Ocean spends most of its life in the water, where it gets all the necessary food (sea urchins, molluscs, crabs, less often fish). Otters are often on the shore.They swim very well, in calm weather they swim tens of kilometers from the shore. No dwellings on the shore are satisfied. The limbs are short, like flippers; all fingers are united by a thick membrane. The claws are rudimentary. There are no auricles. Coat of sparse awn and dense underfur.
Many semi-aquatic species among rodents. Such are the beaver, muskrat, nutria. All of these species are associated with water as the main source of food, but partly forage on land. In the water, they are also saved from the persecution of enemies. They nest in earthen burrows or in huts, which are built on the shore or on the floating remains of rotting vegetation. All these animals do not have an auricle, their paws have membranes. The coat, like that of other semi-aquatic animals, with a rare stiff awn and thick underfur. The muskrat, muskrat, and beaver have strongly developed sebaceous glands, which apparently perform a role similar to that of the avian oil gland.
Pinnipeds are already almost completely aquatic animals. They feed exclusively in the water, and usually rest on the water. They only have puppies, mating and molting outside the water - on the shore or on the ice. There are many unique features in the building. The general shape of the body is spindle-shaped, the limbs are turned into flippers. At the same time, the hind flippers are far pushed back; in most species, they do not take part in moving along a solid substrate. The hind flippers serve as the main locomotor tool when swimming and diving. The coat is reduced to some extent, and the function of thermal insulation is performed by a layer of subcutaneous fat. It should be noted that in eared seals (for example, in a seal), which are most associated with land, the coat is still quite good, and the subcutaneous layer of fat, on the contrary, is poorly developed. Our flying squirrel also retains a rudimentary auricle.
In conclusion, it must be emphasized that the aquatic environment is secondary for mammals. Being originally terrestrial animals, they were able to adapt to it in one way or another.
IV. Flying animals undoubtedly evolved from forest animals by developing the ability to jump, then to glide, and only ultimately to flight. This series can be seen in the review of modern species. When jumping, our squirrel spreads its paws wide, increasing the plane of the body supported by air. She does not yet have flight membranes. The Australian has small flying membranes that reach to the hand. In our flying squirrel and the South Asian winged wing, the membrane stretches along both sides of the body between the front and hind legs. These animals can "fly" for tens of meters.
The only real flying animals are bats or bats. They have a number of features close to those of birds. So, the sternum carries a keel that serves to attach the flying (pectoral) muscles. The chest becomes more durable, which is associated with the fusion of some of its elements. The bones of the skull are fused. In connection with the nocturnal lifestyle, the organs of hearing and touch are more developed.
The essay above environmental groups mammals is not exhaustive. His task is to show the variety of adaptations of animals of this class in a variety of living conditions.
Nutrition. The food composition of mammals is extremely diverse. At the same time, they get food in various living environments (air, earth's surface, soil thickness, surface and water column). These circumstances serve as one of the most important prerequisites for the species diversity of mammals and their wide distribution. According to the type of food, mammals can be divided into two conditional groups: carnivores and herbivores. The conditionality of this division is determined by the fact that only a few species feed exclusively on animals or exclusively on plants. Most feed on both plant and animal food, and the specific value of these feeds can vary significantly depending on the conditions of the place, season, and other reasons.
The initial type of food for mammals, apparently, was insectivorous. The simplest Mesozoic mammals obviously (judging by the nature of their teeth) fed mainly on terrestrial, partly arboreal insects, molluscs, worms, as well as small amphibians and reptiles. This type of diet has been preserved by the most primitive modern groups, namely: many species of the insectivorous order (primarily shrews, tenrecs, and partly hedgehogs) and some species of marsupials. They collect their food mainly from the surface of the earth, in shallow burrows.
Along with the group of insectivores described above, branches that were more specialized in nutrition also arose. These are the majority of bats that feed on insects in the air, anteaters, lizards, aardvarks, and of the monotremes, echidnas that feed on termites, ants and their larvae, which they get using special devices (an elongated snout, a long sticky tongue, strong claws that serve to destruction of insect nests, etc.). Undoubtedly, moles are specialized insectivores, since they get all their food in the thickness of the soil.
Species of animals that are biologically predators belong mainly to the orders of carnivores, pinnipeds and cetaceans.
Phylogenetically, they are close to insectivores and represent branches of one common root that have switched to eating more than big booty, partly warm-blooded vertebrates. Only a few species of this group are entirely carnivorous: such are cats, polar bears. Most of them feed on plant foods to some extent.
The importance of plant foods in the diet of brown and black bears is especially great. Very often they long time they feed only on berries, nuts, fruits of wild trees and animal food is obtained as an exception. This happens, for example, with Caucasian, Central Russian bears.
Most species of carnivores feed on carrion. Definitely avoid eating cat carrion. Especially often carrion is eaten by jackals. Hyenas feed almost exclusively on carrion.
There are a lot of herbivorous animals. These include most monkeys, semi-monkeys, sloths from edentulous teeth, most rodents, ungulates, marsupials, some bats (bats), and from sea animals - sirens. According to the nature of food, they can be divided into herbivores, feeding on leaves and branches, granivorous and frugivorous. This division is to a certain extent arbitrary, since many species often feed on one or another food, depending on environmental conditions.
Typical herbivorous animals are horses, bulls, goats, rams, some deer and many rodents. In ungulates, adaptation to feeding on grass is expressed in the strong development of fleshy lips and tongue and their great mobility, in the form of teeth and in the complication of the intestinal tract. In connection with feeding on soft grass, the upper incisors in artiodactyls are reduced. Horses grazing in the steppes and deserts with tougher vegetation retain their upper incisors. Rodents capture grass not with their lips, like ungulates, but with their incisors, which are especially highly developed in them. Such are nutria, muskrats, and voles. All herbivores are characterized by an increase in the volume of the intestine (in ruminants - by complicating the stomach, in rodents - by a strong development of the caecum).
Moose, deer, giraffes, elephants, hares, beavers, sloths feed on branches, bark and leaves. Most of these species also eat grass. Most often, branch fodder and bark are consumed in winter, grass - in summer.
Many of the herbivorous animals feed mainly on seeds. These are squirrels, whose nutritional well-being depends on the presence of conifer seeds, chipmunks, which, in addition to coniferous seeds, eat a lot of seeds of cereals and legumes, mice, which, unlike voles, eat relatively little grass. Seed-eaters are relatively limited in their food supply, and their success often depends on the yield of seeds from a few plant species. Crop failures of such fodder entail mass migrations of animals or their death. So, for example, our squirrel in the years of poor harvest of conifers is forced to eat their kidneys, which are rich in resin. The teeth and mouth of such animals are often completely covered with resin.
There are relatively few specialized fruit-eaters. These include some monkeys, half-monkeys, fruit bats, among your rodents - a dormouse. Some tropical bats feed on the nectar of the flowers.
Many species of animals have the ability to use a very wide range of food and successfully adapt to the geographical, seasonal and annual characteristics of food conditions. So, the reindeer in summer feeds mainly on green vegetation, and in winter - almost exclusively on lichens. The white hare feeds on branches and bark only in winter, in summer it eats grass.
The nature of nutrition also varies depending on the conditions of the place. So, brown bears of the South Caucasus are herbivorous, and on the coast of the Far East they feed almost exclusively on fish and seals.
Many examples of this nature can be cited. They speak of the great breadth of mammalian feeding habits. At the same time, they show how important it is to have accurate data on animal nutrition. Only such materials make it possible to judge the economic significance of a particular species.
The amount of food eaten depends on its calorie content. ( and greater or lesser ease of digestion. In this regard, herbivorous animals consume somewhat more food (by weight) than carnivores.
In addition, we point out that when comparing similar indicators for herbivorous species (small-sized species are given earlier), the daily food intake (g of food per g of body weight) of a bull weighing 181,600 g is 0.03, and an African elephant weighing 3,672,000 g is 0. 01. All these examples once again demonstrate the dependence of metabolic rate on body size.
Reproduction. Systematizing the main features of mammalian reproduction, three main options should be distinguished.
1. The laying of an “egg” fertilized inside the mother’s body, followed by the completion of its development in the nest (platypus) or in the leathery bag of the parent (echidna). The eggs in this case are relatively rich in protein and, therefore, relatively large (10-20 mm), with a developed liquid protein coat. The number of simultaneously maturing eggs in the echidna is 1, in the platypus - 1-3.
It should be noted that the term "egg" in the two cases cited above does not fully reflect the essence of the phenomenon. This is due to the fact that in echidna and platypus, fertilized eggs linger in the genital tract for a considerable time and pass most of their development there.
2. The birth of underdeveloped live babies that develop in the uterus, without the formation of a real placenta. A very underdeveloped newborn is firmly attached to the nipple, which often opens into the cavity of the brood leathery pouch, which appears on the female's belly at the time of reproduction. In the bag, the cub is carried, which does not suckle on its own, but swallows the milk injected into its mouth by the female. The described type of reproduction is characteristic of marsupials.
3. The birth of well-developed young, which, in any case, can suckle milk on their own, and in many species can move more or less perfectly. Complete uterine development is due to the appearance of a placenta in these species, hence the name of the described group - placental mammals.
In marsupials, the eggs are small (0.2 - 0.4 mm), poor in yolk; -liquid protein shell is poorly developed. In most species, units of eggs develop simultaneously, and only in opossums - sometimes more than 10.
Placental eggs are very small (0.05 - 0.2 mm), practically devoid of yolk. There is no protein shell. In most species, several eggs ripen at the same time (up to 15-18).
Features of reproduction in different groups of mammals have a clearly expressed adaptive character and are associated with the characteristics of living conditions. This can be clearly seen in the example of the main subclass of mammals - placentals, which, as you know, live in an extremely diverse life environment.
The duration of pregnancy is significantly variable, and in this regard, the degree of development of newborns. In turn, this is related to the conditions in which childbirth occurs. Many species of rodents give birth in specially constructed nests, in burrows, in trees or in grass. Their cubs are more or less completely protected from harmful action climatic factors and predators. These species have a short pregnancy, and their newborns are helpless, naked, blind. So, in a gray hamster, pregnancy is 11-13 days, in a house mouse - 18-24, in a gray vole - 16-23 days. In a large muskrat, pregnancy lasts only 25-26 days, in marmots - 30-40 days, in squirrels - 35-40 days. Comparatively short pregnancy is also observed in canine species born in burrows. So, in the arctic fox it is 52-53 "days, in the fox - 52-56 days. A much longer pregnancy is observed in species that give birth to cubs in primitive nests or in dens. So, in nutria it is 129-133 days, in a leopard - 4 months, a leopard - 3 months. An even longer period of embryonic development in animals that give birth to cubs on the surface of the earth and in which newborns, due to the conditions of existence, are forced to follow their mother in the first days after birth. Such are ungulates. Reindeer pregnancy lasts 8-9 months, and even in small antelopes, goats and rams it lasts 5-6 months.It is significant that the most well-developed (from among land animals) cubs are born in horses (horses, donkeys, zebras), i.e. i.e. in species living in open steppe-desert spaces.Cubs in them can follow their mother in a few hours.Pregnancy in these animals lasts 10-11 months.
Of course, it must be borne in mind that the duration of pregnancy is also associated with the size of the animals, but nevertheless the figures given, and most importantly, the degree of development of newborns, clearly confirm the position that the duration of embryonic development has an adaptive value. This can also be demonstrated by comparing closely related species living in different conditions. Hares do not make nests and kittens on the surface of the earth. Their pregnancy lasts 49-51 days, the cubs are born sighted, covered with fur and capable of running already in the first days of life. Rabbits live in burrows where they give birth to their young. The pregnancy of rabbits is 30 days, their newborns are helpless - blind and naked.
Particularly illustrative examples are given by aquatic mammals. Seals give birth on land or on ice, and their young (in most species) lie without any cover. They are born after 11-12 months of embryonic development well formed, sighted, in thick wool. Their sizes are equal to 25-30% of the size of the mother. A very long pregnancy and the large size of the cubs, allowing them to lead an independent lifestyle, characteristic of whales, in which the act of childbirth takes place in the water.
The speed of reproduction in different species of mammals is very different. This is due to the length of time it takes to reach puberty, the size of the interval between two births, and finally, the size of the brood. Large animals reach maturity relatively late. So, in elephants it happens at the age of 10-15 years, in rhinos - 12-20 years, in different types of deer - 2-4 years; male seals become sexually mature in the third or fourth year, females in the second or third year; in the third or fourth year, bears, many seals, and tigers become capable of breeding. Species of dogs and martens gain the ability to reproduce more quickly - in the second or third year of life.
Especially precocious rodents and hares. Even large species, such as hares, breed in the next summer of life, that is, at an age of somewhat less than a year. The muskrat starts breeding at the age of 5 months. Small mouse-like rodents mature even faster: house mouse - at the age of 21/a months, field and forest mice - 3 months, and voles at the age of 2 months.
The frequency of childbearing and the size of the brood are different. Elephants, baleen whales, walruses, tigers breed every 2-3 years and usually bring one cub. Every year, dolphins and bovid deer are born, which also bring one cub each. Canine, mustelid and large species of cats, although they breed once a year, their fertility is noticeably greater, since they give birth to several cubs. So, in a litter, lynxes have 2-3 (rarely more) cubs, sables, martens, ferrets - 2-3, wolves - 3-8 (up to 10), foxes - 3-6 (up to 10), arctic foxes 4-12 (up to 18).
Rodents and lagomorphs are especially prolific. Hares bring in a year 2-3 litters of 3-8 (up to 12) cubs; squirrels - 2-3 litters of 2-10 cubs, voles - 3-4 litters per year of 2-10 cubs. If we take into account that voles become sexually mature at the age of two months, then the enormous speed of their reproduction will become clear.
The speed of reproduction is related to the life expectancy and the rate of death of individuals. How general rule, long-lived species reproduce more slowly. So, elephants live 70-80 years, bears, large cats - 30-40 years, canine species - 10-15 years, mouse-like rodents - 1-2 years.
The rate of reproduction varies significantly over the years, which is associated with changes in living conditions. This is especially noticeable in species with high fecundity. So, in years with favorable food and meteorological conditions, squirrels bring 3 litters of 6-8 (up to 10) cubs, and in difficult years, when females are exhausted, the number of broods is reduced to 1-2, and the number of cubs in a brood - up to 2- 3 (maximum 5). The percentage of barren females also varies. As a result, the rate of reproduction is sharply reduced. A similar picture is also characteristic of other animals, such as hares, muskrats, and mouse-like rodents.
Fertility changes with age. So, the percentage of pregnant women in the Alaskan cat turned out to be as follows: at the age of 3-4 years - 11%, 5 years - 52%, 7 years - 78%, 9 years - 69%, 10 years - 48%.
Geographical variability is characteristic of many species, we will give one example in relation to the long-tailed ground squirrel.
Most of the information of this kind demonstrates an increase in species fertility in the direction from south to north. It is noteworthy that such a dependence is found in some species when comparing the fecundity of populations living in mountainous countries at different heights. An example is the American deer mouse from Colorado and California. At an altitude of 3.5-5 thousand feet, the average brood size was 4.6; at an altitude of 5.5-6.5 thousand feet, 4.4; 10.5 thousand feet - 5.6.
It is believed that the increase in fertility to the north, and in mountainous countries - upwards, is associated with increased mortality, which is to some extent compensated by an increase in the birth rate.
Among mammals, there are species both monogamous and polygamous. In monogamous species, pairs are formed, as a rule, only for one breeding season. This happens with arctic foxes, often with foxes and beavers. More rare cases of couples for several years (wolves, monkeys). In monogamous species, both parents usually take part in raising the young. However, in some true seals, pairs form only for the period of copulation, after which the male leaves the female.
Most animals are polygamous. These are eared seals, for example seals, whose males during the mating period gather 15-80 females around them, forming the so-called harems. Deer, donkeys, horses, forming schools, consisting of one male and several females, can also serve as an example of polygamous animals. Polygamous and many rodents and insectivores. However, these animals of harems do not form stocks when walking. This is understandable, since they mate several times a year, and their periods between births are usually short.
The mating period for different species falls on very different dates. So, for wolves and foxes, mating occurs at the end of winter, for minks, ferrets, hares - at the beginning of spring, for sables, martens, wolverines - in the middle of summer, for many ungulates - in autumn. In the process of evolution, the period of childbearing and raising young people turned out to be timed to; favorable season for this - usually this is the end of spring and the first half of summer. It is curious that this is characteristic of very diverse species, including those in which the mating period falls on completely different seasons of the year (spring, summer, autumn). In this regard, the duration of pregnancy varies within very large limits (outside of the dependence mentioned above). So, in an ermine pregnancy lasts 300-320 days, in a sable - 230-280 days, in a mink - 40-70 days, and in a wolf - 60 days. A very long pregnancy in such small animals as ermine and sable is due to the fact that the fertilized egg, after a very short development, falls into a dormant state that lasts most of the winter. Only at the end of winter does egg development begin again. Thus, the actual period of development in these animals is short.
The annual cycle of life consists of a number of successive phases, the reality of which is determined by natural seasonal changes in the natural environment and the fact that animals experience different needs at different periods of life. In any phase of the annual cycle, only certain phenomena in the life of the species are dominant.
1. Preparation for reproduction associated with the maturation of reproductive products, characterized primarily by the search for individuals of the opposite sex. In many polygamous species, it ends with the formation of harems. Monogamous species form pairs. In the formation of pairs or harems, chemical (smell) signaling is dominant. Through it, the sexual cycle is synchronized, the species, sex, age, readiness for copulation, the hierarchical position of the oncoming individual in the population, its belonging to its own or someone else's population are identified.
Places are chosen that are especially favorable for the hatching of young ones. In this regard, some species undertake long-distance (hundreds and even thousands of kilometers) migrations. This happens with some bats, whales, most pinnipeds, tundra-reindeer, arctic foxes and a number of other species.
2. The period of childbearing and rearing of young animals is characterized by the fact that at this time even widely migratory species become sedentary. Many predators (brown bears, sables, martens, foxes, arctic foxes, wolves) and rodents (squirrels, flying squirrels, many voles, mice, etc.) occupy nesting areas, the boundaries of which are marked with odor or visual marks. These areas are, as far as possible, protected from invasion by other individuals of their own species or competitive species.
The duration of the lactation period varies widely. Hares already after 7-8 days begin to eat grass, although they also suck mother's milk at the same time. In muskrat, the period of milk feeding lasts approximately 4 weeks, in the wolf - 4-6 weeks, in the arctic fox - 6-8 weeks, in the brown bear - about 5 months, in the mountain barai - 5-7 months. These differences are determined by a number of circumstances: the nature of the food that young people switch to and its quality, the general type of behavior of young people and their parents, the chemistry (nutrition value) of milk, and in this regard, the growth rate of young people.
The duration of the existence of the family in most species is less than a year. In ground squirrels, young ones settle at the age of 1 month, for about the same short time there are broods in hares and squirrels; fox broods break up at the age of 3-4 months young, fox broods - somewhat earlier, which is associated with a low supply of nesting area with food. There are broods of wolves much longer - 9 - 11 months. The bear often lies in the den along with the young. Marmots and raccoons winter in families. The tigress walks with the young until the next estrus, which happens once every 2-3 years. Deer have been walking with their mothers for more than a year.
3. The period of preparation for winter is characterized by molting of animals and intensive feeding. Many animals get very fat. Animals that are not tied to a permanent home move widely, choosing places that are richest in food. We, in middle lane, bears visit berry fields and oat crops. Wild boars also come out to the grain fields. Increasing fatness is an important adaptation for enduring winter conditions. So, in spring, a small ground squirrel has a mass of 140-160 g; and in the middle of summer - 350-400 g. The mass of a raccoon dog in summer is 4 - 6 kg, in winter - 6 - 10 kg. Sonya-shelf gets fat by the end of summer so much that the amount of fat is equal to 20% of the total mass.
It has recently become known that hare hares in the northern parts of the tundra undertake migrations to the south in autumn, and in the opposite direction in spring. Many mountain animals in the summer rise up to the alpine meadows, where there is a lot of food and little food. blood-sucking insects. In winter, they descend to the lower mountain belts, where the depth of the snow cover is less and where it is easier to get food at this time. Such, for example, are the seasonal migrations of wild boars, deer, elk, wild sheep and roe deer. In the Urals, roe deer move in winter from the deep snowy western slope to the eastern one, where the snow cover is always less deep. When snow falls, forest cats, foxes and wolves descend into the foothills with little snow. Vertical migrations of lynxes, tigers, snow leopards have been noted.
Desert ungulates also have seasonal migrations. Goitered gazelles, for example, move from the deserts to the foothills in autumn, where food is better preserved. In the spring they return to the interior. Saiga in Kazakhstan in the summer stays more often in the northern clayey semi-deserts; by winter, it migrates to the south, to the area of less snowy sagebrush-fescue and sagebrush-saltwort semi-deserts.
Some bats from the taiga belt, mixed forests, and even forest-steppes both in Eurasia and North America fly to warmer regions for the winter.
: Although a number of other examples of migrations as adaptations to seasonal changes in living conditions can be cited, in general they are much less developed in mammals than in fish and birds.
Hibernation is widespread among mammals, although it is characteristic of species of only some orders: monotremes, marsupials, insectivores, bats, edentulous, predatory, rodents.
According to the degree of depth of hibernation, three types can be distinguished.
1. Winter sleep, silt, and optional hibernation, is characterized by a slight decrease in the level of metabolism, body temperature and respiratory phenomena. It can easily be interrupted.
The conditions under which winter sleep is carried out are different in different species. Brown bears sleep in shallow earthen caves, under a fallen tree, under a bush. Black bears and raccoons usually lie in the hollows of standing trees, raccoon dogs - in shallow holes or in a pile of hay. The burrow of badgers is more complex.
The duration of winter sleep varies from year to year. Numerous cases are known when raccoon dogs, raccoons, during prolonged thaws, come out of holes and hollows and lead an active lifestyle.
2. Real hibernation, periodically interrupted, is characterized by a state of rather deep torpor, a decrease in body temperature, a noticeable decrease in the frequency of breathing, but with the ability to wake up and stay awake for a short time in the middle of winter, mainly during strong thaws. Such hibernation is characteristic of hamsters, chipmunks, and many bats.
True continuous seasonal hibernation is characterized by an even stronger torpor, a sharper drop in temperature and a decrease in respiratory rate. Such hibernation occurs in hedgehogs, some species of bats and marmots, ground squirrels, jerboas, dormouse.
For mammals in the state of hibernation, not only a decrease in the frequency of breathing is characteristic, but also a great irregularity of it: after 5-8 breaths, there is usually a pause of 4-8 minutes, when the animal does not make respiratory movements at all.
Although during hibernation, the metabolism drops sharply, but still does not completely stop, animals exist by spending the energy reserves of their bodies, while losing in mass.
Not in all cases the expense is so large. Groundhogs have been repeatedly observed waking up from hibernation with fat deposits still quite noticeable.
Real hibernation happens not only in winter, but also in summer. This is especially true for gophers. So, even such a relatively northern species of ground squirrels as speckled hibernates already in August. The small ground squirrel in semi-desert areas hibernates already in July. The earliest hibernation occurs in the yellow ground squirrel in Central Asia: in June-July. Summer hibernation usually passes into winter without interruption. A common cause of summer hibernation in ground squirrels is the drying of vegetation, leading to the inability to obtain (along with food) the amount of water necessary for the normal functioning of the body.
It should be borne in mind that real continuous hibernation is based not only on the influence of regularly changing external conditions, but also on the endogenous rhythm of the physiological and biochemical state of the organism.
Among the voles, the root vole, common in the taiga zone, has gained particular fame. In the storerooms of her holes, she collects grains of cereals, less often other grasses and trees, lichen, dry grass, roots. The size of the reserves of this species is significant and can reach 10 kg or more. In other voles, the ability to make stocks is less developed.
Stocks are also made by burrowing rodents. Thus, up to 10 kg of root crops, bulbs, and roots were found in burrows near the zokor. In a mole rat, 4911 pieces of oak roots weighing 8.1 kg, ZSO acorns weighing 1.7 kg, 179 potatoes weighing 3.6 kg, 51 tubers of steppe peas weighing 0.6 kg were found in 5 chambers of one hole - a total of 14 kg.
Some species of rodents store the vegetative parts of plants. A large gerbil living in the deserts of Central Asia cuts grass at the beginning of summer and drags it into holes or leaves it on the surface in the form of piles. This food is used in the second half of summer, autumn and winter. The size of the reserves of this species is measured in many kilograms. Dried grass is stored for the winter by species of pikas, or haystacks. Steppe species pull hay into stacks 35-45 cm high and 40-50 cm in diameter at the base. In forest areas and in the mountains, pikas do not make stacks, but hide the stored hay in cracks between stones or under stone slabs. Sometimes, in addition to grass, they store small branches of birch, aspen, raspberry, blueberry, etc.
River beavers make food supplies for the winter in the form of tree stumps, branches and rhizomes of aquatic plants, which are put into the water near the dwelling. These warehouses often reach large sizes; found stocks of vines up to 20 m3.
Feed stocks are also made by some species that hibernate in winter. Such are hamsters, chipmunks. (Fig. 223) and East Siberian long-tailed ground squirrels. Other gophers do not make stocks. Chipmunks store pine nuts and seeds of cereals and legumes. Stocks in the amount of 3-8 kg are stored in a hole. They are used mainly in the spring after the animals wake up, when there is still little new food. Hamsters also store supplies in burrows. Squirrels dry mushrooms on trees.
Among predatory animals, only a few make large supplies of food. Such, for example, are mink and dark polecat, which collect frogs, snakes, small animals, etc. Sometimes bears, martens, wolverines, and foxes make small food supplies.
population fluctuations. The number of most species of mammals varies greatly from year to year.
Periodically flashing epizootics represent the second main cause of sharp fluctuations in the number of animals. It is curious that epizootics occur more often among species in which the abundance of food is approximately the same over the years. These are hare hares, gerbils, muskrats, water rats, deer, moose. Fluctuations in the number of arctic fox (Fig. 224) are due to both feeding conditions (primarily the number of lemmings) and epizootics
The nature of the epizootic is varied. Worm infestations, coccidiosis, and tularemia are widespread among animals. It is not uncommon for an epizootic to spread simultaneously to several species. This happens, for example, with tularemia. It has been established that diseases not only lead to immediate death, but also reduce fertility and facilitate the pursuit of prey by predators.
For some species, the main reason for population fluctuations is weather anomalies. Deep snow periodically causes mass deaths of wild boars, goitered gazelles, saigas, roe deer and even hare.
The role of predators in fluctuations in the number of animals is different. For many mass species, predators do not serve an important factor population dynamics. They only intensify the process of accelerated extinction of the population, which is due to other reasons. So at least it happens with hares, squirrels, chipmunks, water rats. For slow-breeding ungulates, the damage caused by predators may matter more.
Recently, intrapopulation mechanisms of population regulation have been established. It was found that in a number of rodent species in years of very high population density, the intensity of reproduction is sharply reduced. This is determined by an increase in the proportion of animals that do not breed (first of all, young ones), and in some cases the size of the brood also noticeably decreases. On the contrary, when the population is depressed, the percentage of breeding is high.
Different brood size in years of high and low abundance is a widespread phenomenon. It has also been found in shrews.
Depending on the population level, the rate of puberty changes. So, in the Newfoundland herd of harp seals, with a high number of animals, 50% of females matured by the age of six, and only by the age of eight - all 100%. With a greatly sparse population by fishing, by the age of four, 50% of the females were maturing, and by the age of six, all 100%. Similar differences in the rate of sexual maturation have been noted in a number of other species.
Fluctuations in the number of game animals are manifested with a known regularity. It has been established that changes in the abundance of a species in one direction or another do not simultaneously cover the entire range, but only a larger or smaller part of it. The limits of the spatial distribution of "harvest" or "failure" are determined primarily by the degree of diversity of landscape features of the species range. The more uniform the nature of the place, the greater the space covered by similar changes in the abundance of a given species. On the contrary, in conditions of diverse terrain, the “harvest” has a very variegated, diverse distribution.
Fluctuations in the number of animals are of great practical importance. They have a very negative effect on the results of the extraction of commercial species, making it difficult to plan hunting, harvesting its products, and timely carrying out measures to organize them. Mass reproduction of some animals has a serious negative impact on agriculture and public health (since many rodent species serve as carriers of diseases). In the Soviet Union, extensive research is being carried out on forecasts of mass breeding of animals and on measures to eliminate economically undesirable fluctuations in their numbers.
Practical value mammals
Commercial animals. Of the 350 species of mammals in the fauna of our country, approximately 150 species can potentially serve as objects of commercial and sport hunting or trapping for the purpose of resettlement and keeping in zoos in forest parks. Most of these species are in the order of rodents (about 35), carnivores (41), artiodactyls (20 species), pinnipeds (13 species), insectivores (5 species), hares (5-8 species).
To obtain furs, about 50 species of wild animals are mined, but the basis of fur production is approximately 20 species.
Fur extraction is carried out in our country in all regions, territories and republics. Grouping them geographically, one can see the following picture characterizing the share (as a percentage of all-Union procurements) importance in the extraction of furs of individual parts of Russia:
In addition to fur trade, ungulate hunting is widely developed in our country. About 500-600 thousand heads are shot annually. The marketable yield of meat in this case is about 20 thousand tons. In addition, a lot of hides and medicinal raw materials (deer antlers, saiga horns) are obtained. In general, the production of wild fishery is estimated at about 25 million rubles. The extraction of ungulates is carried out in an organized manner, with special permits.
Marine animal hunting. The extraction of pinnipeds is carried out by our fishing organizations not only in the seas surrounding Russia, but also in international waters. Thus, harp seals are harvested in the area of the Jan Mayen and Newfoundland islands, where in the second half of winter they concentrate on ice for breeding and molting. The amount of production is limited by between--agreements. The state trade of several species of seals in the sea of the Far East is well developed. Limited production of the Caspian seal is carried out on the ice of the northern part of the Caspian Sea. Seal fishing in the seas is carried out from special vessels adapted for navigation in ice. When seals are hunted, lard and skins are used. In some species of seals, such as the harp and Caspian, newborns have thick white fur, and their skins are used as furs. tyutitttttp pppodmshshtyam gptgp and skins ^ In some species of seals, for example, in grenl ^ ndskog? GW°T! Aspian, newborns have thick edible fur, and their skins are used as dudshchina.
Whaling has recently been drastically curtailed based on international agreements. In the southern hemisphere, harvesting in open pelagic waters of all species is prohibited, with the exception of minke whales. Some countries are allowed limited harvesting of a few other species in coastal waters from coastal bases.
In the northern hemisphere, very limited ship fishing for minke whales, gray whales and sperm whales in open waters and harvesting from coastal bases is allowed.
Russian desman- an endemic of our fauna, sporadically distributed in the basins of the Volga, Don and Ural.
Amur And Turin subspecies of the tiger. The first has been preserved in the number of about 190 individuals in the Primorsky and Khabarovsk Territories; the second, previously common along the currents of the Amu Darya, Syr Darya, Ili and other rivers, is not regularly found in the USSR at present. Sometimes comes from Iran and Afghanistan.
Snow Leopard- a very rare species of the highlands of Central Asia and Kazakhstan, partly Western Siberia.
East Siberian leopard distributed in the south of the Far East, where it is very rare.
Cheetah, formerly widespread in the deserts of Central Asia, in recent years it has not been found in the USSR.
monk seal, previously occasionally encountered - off the coast of Crimea, very rarely enters our waters from the coastal Vedas of Turkey and the Balkan Peninsula.
Of the whales, 5 species are included in the Red Book of the USSR, among them are especially rare greenlamdec and blue whales.
Kulan, formerly widespread in Central Asia and Kazakhstan, remained with us. only in the Badkhyz Reserve (south of Turkmenistan). Acclimatized on the island of Barsakelmes (Aral Sea).
Goral preserved only in the southern part of the Sikhotz-Alin ridge (Primorsky Territory). The total number is about 400 animals.
markhor goat also a very rare species that has been preserved in our mountains in the upper reaches of the Amu Darya and Pyanj.
Transcaspian, Turkmen and Bukhara mountain sheep in an extremely limited number have been preserved in the mountains of southern Turkmenistan and in Tajikistan.
37 species and subspecies are assigned to the number of rare animals of our fauna. Among them are 2 species of bats, 2 species of jerboas, red wolf, polar bear, striped hyena, Ladoga seal, native Ussuri spotted deer, a number of subspecies of mountain sheep, dzeren.
In addition to the protection of individual species and subspecies of animals, a wide network of state reserves created in various geographical zones of the country is of great importance.
Reserves carry out not only protective measures of integral natural complexes, but also conduct a large scientific work to study the patterns of their functioning and evolution.
At present, there are about 128 nature reserves in Russia with a total area of more than 8 million hectares.
For example, the Lapland and Wrangel (on the island of the same name) nature reserves are located in the Arctic and Subarctic; in the taiga zone - Pechoro-Ilychsky, Barguzinsky, Altai; in the European center of the country - Oksky, Prioksko-Terrasny; in the Chernozem Center - Voronezh; in the Volga region - Zhigulevsky; in the Volga delta - Astrakhan; in the Caucasus - Caucasian and Teberdinsky; in the deserts of Central Asia - Repetek; in the Tien Shan - Aksu-Dzhabaglinsky and Sary-Cheleksky, in Transbaikalia - Barguzinsky; in the south of the Far East - Sikhote-Alin; in Kamchatka - Kronotsky.
The impact on the fauna is carried out not only by protecting individual species or entire natural complexes, but also by enriching the fauna with new species.
american mink, larger than our domestic one, successfully acclimatized in the Far East, Altai, in some places in Eastern Siberia and the Kama basin.
Ussuri raccoon dog, previously common in our country only in the Primorsky Territory, was settled in many regions of the European part of the USSR. It has been regularly mined for a long time. Moreover, in areas of acclimatization, approximately 3 times more is mined than in its natural range. In the conditions of hunting farms, this species is harmful, destroying unearthly nesting birds, in particular capercaillie, black grouse, hazel grouse. American raccoon, brought to the USSR in 1936-1941, it took root well in Azerbaijan (Zakatalo-Nukhinskaya lowland). In 1949, the capture of this animal for resettlement in other regions of the USSR began. He took root in Dagestan, Krasnodar Territory. The raccoon has also taken root in the walnut forests of the Ferghana Valley (Kyrgyzstan), although its numbers here are very low. The acclimatization of the raccoon is much more successful in the Belarusian "Polesye", where fishing is already possible. The experience of acclimatization in the Primorsky Territory of the Far East turned out to be unsuccessful.
Nutria- a large semi-aquatic rodent common in South America. It was brought to the USSR in 1930. In total, about 6 thousand animals were settled. In a number of cases, the experiments were unsuccessful, since the coypu is not well adapted to living in water bodies, on which an ice cover forms even for a short time. The greatest success was obtained in Transcaucasia. The Kura-Araks lowland of Azerbaijan is currently the main area for commercial production of this species. In addition, in the wild, nutria are found in the southern regions of the republics of Central Asia and the floodplains of the river
bison, preserved in small numbers in Belovezhskaya Pushcha, is reacclimatized in the Caucasian Reserve, where hybrid animals are released.
Noble deer, or deer, acclimatized in the farms of Ukraine, Moscow and Kalinin regions. This event has no commercial value, since the number of acclimatists is small everywhere.
saiga successfully acclimatized on the island of Barsakelmes (Aral Sea). The kulan is also acclimatized there.
A wild boar, originally released in the hunting area of the Kalinin region (Zavidovsky district), settled in the adjacent regions of the Moscow region and in a number of other regions.
Such wonderful animals as brown bear, lynx, wolverine also require careful attitude. The extraction of a polar bear in our country has long been banned.
A number of mammalian species are of significant epidemic importance, since they are the keepers and transmitters of many infectious diseases dangerous to humans. Diseases whose pathogens affect both animals and humans are called anthropozoonoses. These include plague, tularemia, leishmaniasis (pendine ulcer), typhus fevers (rickettsiosis), tick-borne relapsing fever (spirochetoa), encephalitis, and others.
Currently, about 40 thousand species of chordates are known, living in the aquatic, terrestrial and air environment.
The main signs of chordates:
The presence of an internal axial skeleton (in embryogenesis, a chord is laid, which is subsequently replaced by a cartilaginous or bone spine).
Above the chord (dorsally) is the neural tube, which has an internal cavity - the neurocoel. The tubular structure of the nervous system promotes metabolism not only from the surface, but also from the inside, which makes it possible to increase the mass of the brain.
The digestive tube is laid under the chord. In the anterior section (pharynx), the gill apparatus develops in the embryos. In aquatic chordates, gill slits persist throughout life; in terrestrial ones, they are laid down in embryogenesis in the form of pharyngeal pockets, with the first gill sac being transformed into the Eustachian tube of the middle ear; the second is involved in the formation of palatine tonsils; the third, fourth and fifth give rise to the endocrine glands - the thyroid gland, the parathyroid gland.
On the ventral side of the body, ventrally, is the central organ of blood circulation - the heart or a pulsating blood vessel replacing it. The circulatory system is closed.
Aromorphoses:
The appearance of the axial skeleton - chords.
The central nervous system is in the form of a tube, from the front of which the brain is formed.
The presence of gill slits in the walls of the pharynx (provides active gas exchange in aquatic animals when water is pumped by the mouth apparatus through the gill slits).
The spine, the basis of a strong and flexible internal skeleton, is being formed.
In connection with active movement, the tail develops strongly in most aquatic vertebrates, paired limbs appear - pectoral and ventral fins. In terrestrial vertebrates, paired fins evolved into forelimbs and hindlimbs. Paired limbs are absent only in Cyclostomes.
An active lifestyle has led to the complication of the brain, digestive, respiratory and excretory systems, the formation of the jaw apparatus.
With the advent of amniotes, the following aromorphoses appeared: the appearance of special embryonic membranes and dense egg membranes (absent in mammals, with the exception of oviparous ones)
Systematics
The phylum chordata comprises four subtypes:
Subtype Hemichordates. A few animals united in one class - intestinal-breathing. The representative is a balanogloss.
Subtype Larval-chordates, or tunicates. Marine animals of diverse structure and lifestyle. Representatives - ascidians, salps and appendiculars. Their body is enclosed in a shell - a tunic. The tunic is a product of the secretion of skin cells. In terms of chemical composition, it is close to plant fiber (the only example in the animal kingdom). In adults (ascidians) with an attached way of life, the notochord is reduced. All features of chordates have only mobile larvae.
Subtype Cranial (Cyphalochordidae). Modern non-cranial are represented by 20 species of small marine fish-like animals. The representative is a lancelet.
The subtype Cranial, or vertebrates, is divided into two large groups: anamnia and amniotes.
Anamnia, or lower vertebrates, are grouped into three classes based on the following features:
they have gills as respiratory organs;
the development of their embryos occurs in the aquatic environment;
during the development of the egg, embryonic membranes are not formed.
Class Cyclostomes.
Pisces class.
Class Amphibians.
Amniotes, or higher vertebrates, are grouped into three classes based on the following features:
gill breathing is absent;
during development of the egg, embryonic membranes are formed. The development of eggs and embryos in amniotes occurs inside the egg or in the mother's body in special embryonic membranes - amnion, chorion, allantois. The embryonic membranes perform the functions of protection and ensure the metabolism of the embryo. In addition to the embryonic membranes, egg membranes are formed. They additionally provide the developing fetus with the necessary organic and inorganic substances perform protective and respiratory functions.
Class Reptiles.
Bird class.
Class Mammals.
covers represented by leather and its derivatives. The skin is made up of two layers: the epidermis and the corium (dermis). Upper layer, epidermis, ectodermal origin, can be single-layered or multi-layered. The derivatives of the epidermis include fish scales, reptile scales, feathers, hair, wool, nails, claws and other formations. Various glands develop in the epidermis: mucous, sebaceous, sweat, odorous. The dermis is made up of fibrous connective tissue. Origin - mesodermal.
Musculoskeletal system. The internal skeleton is laid down as a chord of endodermal origin, surrounded by a connective tissue membrane. In higher chordates, in ontogenesis, the notochord is replaced by the spine, and the skeleton of the head is formed in the anterior part. In adult vertebrates, the notochord is preserved only in cyclostomes and some lower fish. The skeleton of the head consists of the brain and facial (visceral) sections, the latter includes the gill arches and their derivatives. Fish already have jaws (from gill arches). Vertebrates are characterized by the development of two pairs of limbs. The muscular system is represented by smooth and striated muscles. The lower ones have a segmental structure, while the higher ones have no segmentality. In connection with the appearance of the jaws and limbs, a mobile type of bone connection is formed - with the help of joints. Muscles responsible for the movement in the joint are antagonists - flexors and extensors.
Digestive system. In cephalochordas in the form of a straight tube and poorly developed digestive glands. In vertebrates, the digestive canal is differentiated into the oral cavity, pharynx, esophagus, stomach, small and large intestines; well-developed glands lying outside the digestive tract - the liver and pancreas. In aquatic forms, the pharynx is pierced by gill slits.
Respiratory system. In lower chordates, it is formed by gills, and in adult amphibians and terrestrial vertebrates, it is formed by lungs that develop from pharyngeal pockets. Part of gas exchange in chordates occurs through the skin.
Circulatory system in all chordates (except tunicates) it is closed. In cephalochords, the heart is absent, in the rest, due to an increase in the intensity of metabolism, the appearance and complication of the heart occurs. In cyclostomes, fish and amphibian larvae, one circle of blood circulation and venous blood enters the two-chambered heart, which then goes through the abdominal aorta to the gills. In adult amphibians, reptiles, birds and mammals, lungs appear and a second circle of blood circulation occurs - pulmonary. In the heart, there are a different number of chambers. Amphibians have two atria and a ventricle, in reptiles in a three-chambered heart an incomplete septum appears in the ventricle, the right and left aortic arches depart from the ventricle. In birds, the septum is complete, only the right aortic arch is preserved, in mammals there is also a four-chambered heart, complete separation of arterial and venous blood, the aortic arch is left.
excretory system. In lancelets - nephridia, in the rest of the chordates - paired kidneys, ureters and bladder. In fish and amphibians at the larval stage, the head kidneys, or pronephros (pronephros), function. They are represented by a large number of excretory tubules that open with funnels (nephrostomas) into the body cavity, the second opening of the tubules opens into the common excretory duct. Next to the nephrostomy capillary glomeruli (Malpighian glomeruli) are located, from which the blood plasma with metabolic products enters the abdominal fluid and then, through the nephrostomy, into the excretory tubules. In adult fish and amphibians, posterior to the pronephros, trunk buds are laid - mesonephros (primary buds). The internal structure differs in that, next to the nephrostomy, an invagination (Bowman's capsule) is formed in the wall of the tubule, in which the capillary glomerulus is found. Such a formation is called the Malpighian body, and together with the excretory tubule - the nephron. In primary kidneys, up to several hundred nephrons. Some nephrons retain contact with the coelom through funnels, while others lose. In reptiles, birds and mammals, secondary kidneys (metanephros, pelvic kidneys) are formed. The renal tubules begin with the Malpighian body, i.e. Bowman's capsule and capillary glomerulus. Reabsorption (reabsorption) of water, vitamins, glucose, amino acids, hormones, salts occurs in the tubules. As a result, the amount of urine excreted decreases, but the concentration of dissimilation products sharply increases in it.
Nervous system subdivided into central and peripheral. The central nervous system is a neural tube with a channel inside (neurocoel) and is located on the dorsal side of the body. The neurocoel is formed by the folding of the ectodermal neural plate. In vertebrates, due to an active lifestyle, the anterior part of the neural tube forms the brain. The brain is laid in the form of three bubbles - anterior, middle and posterior. The anterior differentiates into the anterior and intermediate, the middle remains, and the posterior gives the cerebellum and the medulla oblongata. In the brain there are cavities - cerebral ventricles, connecting with the spinal canal.
The peripheral nervous system is represented by nerve ganglia, craniocerebral and spinal cord nerves extending from the central nervous system. Anamnias have 10–11 pairs of cranial nerves, while amniotes have 12 pairs. The peripheral nervous system is subdivided into the autonomous, or vegetative, which regulates the functioning of internal organs, and the somatic, which regulates the contraction of skeletal muscles and innervates the skin. The sense organs are well developed.
Sexual system. The sex glands are the testes in males and the ovaries in females, the excretory tracts are the oviducts (female) and the vas deferens. Most chordates are dioecious.
Phylogeny - vertebrates appeared in the Paleozoic era in the Silurian period, in the Devonian period the first amphibians came to land, in the Carboniferous period reptiles appeared. In the Mesozoic era, mammals (animals) and birds appear.
