What is the skin of amphibians. General covers of amphibians. Learning new material

25.10.2019

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 the outer covering that protects body tissues from harmful influence external environment: penetration of pathogenic and putrefactive bacteria (when the integrity of the skin is violated, suppuration of wounds occurs), as well as toxic substances. It perceives mechanical, chemical, temperature, pain and other influences due to the equipment large quantity 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 of 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 of particular 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; 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.

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 covering.

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 bottom mucosa is turned on oral cavity. 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. 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 cryptobranch uses expedient instinctive actions - it actively mixes the water with the help of oscillatory movements 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, the newt is precisely in mating season grows additional respiratory organ- 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 life. 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.

Specific Features skin

Like other animals, the skin of amphibians is an outer cover that protects the tissues of the body from the harmful effects of the external environment: the penetration of pathogenic and putrefactive bacteria (if the integrity of the skin is violated, 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 the 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 of particular 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; 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.

Skin respiration

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.

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. 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, an additional respiratory organ grows in the newt during the mating season - 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.

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.

vital coloration

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 object. environment. So, the coloration with stains in many tree frogs blends perfectly 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 it sits. Almost all tropical amphibians have patronizing coloration, often extremely bright. Only bright colors can make the animal invisible among the colorful and lush greenery of the tropics.

But how could amphibians develop and gradually dress in protective coloration without knowledge of color science and optics? After all, most often they have such a color when the coloring creates the illusion of a broken continuous surface of the body. At the same time, when joining the parts of the pattern located on the body and legs (when they are pressed against each other), an apparent continuity of the composite pattern is formed. The combination of coloration and pattern often creates amazing camouflage. For example, big toad 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, even if numerous, generations have gradually created the pattern and color of the body (with an understanding of the laws of color science and optics) to accurately imitate the natural counterpart - a browned leaf with a clearly defined shadow under its edge? To do this, from century to century, the toads had to persistently lead their color to the desired goal in order to get the top - brown with a dark pattern, and the sides - with a sharp change in this color to chestnut brown.

How skin creates color?

The skin of amphibians is provided with cells, miraculous in their capabilities - 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. Along with the nervous system, hormones play an important role in controlling the work of chromatophores. Pigment-concentrating hormones are responsible for the collection of pigment particles into compact balls, and pigment-stimulating hormones are responsible for their uniform distribution over numerous processes of the chromatophore.

And how is your own production for the manufacture of pigments carried out? The fact is that the body creates all the most complex macromolecules and other substances in a miraculous way for itself. He quickly and confidently, as it were, "weaves" from the air, light and from the necessary elements supplied to him in time - his own body. These elements are absorbed through the digestive system, inhaled, diffuse through the skin. For this "weaving industry" in focal point each cell and in the control system of the whole organism there is a comprehensive genetic "documentation". It includes a huge databank and program of actions for each molecule, molecular complexes, systems, organelles, cells, organs, etc. up to the whole body. And in this gigantic documentation in terms of information volume there is a place for the program own production pigments. They are synthesized by chromatophores and are used sparingly. When the time has come 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".

Ability to perceive light and color

Coloring in some amphibians can change, like chameleons, although more slowly. So, different individuals of common frogs, depending on various factors, can acquire different predominant colors - from red-brown to almost black. The color of amphibians depends on the light, temperature and humidity, and even on the emotional state of the 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. To do 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 against 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 part. 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. If they painted over the cornea and blocked the entry of light into lower part pupil, the animal had the illusion that they were on a black background, and the frogs became darker. In order to change color scheme coloring of their skin, amphibians need not only to compare the intensity of lighting. They must also estimate the wavelength of the reflected light, i.e. define the background color. Scientists know very little about how this happens.

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, the study of the mechanisms of information processing responsible for chromatophore reactions can lead to very interesting discoveries.

Skin protection

Skin protects against predators

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. Having tasted the toad at least once, the predator remembers the lesson given to it well and no longer dares to touch the representatives of this amphibian species. There is a widespread belief among many people that warts appear on the skin of a person who picks up a toad or a frog. These are prejudices that have no basis, but it must be borne in mind that if the secretions of the skin glands of frogs get on the mucous membranes of the mouth, nose and eyes of a person, they will cause irritation.

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 that of the sea cucumber. sea cucumber, and it is thousands of times more toxic than sodium cyanide.

It would seem, why are amphibians provided with the ability to produce such an effective poison? But in living organisms, everything is arranged expediently. After all, its injection occurs without special devices (teeth, harpoons, thorns, etc.), which other poisonous animals are provided with, so that the poisonous substance enters the blood of the enemy. And the venom of amphibians is released from the skin mainly when the amphibian is squeezed in the teeth of a predator. It is absorbed mainly through the mucous membrane of the mouth of the animal that attacked it.

Frightening coloration
bright coloring amphibians usually indicates that their skin may secrete 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 painted paws.

An interesting fact is connected with the red-bellied American newts, which are brightly colored and completely inedible. The mountain false and non-poisonous red newts that live near them, called "harmless deceivers", are provided with the same bright paint (mimicry). However, false red newts usually outgrow their venomous counterparts considerably and become less like them. Perhaps for this reason, bright colors are specially given to them only for the first 2-3 years. After this period, the grown-up "deceivers" begin to synthesize pigments for a species-typical dark, brown-brown color, and they become more careful.

Experiments were carried out with chickens, which clearly demonstrated the clear effect of warning coloring on them. The chickens were offered brightly colored red-bellied, false red, and false mountain newts as food. As well as dim lungless salamanders. The chickens ate only the “simple-dressed” salamanders. Since the chickens had no experience of meeting amphibians before, then from these unambiguous results of the experiments there should be only one conclusion: “knowledge” about the dangerous coloration is innate. But maybe the parents of the chickens, having learned an unpleasant lesson when they encountered brightly colored poisonous prey, passed this knowledge on to their offspring? Scientists have established that the development, improvement of the instinctive mechanisms of behavior does not occur. There are only successive age stages of its realization, which replace each other at a given moment. Therefore, in a complex set of protective instinctive behavioral reactions, this fear of bright creatures that carry a potential danger was laid down from the very beginning.

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 the insufficiently perfect apparatus for breathing, because the skin serves as an additional organ of the latter. 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 life 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.
Studying at low magnifications the skin of a tree frog, tree frog ( Hyla arborea), we see that when viewed from below, the skin appears black due to the presence in it 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 is produced 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.

CLASS Amphibians (AMRNIVIA)

General characteristics. Amphibians - four-legged vertebrates from the group Anamnia. Their body temperature is variable, depending on the temperature of the external environment. The skin is naked, with a large number of mucous glands. The forebrain has two hemispheres. The nasal cavity communicates with the oral 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. During their study, many outstanding discoveries were made. 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 species of amphibians is far from the same. In larvae and those adults that lead mainly an 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, that is, their body temperature is not constant and depends on the ambient temperature. 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. Plain common frog spawns 1-4 thousand eggs in the spring, and the 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 a 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

Batrachology -(from the Greek Batrachos - frog) studies amphibians, now it is part of herpetology.

Topic planning.

Lesson 1. External structure and lifestyle of the lake frog.

Lesson 2

Lesson 3. Development and reproduction of amphibians.

Lesson 4

Lesson 5

Lesson 6

Basic terms and concepts of the topic.

Amphibians
Hip
legless
tailless
Shin
Sternum
toads
Brush
clavicle
Skin-pulmonary respiration
frogs
Brain
Cerebellum
Forearm
Bud
Medulla
salamanders
Triton
Worms.

Lesson 1

Tasks: on the example of a frog, to acquaint students with the features of the external structure and movement.

Equipment: wet preparation "internal structure of a frog". Table “Type Chordates. Amphibians class.

During the classes

1. Learning new material.

General characteristics of the class

The first terrestrial vertebrates that still retained a connection with aquatic environment. In most species, eggs are devoid of dense shells and can only develop in water. The larvae lead an aquatic lifestyle and only after metamorphosis do they switch to a terrestrial lifestyle. Respiration is pulmonary and cutaneous. The paired limbs of amphibians are arranged in the same way as in all other terrestrial vertebrates - basically, these are five-fingered limbs, which are multi-membered levers (a fish fin is a single-membered lever). A new pulmonary circulation is formed. In adult forms, the lateral line organs usually disappear. In connection with the terrestrial way of life, the middle ear cavity is formed.

Appearance and dimensions.

Habitat

The larva (tadpole) lives in the aquatic environment (fresh water). An adult frog leads an amphibious lifestyle. Our other frogs (grass, moor) after the breeding season live on land - they can be found in the forest, in the meadow.

Traffic

The larva moves with the help of the tail. An adult frog on land moves by jumping, in water it swims, pushing off with hind legs equipped with membranes.

Food

The frog feeds on: airborne insects (flies, mosquitoes), grabbing them with the help of an ejected sticky tongue, ground insects, slugs.

It is able to grasp (with the help of jaws, there are teeth on the upper jaw) even fish fry.

Enemies

Birds (herons, storks); predatory mammals(badger, raccoon dog); predatory fish.

2. Fixing.

What animals are called amphibians?
What living conditions and why limit the spread of amphibians on Earth?
Than by appearance Are amphibians different from fish?
What features of the external structure of amphibians contribute to their life on land, in water?

3. Homework: 45.

Lesson 2

Tasks: on the example of a frog, to acquaint students with the structural features of organ systems and integuments.

Equipment: wet preparations, relief table "Internal structure of a frog".

During the classes

1. Testing knowledge and skills

What environmental factors influence frog activity?
What is the adaptation in the external structure of the frog to life on land?
What are the structural features of a frog associated with life in water?
What role do the front and hind legs of a frog play on land and in water?
Tell us about the life of a frog according to your summer observations.

2. Learning new material.

Covers.

The skin is naked, moist, rich in multicellular glands. The secreted mucus protects the skin from drying out and thereby ensures its participation in gas exchange. The skin has bactericidal properties - it prevents the penetration of pathogenic microorganisms into the body. In toads, toads, some salamanders, the secret secreted by the skin glands contains poisonous substances - none of the animals eat such amphibians. Skin color acts as a camouflage - patronizing coloration. In poisonous species, the color is bright, warning.

Skeleton.

The spinal column is divided into 4 sections:

cervical (1 vertebra)
trunk
sacral
tail

In frogs, the tail vertebrae are fused into one bone - urostyle. The auditory ossicle is formed in the cavity of the middle ear. stapes.

The structure of the limbs:

Nervous system and sense organs.

The transition to a terrestrial way of life was accompanied by a transformation of the central nervous system and sensory organs. The relative size of the amphibian brain compared to fish is small. The forebrain is divided into two hemispheres. Accumulations of nerve cells in the roof of the hemispheres form the primary cerebral fornix - archipallium.

The sense organs provide orientation in the water (larvae and some tailed amphibians have developed lateral line organs) and on land (vision, hearing), smell, touch, taste organs and thermoreceptors.

Respiration and gas exchange.

In general, amphibian milking is characterized by pulmonary and skin respiration. In frogs, these types of breathing are represented in almost equal proportions. Dry-loving gray toads the proportion of pulmonary respiration reaches approximately 705; in newts leading an aquatic lifestyle, cutaneous respiration predominates (70%).

The ratio of pulmonary and skin respiration.

American lungless salamanders and Far Eastern newts have only pulmonary respiration. Some caudate (European Proteus) have external gills.

The lungs of frogs are simple: thin-walled, hollow, cellular sacs that open directly into the laryngeal fissure. Since the neck of the frog, as a department, is absent, there are no airways (trachea). The breathing mechanism is forced, due to the lowering and raising of the bottom of the oropharyngeal cavity. As a result, the frog's skull has a flattened shape.

Digestion.

Fundamental innovations in the structure digestive system, compared to fish, frogs do not. But, salivary glands appear, the secret of which so far only wets the food, without exerting a chemical effect on it. The mechanism of swallowing food is interesting: swallowing is assisted by the eyes moving into the oropharyngeal cavity.

Circulatory system.
The heart is three-chambered, the blood in the heart is mixed (in the right atrium - into the venous, in the left - arterial, in the ventricle - mixed.

The regulation of blood flow is carried out by a special formation - an arterial cone with a spiral valve that directs the most venous blood to the lungs and skin for oxidation, mixed blood to other organs of the body, and arterial blood to the brain. A second circle of blood circulation appeared (lungfish also have a pulmonary circulation).

Selection.

Trunk or mesonephric kidney.

3. Fixing.

What are the similarities in the structure of the skeletons of amphibians and fish?
What features of the skeleton of amphibians distinguish it from the skeleton of fish?
What are the similarities and differences between the digestive systems of amphibians and fish?
Why amphibians can breathe atmospheric air how do they breathe?
How is the circulatory system of amphibians different?

4. Homework . 46, plan your response.

Lesson 3

Tasks: to reveal the features of reproduction and development of amphibians.

Equipment: relief table "Internal structure of a frog".

During the classes

I. Learning new material.

1. Organs of reproduction.

Amphibians are dioecious animals. The reproductive organs of amphibians and fish are similar in structure. The ovaries of females and the testes of males are located in the body cavity. In frogs, fertilization is external. Caviar is deposited in water, sometimes attached to aquatic plants. The shape of the egg clutches is different in different species. Speed embryonic development It strongly depends on the water temperature, so it takes from 5 to 15-30 days before hatching from a tadpole egg. The emerging tadpole is very different from the adult frog; he is dominated by fish features. As the larvae grow and develop, great changes occur: paired limbs appear, gill breathing is replaced by pulmonary breathing, the heart is three-chambered, the second circle of blood circulation. There is a change in appearance. The tail disappears, the shape of the head and body changes, paired limbs develop.

Comparative characteristics of frogs and tadpoles

signs	Tadpole	Frog
body shape	Fish-like. Tail with a capitate membrane. At some stages of development there are no limbs.	The body is shortened. There is no tail. Two pairs of limbs are well developed.
Lifestyle		Terrestrial, semi-aquatic
Movement	Swimming with the tail	On land - jumping with the help of the hind limbs. In water - repulsion by hind limbs
	Algae, protozoa	Insects, molluscs, worms, fish fry
	Gills (first external, then internal). Through the surface of the tail (dermal)	Stucco, leather
Sense organs: Lateral line Hearing (middle ear)	There is no middle ear	Not Has a middle ear
Circulatory system	1 circle of blood circulation. Double chambered heart. Venous blood in the heart	2 circles of blood circulation. Three-chambered heart. The blood in the heart is mixed.

The duration of the larval period depends on the climate: in a warm climate (Ukraine) - 35-40 days, in a cold one (northern Russia) - 60-70 days

In newts, the larvae hatch more formed: they have a more developed tail, large external gills. The very next day they begin to actively hunt for small invertebrates.

The ability of larvae to reproduce sexually is called neoteny.

Some scientists suggest that the amphibian and siren proteas (all tailed amphibians) are neotenic larvae of some salamanders, in which the adult form completely disappeared during evolution.

The larva of a tailed amphibian - ambistoma, is called axolotl. She is able to reproduce.

2. Caring for offspring.

For a number of amphibian species, care for offspring is characteristic, which can manifest itself in a variety of ways.

A) Building nests (or using other shelters for eggs).

Phyllomedusa nest. South American phyllomedusa frogs make nests from plant leaves hanging over water. The larvae live in the nest for some time, and then fall into the water.

The female Ceylon fish snake builds a nest from her own body, wrapping around the eggs laid in the hole. The secretions of the skin glands of the female protects the eggs from drying out.

B) Carrying eggs on the body or in special formations inside.

In the midwife toad, the male winds the bundles of eggs around his hind legs and wears them until the tadpoles hatch.

The male rhinoderm frog hatches eggs in the vocal sac. Hatched tadpoles fuse with the walls of the bag: contact with circulatory system adult- this ensures the supply of nutrients and oxygen to the blood of the tadpole, and the decay products are carried away by the blood of the male.

In the Surinamese pipa, eggs (eggs) develop in leathery cells on the back. Small frogs that have completed metamorphosis emerge from the eggs.

Such care for offspring is caused primarily by a lack of oxygen in the water, as well as a large number of predators in tropical waters.

B) viviparity.

Known for caudates (alpine salamander), some legless and anurans (some desert toads).

II. Testing knowledge and skills.

Oral survey.
Students work with cards.

III. Homework:§ 47, answer the questions of the textbook.

Lesson 4

Tasks: prove the origin of amphibians from ancient lobe-finned fish.

Equipment: wet preparations, tables.

During the classes

I. Testing knowledge and skills.

1. Conversation with students on the following questions:

When and where do amphibians breed?
What are the similarities in the reproduction of amphibians and fish?
What proves this similarity?
What is the main difference between fish and amphibians?

2. Work with cards.

A close connection with water, similarities with fish in the early stages of development indicate the origin of amphibians from ancient fish. It remains to be clarified from which particular group of fish amphibians originate and what force drove them out of the aquatic environment and forced them to switch to terrestrial existence. Modern lungfish were considered amphibious, and then they began to see them as a link between amphibians and real fish.

The appearance of the oldest amphibians dates back to the end of the Devonian period, and the heyday to the Carboniferous.

Initially, amphibians were represented by small forms. The oldest fossil amphibians carboniferous period on general form bodies resemble our newts, but differ from all modern amphibians strong development skin skeleton, especially on the head. Therefore, they were allocated to a special subclass stegocephalians.

The structure of the skull is the most characteristic feature of the stegocephalians. It consists of numerous bones, tightly closing with each other and leaving a hole only for the eyes, nostrils, and there is another unpaired hole on the crown of the head. In most stegocephalians, the ventral side of the body was covered with a shell of scales sitting in rows. The axial skeleton is poorly developed: the notochord was preserved and the vertebrae consisted of separate elements that were not yet soldered into one continuous whole.

According to the theory of Academician I.I. Schmalhausen, amphibians, and therefore all terrestrial vertebrates, descended from ancient freshwater lobe-finned fish. An intermediate form between fish and amphibians is called ichthyostegi.

III. Anchoring

Choose the correct answer option I

The teacher completes the students' answers.

IV. Homework:§ 47 to the end, answer questions.

Lesson 5

Tasks: To introduce students to the diversity of amphibians and their importance.

Equipment: tables.

During the classes

I. Testing knowledge and skills.

Students work with cards.
Conversation with students about the textbook.
Oral responses.

II. Learning new material.

Ancient amphibians were more confined to water bodies than their modern descendants. In the aquatic environment, they were kept by a heavy bone skull and a weak spine. As a result, the group of stegocephalians, which gave rise to both the later amphibians and the most ancient reptiles, ceased to exist, and the further development of the class went in the direction of unloading the bone skull, eliminating bone formations on the skin and ossifying the spine. At present, the process of historical development of amphibians has led to the formation of three sharply isolated groups - the orders of caudate and tailless amphibians already known to us and a very peculiar order of legless, or caecilians, in which there are about 50 species confined to humid tropical countries of both hemispheres. This is a specialized group, whose representatives "went underground": they live in the soil, feeding on various living creatures there, and in appearance resemble earthworms.

In the modern fauna, the most prosperous group is the tailless amphibians (about 2100 species). Within this group, further development went in different directions: some forms remained closely associated with the aquatic environment (green frogs), others turned out to be more adapted to terrestrial existence (brown frogs and especially toads), others switched to life on trees (tree frogs), dispersing thus in the living communities (biocenoses) of our modern nature.

Feeding on various small living creatures, amphibians exterminate a significant number of insects and their larvae. Therefore, frogs and toads can be included in the category of crop protectors and friends of gardeners and gardeners.

III. Homework: § 48, repeat §§ 45-47.

Offset. class amphibians

OPTION I

Choose the correct answer

1. Amphibians - the first vertebrates:

a) landed and became completely independent of water;

b) landed, but did not break the connection with water;

c) landed, and only a few of them cannot live without water;

d) become dioecious.

2. amphibians with skin:

a) they can drink water;

b) cannot drink water;

c) some can drink water, others cannot;

d) Distinguish between light and darkness.

3. During pulmonary breathing, inhalation in amphibians is carried out due to:

a) lowering and raising the bottom of the oral cavity;

b) change in the volume of the body cavity;

c) swallowing movements

d) diffusion.

4. Real ribs have amphibians:

a) only tailless;

b) only caudate;

c) both tailless and tailed;

d) only in the larval state.

5. Blood flows through the body of adult amphibians:

a) one circle of blood circulation;

b) in two circles of blood circulation;

c) in the majority in two circles of blood circulation;

d) in three circles of blood circulation.

6. In cervical region the spine of amphibians is available:

a) three cervical vertebrae;

b) two cervical vertebrae;

c) one cervical vertebra;

d) four cervical vertebrae.

7. The forebrain in amphibians compared to the forebrain of fish:

a) larger, with complete division into two hemispheres;

b) larger, but without division into hemispheres;

c) has not changed;

d) smaller.

8. The hearing organ of amphibians consists of:

a) inner ear

b) inner and middle ear;

c) inner, middle and outer ear;

d) outer ear.

9. Urogenital organs in amphibians open:

a) in the cloaca;

b) independent holes;

c) in anurans - into the cloaca, in caudates - with independent external openings;

d) one independent outer hole,

10. Heart in tadpoles:

a) three-chamber;

b) two-chamber;

c) two-chamber or three-chamber;

d) four-chamber.

OPTION II

Choose the correct answer

1. Skin in amphibians:

a) all naked, mucous, devoid of any keratinized cells;

b) everyone has a keratinized layer of cells;

c) in the majority it is naked, mucous, in a few it has a keratinized layer of cells;

d) dry, devoid of any glands.

2. Amphibians breathe with:

a) skin only

b) lungs and skin;

c) only lungs;

d) only gills.

3. Heart in adult amphibians:

a) three-chamber, consisting of two atria and a ventricle;

b) three-chamber, consisting of an atrium and two ventricles;

c) two-chamber, consisting of an atrium and a ventricle;

d) four-chamber, consisting of two atria and two ventricles.

4. Cerebellum in amphibians:

a) everyone is very small;

b) very small, in some species of caudates it is practically absent;

c) larger than fish;

d) the same as in fish.

5. Vision in amphibians compared to vision in fish:

a) less farsighted;

b) more farsighted;

c) remained unchanged;

d) has almost lost its meaning.

6. Lateral line organs in adult amphibians:

a) are absent;

b) are present in most species;

c) are present in those species that constantly or spend most of their lives in water;

d) are present in those species that spend most of their lives on land.

7. Adult amphibians eat:

a) filamentous algae;

b) various aquatic plants;

c) plants, invertebrates and rarely vertebrates;

d) invertebrates, rarely vertebrates.

8. Teeth in amphibians:

a) are present in many species;

b) are available only in caudates;

c) available only in anurans;

d) absent in most species.

9. Fertilization in amphibians:

a) everyone has an internal;

b) all external;

c) in some species it is internal, in others it is external;

d) most internal.

10. The life of amphibians is associated with water bodies:

a) salty

b) fresh;

c) both salty and fresh.

11. Amphibians originated:

a) from coelacanths considered extinct;

b) extinct freshwater lobe-finned fish;

c) lungfish

Write down the numbers of the correct judgments.

Amphibians are vertebrates,
reproduction of which is associated with water.
Amphibians have a middle ear, separated from the external environment by the tympanic membrane.
The skin of toads has keratinized cells.
Among amphibians, the largest animal is the Nile crocodile.
Toads live on land and breed in water.
In the skeleton of the belt of the forelimbs of amphibians there are crow bones.
The eyes of amphibians have movable eyelids.
Leather pond frog always wet - it does not have time to dry while the animal is on land for some time.
All amphibians have swimming membranes between the toes of their hind legs.
Amphibians, like fish, lack salivary glands.
The forebrain in amphibians is better developed than in fish.
The heart of tailless amphibians is three-chambered, while that of caudates is two-chambered.
Mixed blood enters the organs of the body in amphibians through the blood vessels.
Frogs are dioecious animals, newts are hermaphrodites.
Fertilization in most amphibians is internal - females lay fertilized eggs.
Development in most amphibians occurs with transformations according to the scheme: egg-larva different ages- an adult animal.
Some of the amphibians are twilight and night image life and are of great help to humans in reducing the number of slugs and other plant pests.

Type chordates. Class Reptiles or Reptiles.

herpetology- (from the Greek. Herpeton - reptiles) - studies reptiles and amphibians.

Theme Planning

Lesson 1 (Annex 6)

Lesson 2. Features internal structure. (Annex 7)

Lesson 3 (

What is the skin of amphibians. General covers of amphibians. Learning new material

Specific features of the skin

Skin respiration

Helps skin breathe

Lesson 1

Lesson 2

Lesson 3

Lesson 4

Lesson 5

Offset. class amphibians

Type chordates. Class Reptiles or Reptiles.

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