CLASS Amphibians (AMRNIVIA)

General characteristics. Amphibians - four-legged vertebrates from the group Anamnia. Their body temperature is temperature dependent external environment. Bare skin, big amount mucous glands. The forebrain has two hemispheres. nasal cavity communicates with the mouth through the internal nostrils - choanae. There is a middle ear, in which one auditory ossicle is located. The skull is articulated with a single cervical vertebra by two condyles. The sacrum is formed by one vertebra. The respiratory organs of larvae are gills, while adults are lungs. The skin plays an important role in respiration. There are two circles of blood circulation. The heart is three-chambered and consists of two atria and one ventricle with an arterial cone. Trunk kidneys. They reproduce by spawning. The development of amphibians takes place with metamorphosis. Caviar and larvae develop in water, have gills, they have one circle of blood circulation. Adult amphibians after metamorphosis become terrestrial pulmonary-breathing animals with two circles of blood circulation. Only a few amphibians spend their entire lives in the water, retaining gills and some other signs of larvae.

More than 2 thousand species of amphibians are known. They are widely distributed on the continents and islands of the globe, but are more numerous in countries with a warm, humid climate.

Amphibians serve as valuable objects of physiological experiments. Much has been done in their study. outstanding discoveries. So, I. M. Sechenov discovered the reflexes of the brain in experiments on frogs. Amphibians are interesting as animals phylogenetically related, on the one hand, to ancient fish, and v the other - with primitive reptiles.

Structure and life functions. The appearance of amphibians is varied. In tailed amphibians, the body is elongated, the legs are short, approximately the same length, and a long tail is preserved throughout life. In tailless amphibians, the body is short and wide, the hind legs are jumpy, much longer than the front ones, and the tail is absent in adults. Worms (legless) have a long, worm-like body without legs. In all amphibians, the neck is not expressed or is weakly expressed. Unlike fish, their head is movably articulated with the spine.

Covers. The skin of amphibians is thin, naked, usually covered with mucus secreted by numerous skin glands. In larvae, the mucous glands are unicellular, in adults they are multicellular. The secreted mucus prevents the skin from drying out, which is necessary for skin respiration. In some amphibians, the skin glands secrete a poisonous or burning secret that protects them from predators. The degree of keratinization of the epidermis in different types amphibians are far from the same. In larvae and those adults that lead a mainly aquatic lifestyle, keratinization of the surface layers of the skin is poorly developed, but in toads on the back the stratum corneum makes up 60% of the entire thickness of the epidermis.

The skin is an important respiratory organ in amphibians, as evidenced by the ratio of the length of skin capillaries to the length of these vessels in the lungs; in the newt it is 4:1, and in toads, which have drier skin, it is 1:3.

The coloration of amphibians is often protective. Some, like the tree frog, are able to change it.

The skeleton of amphibians consists of the spine, skull, bones of the limbs and their belts. The spine is divided into sections: cervical, consisting of one vertebra, trunk - from a number of vertebrae, sacral - from one vertebra and tail. In tailless amphibians, the rudiments of the caudal vertebrae fuse into a long bone - the urostyle. In some tailed amphibians, the vertebrae are biconcave: remnants of the notochord remain between them. In most amphibians, they are either convex in front and concave in the back, or, conversely, concave in the front and convex in the back. The chest is absent.

Scull mostly cartilaginous, with a small number of overhead (secondary) and main (primary) bones. With the transition from gill breathing of aquatic ancestors of amphibians to pulmonary respiration, the visceral skeleton changed. The skeleton of the gill region has partially changed into the hyoid bone. The upper part of the hyoid arch - pendants, to which the jaws are attached in lower fish, in amphibians, due to the fusion of the primary upper jaw with the skull, has turned into a small auditory bone - a stirrup located in the middle ear.

Skeleton limbs and their belts consists of elements characteristic of the five-fingered limbs of terrestrial vertebrates. The number of toes varies across species. . musculature amphibians, due to more diverse movements and the development of limbs adapted to movement on land, to a large extent loses its metameric structure and acquires greater differentiation. The skeletal muscles are represented by many individual muscles, the number of which in a frog exceeds 350.

nervous system has undergone significant complications compared to that of fish. The brain is relatively larger. The progressive features of its structure should be considered the formation of the forebrain hemispheres and the presence of nerve cells not only in the side walls, but also in the roof of the hemispheres. Due to the fact that amphibians are inactive, their cerebellum is poorly developed. The diencephalon from above has an appendage - the epiphysis, and a funnel departs from its bottom, with which the pituitary gland is connected. The midbrain is poorly developed. Nerves extend from the brain and spinal cord to all organs of the body. There are ten pairs of head nerves. The spinal nerves form the brachial and lumbosacral clutches that innervate the fore and hind limbs.

sense organs amphibians have received progressive development in the process of evolution. Due to the fact that the air environment is less sound-conducting, the structure of the inner ear became more complicated in the hearing organs of amphibians and the middle ear (tympanic cavity) with the auditory ossicle was formed. The middle ear is bounded externally by the tympanic membrane. It communicates with the pharynx by a canal (Eustachian tube), which allows you to balance the air pressure in it with the pressure of the external environment. In connection with the peculiarities of vision in the air, amphibians have undergone changes in the structure of the eyes. The cornea of ​​the eye is convex, the lens is lenticular, there are eyelids that protect the eyes. Organs The sense of smell has external and internal nostrils. The larvae and amphibians permanently living in the water retained the lateral line organs characteristic of fish.

Digestive organs. A wide mouth leads into a vast oral cavity: many amphibians have small teeth on the jaws, as well as on the palate, which help to hold prey. Amphibians have a tongue of various shapes; in frogs, it is attached to the front of the lower jaw and can be thrown out of the mouth; animals use this to catch insects. The internal nostrils, the choanae, open into the oral cavity, and the Eustachian tubes open into the pharynx. Interestingly, in a frog, the eyes take part in swallowing food; having captured the prey with its mouth, the frog, by contraction of the muscles, draws its eyes deep into the oral cavity, pushing the food into the esophagus. Through the esophagus, food enters the bag-shaped stomach, and from there into the relatively short intestine, which is divided into thin and thick sections. The bile produced by the liver and the secretion of the pancreas enter the beginning of the small intestine through special ducts. In the final part of the large intestine - the cloaca - the ureters open, the duct Bladder and genital ducts.

Respiratory system change with the age of the animal. Amphibian larvae breathe with external or internal gills. Adult amphibians develop lungs, although some tailed amphibians retain gills for life. The lungs look like thin-walled elastic bags with folds on the inner surface. Since amphibians do not have a chest, air enters the lungs by swallowing: when lowering the bottom of the oral cavity, air enters it through the nostrils, then the nostrils close, and the bottom of the oral cavity rises, pushing air into the lungs. role played by gas exchange through the skin.

Circulatory system. Amphibians in connection with air breathing have two circles of blood circulation. The amphibian heart is three-chambered, it consists of two atria and a ventricle. The left atrium receives blood from the lungs, and the right atrium receives venous blood from the whole body with an admixture of arterial blood coming from the skin. Blood from both atria flows into the ventricle through a common opening with valves. The ventricle continues into a large arterial cone, followed by a short abdominal aorta. In tailless amphibians, the aorta divides into three pairs of symmetrically outgoing vessels, which are modified afferent branchial arteries of fish-like ancestors. The anterior pair - carotid arteries, carry arterial blood to the head. The second pair - the aortic arches, curving to the dorsal side, merge into the dorsal aorta, from which the arteries depart, carrying blood to various organs and parts of the body. The third pair is the pulmonary arteries, through which venous blood flows to the lungs. On the way to the lungs, large cutaneous arteries branch off from them, heading to the skin, where they branch into many vessels, causing skin respiration, which in amphibians great importance. From the lungs, arterial blood moves through the pulmonary veins to the left atrium.

Venous blood from the back of the body passes partly to the kidneys, where the renal veins break up into capillaries to form the portal system of the kidneys. The veins leaving the kidneys form the unpaired posterior (inferior) vena cava. Another part of the blood from the back of the body flows through two vessels, which, merging, form the abdominal vein. It goes, bypassing the kidneys, to the liver and participates, together with the portal vein of the liver, which carries blood from the intestines, in the formation of the portal system of the liver. Upon leaving the liver, the hepatic veins flow into the posterior vena cava, and the latter into the venous sinus (venous sinus) of the heart, which is an expansion of the veins. The venous sinus receives blood from the head, forelimbs and skin. From the venous sinus, blood flows into the right atrium. Tailed amphibians retain cardinal veins from aquatic ancestors.

excretory organs in adult amphibians, they are represented by trunk kidneys. A pair of ureters depart from the kidneys. The urine they excrete first enters the cloaca, from there - into the bladder. With the reduction of the latter, urine again finds itself in the cloaca, and is released from it. Amphibian embryos have functioning head kidneys.

Reproductive organs. All amphibians have separate sexes. Males have two testes located in the body cavity near the kidneys. The seminiferous tubules, passing through the kidney, flow into the ureter, represented by the wolf channel, which serves to remove urine and sperm. In females, large paired ovaries lie in the body cavity. Ripe eggs enter the body cavity, from where they enter the funnel-shaped initial sections of the oviducts. Passing through the oviducts, the eggs are covered with a transparent thick mucous membrane. The oviducts open into

Development in amphibians takes place with a complex metamorphosis. From the eggs emerge larvae, which differ both in structure and lifestyle from adults. Amphibian larvae are true aquatic animals. Living in the aquatic environment, they breathe with gills. The gills of the larvae of tailed amphibians are external, branched; in larvae of tailless amphibians, the gills are initially external, but soon become internal due to the fouling of their skin folds. The circulatory system of amphibian larvae is similar to that of fish and has only one circulation. They have lateral line organs, like most fish. They move mainly due to the movement of a flattened tail trimmed with a fin.

When a larva turns into an adult amphibian, profound changes occur in most organs. Paired five-fingered limbs appear, tailless amphibians have a reduced tail. Gill respiration is replaced by pulmonary respiration, gills usually disappear. Instead of one circle of blood circulation, two develop:

large and small (pulmonary). In this case, the first pair of afferent branchial arteries turns into carotid arteries, the second becomes aortic arches, the third is reduced to one degree or another, and the fourth is converted into pulmonary arteries. In the Mexican amphibian amblistoma, neoteny is observed - the ability to reproduce at the larval stage, that is, to reach sexual maturity while maintaining larval structural features.

Ecology and economic importance of amphibians. The habitats of amphibians are diverse, but most species stick to wet places, and some spend their entire lives in the water without going to land. Tropical amphibians - worms - lead an underground lifestyle. A peculiar amphibian - the Balkan Proteus lives in the reservoirs of caves; his eyes are reduced, and his skin is devoid of pigment. Amphibians belong to the group of cold-blooded animals, i.e. their body temperature is not constant and depends on temperature environment. Already at 10 ° C, their movements become sluggish, and at 5-7 ° C, they usually fall into a stupor. In winter, in a temperate and cold climate, the vital activity of amphibians almost stops. Frogs usually hibernate at the bottom of reservoirs, and newts - in minks, in moss, under stones.

Amphibians breed in most cases in the spring. Female frogs, toads, and many other anurans spawn into the water, where the males fertilize it with sperm. In tailed amphibians, a kind of internal fertilization is observed. So, the male newt lays sperm clods in mucous sacs-spermatophores on aquatic plants. The female, finding a spermatophore, captures it with the edges of the cloacal opening.

The fecundity of amphibians varies widely. An ordinary grass frog spawns 1-4 thousand eggs in the spring, and a green frog - 5-10 thousand eggs. The development of common frog tadpoles in eggs lasts from 8 to 28 days, depending on the water temperature. The transformation of a tadpole into a frog usually occurs at the end of summer.

Most amphibians, having laid their eggs in the water and fertilizing it, do not show concern for it. But some species take care of their offspring. So, for example, the male midwife toad, widespread in our country, winds the cords of fertilized eggs around its hind legs and swims with it until tadpoles hatch from the eggs. In the female of the South American (Surinamese) pipa toad, during spawning, the skin on the back strongly thickens and softens, the cloaca stretches and becomes an ovipositor. After spawning and fertilization, the male lays it on the back of the female and presses them into the swollen skin with his belly, where the development of the young takes place.

Amphibians feed on small invertebrates, primarily insects. They eat many pests of cultivated plants. Therefore, most amphibians are very useful for crop production. It is estimated that one grass frog can eat about 1.2 thousand insects harmful to agricultural plants during the summer. Toads are even more useful, because they hunt at night and eat a lot of nocturnal insects and slugs that are inaccessible to birds. In Western Europe, toads are often released into greenhouses and greenhouses to exterminate pests. Newts are useful because they eat mosquito larvae. At the same time, it is impossible not to note the harm that large frogs bring by the extermination of juvenile fish. In nature, many animals feed on frogs, including commercial ones.

The class Amphibians is divided into three orders: Tailed amphibians , Tailless amphibians , Legless amphibian .

Detachment Tailed amphibians (Urodela). The most ancient group of amphibians, represented in the modern fauna by about 130 species. The body is elongated, valky. The tail is preserved throughout life. The fore and hind limbs are about the same length. Therefore, tailed amphibians move by crawling or walking. Fertilization is internal. Some forms retain gills for life.

In our country, tailed amphibians are widespread newts(Triturus). The most common are the large crested newt (males are black with an orange belly) and the smaller common newt (males are usually light spotted). In summer, newts live in the water, where they breed, and spend the winter on land in a state of stupor. In the Carpathians you can meet quite a large fire salamander (Salamandra), which is easily recognizable by its black coloration with orange or yellow spots. Giant Japanese salamander reaches 1.5 m in length. To the Proteus family (Proteidea) applies Balkan Proteus, living in the reservoirs of caves and retaining gills all his life. Its skin has no pigment, and its eyes are rudimentary, as the animal lives in darkness. In laboratories for physiological experiments, the larvae of American amblistoms, called axolotls. These animals, like all tailed amphibians, have a remarkable ability to restore lost body parts.

Order Tailless amphibians(Anura) - frogs, toads, tree frogs. They are characterized by a short, wide body. The tail is absent in adults. The hind legs are much longer than the front legs, which determines the movement in jumps. fertilization external,

At lagunis(Ranidae) the skin is smooth, mucous. There are teeth in the mouth. Mostly diurnal and crepuscular animals. At toad (Bufonidae) the skin is dry, bumpy, there are no teeth in the mouth, the hind legs are relatively short. TOwakshi(Hylidae) differ in small size, thin slender body and paws with suction cups at the ends of the fingers. The suction cups make it easier to move through the trees where tree frogs hunt for insects. The color of tree frogs is usually bright green, and may vary depending on the color of the surrounding environment.

Order Legless amphibians(Apoda) -tropical amphibians, leading an underground lifestyle. They have a long, valky body with short tail. In connection with life in minks underground, their legs and eyes have undergone reduction. Fertilization is internal. They feed on soil invertebrates.

Literature: "Course of Zoology" Kuznetsov et al. M-89

"Zoology" Lukin M-89

From educational literature it is known that the skin of amphibians is naked, rich in glands that secrete a lot of mucus. This mucus on land protects against drying out, facilitates gas exchange, and in water reduces friction when swimming. Through the thin walls of the capillaries, located in a dense network in the skin, the blood is saturated with oxygen and gets rid of carbon dioxide. This "dry" information, in general, is useful, but is not capable of evoking any emotions. Only with a more detailed acquaintance with the multifunctional capabilities of the skin does a feeling of surprise, admiration and understanding that amphibian skin is a real miracle appear. Indeed, largely thanks to her, amphibians successfully live in almost all parts of the world and belts. However, they do not have scales, like fish and reptiles, feathers, like birds, and wool, like mammals. The skin of amphibians allows them to breathe in water, protect themselves from microorganisms and predators. It serves as a sufficiently sensitive organ for the perception of external information and performs many other useful functions. Let's consider this in more detail.

Specific features of the skin

Like other animals, the skin of amphibians is an outer cover that protects body tissues from the harmful effects of the external environment: the penetration of pathogenic and putrefactive bacteria (in case of violation of the integrity skin suppuration of wounds occurs), as well as toxic substances. It perceives mechanical, chemical, temperature, pain and other influences due to the equipment with a large number of skin analyzers. Like other analyzers, skin analyzing systems consist of receptors that perceive signal information, pathways that transmit it to the central nervous system, and also analyze this information from higher nerve centers in cerebral cortex. The specific features of the skin of amphibians are as follows: it is endowed with numerous mucous glands that maintain its moisture, which is especially importance for skin respiration. The skin of amphibians is literally riddled with blood vessels. Therefore, oxygen enters directly into the blood through it and carbon dioxide is released; The skin of amphibians is given special glands that secrete (depending on the type of amphibian) bactericidal, caustic, unpleasant, lachrymal, poisonous and other substances. These unique skin devices allow amphibians with bare and constantly moist skin to successfully defend themselves against microorganisms, attacks from mosquitoes, mosquitoes, mites, leeches and other blood-sucking animals. In addition, amphibians, due to these protective abilities, are avoided by many predators; amphibian skin usually contains many different pigment cells, on which the general, adaptive and protective coloration body. Thus, the bright coloration characteristic of poisonous species, serves as a warning to attackers, etc.

Skin respiration

As inhabitants of the earth and water, amphibians are provided with a universal respiratory system. It allows amphibians to breathe oxygen not only in the air, but also in water (although its amount is approximately 10 times less there), and even underground. Such versatility of their organism is possible thanks to a whole complex of respiratory organs for extracting oxygen from the environment where they are at a particular moment. These are the lungs, gills, oral mucosa and skin.

Highest value for the life of most species of amphibians has skin respiration. At the same time, the absorption of oxygen through the skin penetrated by blood vessels is possible only when the skin is moist. Skin glands are designed to moisturize the skin. The drier the surrounding air, the harder they work, releasing more and more new portions of moisture. After all, the skin is equipped with sensitive "devices". They turn on emergency systems and modes of additional production of saving mucus in time.

Different types of amphibians have the same respiratory organs. leading role, others - additional, and still others - may be completely absent. Yes, at aquatic life gas exchange (absorption of oxygen and release of carbon dioxide) occurs mainly through the gills. Gills are endowed with larvae of amphibians and adult tailed amphibians that constantly live in water bodies. And the lungless salamanders - the inhabitants of the land - are not provided with gills and lungs. They receive oxygen and remove carbon dioxide through moist skin and oral mucosa. Moreover, up to 93% of oxygen is provided by skin respiration. And only when individuals need especially active movements, the system of additional oxygen supply through the mucous membrane of the bottom of the oral cavity is turned on. In this case, the share of its gas exchange can increase up to 25%. The pond frog, both in water and in air, receives the main amount of oxygen through the skin and releases almost all carbon dioxide through it. Additional breathing is provided by the lungs, but only on land. When frogs and toads are immersed in water, the mechanisms for reducing metabolism are immediately activated. Otherwise, they would not have enough oxygen.

Helps skin breathe

Representatives of some species of tailed amphibians, for example, the cryptogill, which lives in the oxygenated waters of fast streams and rivers, hardly use their lungs. To extract oxygen from the water, it is helped by the folded skin hanging from the massive limbs, in which there is a net great amount blood capillaries. And so that the water washing it is always fresh, and there is enough oxygen in it, the cryptogill uses expedient instinctive actions - actively mixes the water with the help of oscillatory movements of the body and tail. After all, this constant movement is his life.

The universality of the respiratory system of amphibians is also expressed in the emergence of special respiratory devices in a certain period of their life. So, crested newts cannot stay in the water for a long time and stock up on air, rising to the surface from time to time. It is especially difficult for them to breathe during the breeding season, since when courting females, they perform under water. mating dances. To ensure such a complex ritual, the newt is precisely in mating season an additional respiratory organ grows - a skin fold in the form of a comb. The trigger mechanism of reproductive behavior also activates the body's system for the production of this important organ. It is richly supplied with blood vessels and significantly increases the proportion of skin respiration.

Tailed and tailless amphibians are endowed with an additional unique device for oxygen-free exchange. They are successfully used, for example, by the leopard frog. She can live in an oxygen-deprived cold water up to seven days.

Some spadefoot, a family of American spadefoot, are provided with skin respiration not to stay in the water, but underground. There, buried, they spend most of their lives. On the surface of the earth, these amphibians, like all other anurans, ventilate the lungs due to movements of the floor of the mouth and inflation of the sides. But after the spadelegs burrow into the ground, their lung ventilation system is automatically turned off and skin respiration control is turned on.

A number of features in the structure of the skin of amphibians show their relationship with fish. The integuments of an amphibian are moist and soft and do not yet have such special features adaptive nature, like a feather or hair. The softness and moisture of the skin of amphibians are due to an insufficiently perfect apparatus for breathing, for the skin serves additional body the last one. This feature should have developed already in the distant ancestors of modern amphibians. This is what we actually see; narrowly in stegocephals, the bone skin armor inherited from the ancestors of fish is lost, remaining longer on the belly, where it serves as protection when crawling.
The integument consists of the epidermis and skin (cutis). The epidermis still retains features characteristic of fish: the ciliary cover in larvae, which persists in Auura larvae until metamorphosis; ciliary epithelium in the lateral line organs of Urodela, which spend their whole lives in water; the presence of unicellular mucous glands in larvae and the same aquatic Urocleia. The skin itself (cutis) consists, like in fish, of three mutually perpendicular systems of fibers. Frogs have large lymphatic cavities in their skin, due to which the skin is not connected to the underlying muscles. In the skin of amphibians, especially those that lead a more terrestrial lifestyle (for example, toads), keratinization develops, protecting the underlying layers of the skin from both mechanical damage and drying out, which is associated with the transition to a terrestrial lifestyle. The keratinization of the skin must, of course, impede skin respiration, and therefore greater keratinization of the skin is associated with greater development of the lungs (for example, in Bufo compared to Rana).
In amphibians, molting is observed, i.e., periodic shedding of the skin. The skin is shed as one piece. In one place or another, the skin bursts, and the animal crawls out of it and throws it off, and some frogs and salamanders eat it. Moulting is necessary for amphibians, because they grow until the end of their lives, and the skin would hamper growth.
At the ends of the fingers, the keratinization of the epidermis occurs most strongly. Some stegocephalians had real claws.
Of modern amphibians, they are found in Xenopus, Hymenochirus and Onychodactylus. In the spade toad (Pelobates), a shovel-like outgrowth develops on its hind legs as a device for digging.
Lateral sense organs, characteristic of fish, were present in stegocephalians, as evidenced by canals on the cranial bones. They are also preserved in modern amphibians, namely, they are best preserved in larvae, in which they are developed in a typical way on the head and run along the body in three longitudinal rows. With metamorphosis, these organs either disappear (in Salamandrinae, in all Anura, except for the clawed frog Xenopus from Pipidae), or sink deeper, where they are protected by keratinizing supporting cells. When the Urodela is returned to the breeding water, the lateral line organs are restored.
The skin of amphibians is very rich in glands. The unicellular glands characteristic of fish are still preserved in the larvae of Apoda and Urodela and in the adult Urodela living in the water. On the other hand, real multicellular glands appear here, which developed phylogenetically, apparently from accumulations of unicellular glands, which are already observed in fish.


The glands of amphibians are of two kinds; smaller mucous glands and larger serous, or proteinaceous. The former belong to the group of mesocryptic glands, the cells of which are not destroyed in the process of secretion, the latter are holocryptic, the cells of which are entirely used to form a secret. Protein glands form warty elevations on the dorsal side, dorsal ridges of frogs, ear glands (parotids) in toads and salamanders. Both those and other glands (Fig. 230) are dressed on the outside with a layer of smooth muscle fibers. The secret of the glands is often poisonous, especially the protein glands.
The color of the skin of amphibians is determined, as in fish, by the presence of pigment and reflective iridocytes in the skin. The pigment is either diffuse or granular, located in special cells - chromatophores. Diffuse pigment distributed in the stratum corneum of the epidermis, usually yellow; granular is black, brown and red. In addition to it, there are white grains of guanine. The green and blue coloration of some amphibians is a subjective coloration due to shifting tones in the eye of the observer.
Examining the skin at low magnifications tree frog, tree frogs (Hyla arborea), we see that when looking at the skin from below, it appears black due to the presence of anastomosing and branched black pigment cells, melanophores. The epidermis itself is colorless, but where light passes through the skin with reduced melanophores, it appears yellow. Leukophori, or interfering cells, contain crystals of guanine. Xanthophores contain golden yellow lipochrome. The ability of melanophores to change their appearance, either by rolling into a ball, or by stretching out processes, and determines mainly the possibility of color change. The yellow pigment in xanthophores is mobile in the same way. Leukophores or interfering cells give a blue-gray, red-yellow or silver sheen. Co-op play all these elements will create all kinds of amphibian coloration. Permanent black spots are caused by the presence of black pigment. Melanophores enhance its action. White color caused by leukophores in the absence of melanophores. When the melanophores collapse and the lipochrome spreads, a yellow color will be created. Green color obtained by the interaction of black and yellow chromatophores.
Color changes are dependent on the nervous system.
The skin of amphibians is richly supplied with vessels, serving for respiration. In the hairy frog (Astyloslernus), which has greatly reduced lungs, the body is covered with hair-like outgrowths of the skin, abundantly supplied with blood vessels. The skin of amphibians also serves for the perception of water and for excretion. In dry air, the skin of frogs and salamanders evaporates so profusely that they die. Toads with a more developed stratum corneum survive much longer under the same conditions.

The skin of amphibians is literally riddled with blood vessels. Therefore, oxygen enters directly into the blood through it and carbon dioxide is released; The skin of amphibians is given special glands that secrete (depending on the type of amphibian) bactericidal, caustic, unpleasant, lachrymal, poisonous and other substances. These unique skin devices allow amphibians with bare and constantly moist skin to successfully defend themselves against microorganisms, attacks from mosquitoes, mosquitoes, mites, leeches and other blood-sucking animals.

In addition, amphibians, due to these protective abilities, are avoided by many predators; the skin of amphibians usually contains many different pigment cells, on which the general, adaptive and protective coloration of the body depends. Thus, the bright coloration characteristic of poisonous species serves as a warning to attackers, etc.

As inhabitants of the earth and water, amphibians are provided with a universal respiratory system. It allows amphibians to breathe oxygen not only in the air, but also in water (although its amount is approximately 10 times less there), and even underground. Such versatility of their organism is possible thanks to a whole complex of respiratory organs for extracting oxygen from the environment where they are at a particular moment. These are the lungs, gills, oral mucosa and skin.

Skin respiration is of the greatest importance for the life of most amphibian species. At the same time, the absorption of oxygen through the skin penetrated by blood vessels is possible only when the skin is moist. Skin glands are designed to moisturize the skin. The drier the surrounding air, the harder they work, releasing more and more new portions of moisture. After all, the skin is equipped with sensitive "devices". They turn on emergency systems and modes of additional production of saving mucus in time.

In different types of amphibians, some respiratory organs play a major role, others play an additional role, and still others may be completely absent. So, in aquatic inhabitants, gas exchange (the absorption of oxygen and the release of carbon dioxide) occurs mainly through the gills. Gills are endowed with larvae of amphibians and adult tailed amphibians that constantly live in water bodies. And the lungless salamanders - the inhabitants of the land - are not provided with gills and lungs. They receive oxygen and remove carbon dioxide through moist skin and oral mucosa. Moreover, up to 93% of oxygen is provided by skin respiration. And only when individuals need especially active movements, the system of additional oxygen supply through the mucous membrane of the bottom of the oral cavity is turned on. In this case, the share of its gas exchange can increase up to 25%.

The pond frog, both in water and in air, receives the main amount of oxygen through the skin and releases almost all carbon dioxide through it. Additional breathing is provided by the lungs, but only on land. When frogs and toads are immersed in water, the mechanisms for reducing metabolism are immediately activated. Otherwise, they would not have enough oxygen.

Representatives of some species of tailed amphibians, for example, the cryptogill, which lives in the oxygenated waters of fast streams and rivers, hardly use their lungs. The folded skin hanging from the massive limbs, in which a huge number of blood capillaries are spread out in a network, helps him to extract oxygen from the water. And so that the water washing it is always fresh, and there is enough oxygen in it, the cryptogill uses expedient instinctive actions - actively mixes the water with the help of oscillatory movements of the body and tail. After all, this constant movement is his life.

The universality of the respiratory system of amphibians is also expressed in the emergence of special respiratory devices in a certain period of their life. So, crested newts cannot stay in the water for a long time and stock up on air, rising to the surface from time to time. It is especially difficult for them to breathe during the breeding season, since when courting females, they perform mating dances under water. To ensure such a complex ritual, it is during the mating season that the newt grows an additional respiratory organ - a skin fold in the form of a comb. The trigger mechanism of reproductive behavior also activates the body's system for the production of this important organ. It is richly supplied with blood vessels and significantly increases the proportion of skin respiration.

Tailed and tailless amphibians are endowed with an additional unique device for oxygen-free exchange. They are successfully used, for example, by the leopard frog. She can live in oxygen-deprived cold water for up to seven days.

Some spadefoot, a family of American spadefoot, are provided with skin respiration not to stay in the water, but underground. There, buried, they spend most of their lives. On the surface of the earth, these amphibians, like all other anurans, ventilate the lungs due to movements of the floor of the mouth and inflation of the sides. But after the spadelegs burrow into the ground, their lung ventilation system is automatically turned off and skin respiration control is turned on.

One of the necessary protective features of the skin of amphibians is the creation of protective coloration. In addition, the success of the hunt often depends on the ability to hide. Usually the coloring repeats some specific pattern of the environmental object. So, the coloration with stains in many tree frogs perfectly merges with the background - the trunk of a tree covered with lichen. Moreover, the tree frog is also able to change its color depending on the general illumination, brightness and background color, and on climatic parameters. Its color becomes dark in the absence of lighting or in the cold and brightens in bright light. Representatives of slender tree frogs are easily mistaken for a faded leaf, and black-spotted ones - for a piece of the bark of the tree on which she sits. Almost all tropical amphibians have a protective coloration, often extremely bright. Only bright colors can make the animal invisible among the colorful and lush greenery of the tropics.

Red-eyed tree frog (Agalychnis callidryas)

The combination of coloration and pattern often creates amazing camouflage. For example, a large toad is endowed with the ability to create a deceptive, masking pattern with a certain optical effect. The upper part of her body resembles a lying thin leaf, and the lower part is like a deep shadow cast by this leaf. The illusion is complete when the toad lurks on the ground strewn with real leaves. Could all previous generations, even if numerous, gradually create a body pattern and color (with an understanding of the laws of color science and optics) to accurately imitate a natural counterpart - a browned leaf with a clearly defined shadow under its edge? For this, toads from century to century had to persistently lead their color to the desired goal in order to get the top - brown with dark pattern, and sides - with abrupt change of this color to chestnut brown.

The skin of amphibians has at its disposal wonderful cells - chromatophores. They look like a single-celled organism with densely branching processes. Inside these cells are pigment granules. Depending on the specific range of colors in the coloration of amphibians of each species, there are chromatophores with black, red, yellow and bluish-green pigment, as well as reflective plates. When the pigment granules are collected in a ball, they do not affect the color of the amphibian skin. If, on the other hand, pigment particles are uniformly distributed over all processes of the chromatophore according to a certain command, then the skin will acquire a given color.

The skin of an animal may contain chromatophores containing various pigments. Moreover, each type of chromatophore occupies its own layer in the skin. Different colors of amphibians are formed by the simultaneous action of several types of chromatophores. An additional effect is created by reflective plates. They give the painted skin an iridescent mother-of-pearl luster. Important role in controlling the work of chromatophores along with nervous system hormones play. Pigment-concentrating hormones are responsible for collecting pigment particles into compact balls, and pigment-stimulating hormones are responsible for their uniform distribution over numerous processes of the chromatophore.

And in this gigantic documentation, in terms of information volume, there is a place for a program for our own production of pigments. They are synthesized by chromatophores and are used sparingly. When it is time for some pigment particles to participate in coloring and be distributed over all, even the most distant parts of the spread cell, active work is organized in the chromatophore to synthesize the pigment dye. And when the need for this pigment disappears (when, for example, the background color changes at the new location of the amphibian), the dye is collected in a lump, and the synthesis stops. Lean production also includes a waste disposal system. During periodic molting (for example, in lake frogs 4 times a year), the frogs eat skin particles. And this allows their chromatophores to synthesize new pigments, freeing the body from the additional collection of the necessary "raw materials".

Coloring in some amphibians can change, like chameleons, although more slowly. Yes, different individuals. grass frogs depending on various factors, they can acquire various predominant colors - from red-brown to almost black. The color of amphibians depends on the light, temperature and humidity, and even on emotional state animal. But still main reason changes in skin color, often local, patterned, is "adjusting" it to the color of the background or the surrounding space. For this, the work includes the most complex systems of light and color perception, as well as coordination by structural rearrangements of color-forming elements. Amphibians have been given the remarkable ability to compare the amount of incident light with the amount of light reflected from the background they are in. The smaller this ratio, the lighter the animal will be. When hit on a black background, the difference in the amount of incident and reflected light will be large, and the light of his skin becomes darker.

Information about the general illumination is recorded in the upper part of the retina of the amphibian, and about the illumination of the background - in its lower section. Thanks to the system of visual analyzers, the information received is compared on whether the color of a given individual corresponds to the nature of the background, and a decision is made in which direction it should be changed. In experiments with frogs, this was easily proved by misleading their light perception.

An interesting fact is that in amphibians, not only visual analyzers can control changes in skin color. Individuals completely deprived of sight retain their ability to change body color, "adjusting" to the background color. This is due to the fact that the chromatophores themselves have photosensitivity and react to illumination by dispersing the pigment along their processes. Only usually the brain is guided by information from the eyes, and suppresses this activity of skin pigment cells. But for critical situations the body has a whole system of safety nets so as not to leave the animal defenseless. In this case, too, a small, blind and defenseless tree frog of one of the species, taken from a tree, gradually acquires the color of a bright green living leaf on which it is planted. According to biologists, to a very interesting discoveries can lead to the study of the mechanisms of information processing responsible for chromatophore reactions.

The skin secretions of many amphibians, such as toads, salamanders, and toads, are the most effective weapons against various enemies. Moreover, it can be poisons and unpleasant, but safe substances for the life of predators. For example, the skin of some tree frogs exudes a liquid that burns like nettles. The skin of tree frogs of other species forms a caustic and thick lubricant, and, touching it with the tongue, even the most unpretentious animals spit out the seized prey. The skin secretions of the toads living in Russia emit an unpleasant odor and cause lacrimation, and if it comes into contact with the animal's skin, it causes burning and pain. skin amphibian amphibian fish

Studies of the poisons of various animals have shown that the palm in creating the most powerful poisons does not belong to snakes. For example, the skin glands of tropical frogs produce a poison so strong that it poses a danger to the life of even large animals. From the poison of the Brazilian toad-aga, a dog dies, grabbing it with its teeth. And with the poisonous secret of the skin glands of the South American bicolor leaf climber, Indian hunters lubricated arrowheads. The skin secretions of the cocoa leaf climber contain the poison batrachotoxin, the most powerful of all known non-protein poisons. Its action is 50 times stronger than cobra venom (neurotoxin), several times stronger than the effect of curare. This poison is 500 times stronger than poison holothurian sea cucumber, and it is thousands of times more toxic than sodium cyanide.

The bright coloration of amphibians usually indicates that their skin can release toxic substances. Interestingly, in some species of salamanders, representatives of certain races are poisonous and the most colored. In Appalachian forest salamanders, the skin of individuals secretes toxic substances, while in other related salamanders, skin secretions do not contain poison. At the same time, it is poisonous amphibians that are endowed with a bright color of their cheeks, and especially dangerous ones - with red paws. Birds that feed on salamanders are aware of this feature. Therefore, they rarely touch amphibians with red cheeks, and generally avoid them with colored paws.