It seems to almost all of us that we can, without any particular problems, define any concept from the program of a general education school. For example, amphibians are frogs, turtles, crocodiles and similar representatives of the flora. Yes, it's true. We are able to name some representatives, but what about the description of their characteristic features or way of life? For some reason, they are allocated in a special class? What is the reason? And what is the pattern? Here with it, you see, more difficult.

What will they surprise us with?

It is likely that the respiratory system of amphibians is different from the internal structure of, say, mammals or reptiles. But what? Are there any similarities between us and them? We will try to answer all these questions in this article. However, it is worth paying attention to the fact that in the process of studying the material, the reader will not only learn what the amphibians are similar to each other (turtles and crocodiles, by the way, do not apply to them), but also get acquainted with the most interesting facts related to the data. animals. We vouch for something you had no idea. Why? The thing is that a paragraph of a school textbook does not always provide the whole necessary range of knowledge.

General class information

The class Amphibians (or Amphibians) represents primitive ancestors which more than 360 million years ago changed their habitat and emerged from water on land. Translated from the ancient Greek language, the name translates as "living a double life."

It should be noted that amphibians are cold-blooded creatures with non-constant body temperature, depending on external living conditions.

In the warm season, they are usually active, but when it gets cold, they hibernate. Amphibians appear (frogs, tritons, salamanders) in the water, but most of their existence is carried out on land. This feature can be called almost the main in the life of this species of living beings.

Amphibian species

In general, this class of animals includes more than 3,000 species of amphibians, represented by three groups:

• tailed (salamander);
• tailless (frogs);
• legless (worms).

Amphibians appeared in places with a temperate and hot climate. However, to this day they live there.

Basically, they are all small and have a length of not more than one meter. The exception is (the main signs of amphibians are blurred in her), living in Japan and reaching a length of one and a half meters.

Amphibians spend their lives alone. Scientists have determined that this did not happen as a result of evolution. The first amphibians led exactly the same way of life.

Among other things, they are perfectly masked, changing their color. By the way, not everyone knows that the poison released by special skin glands also serves as protection against predators. Perhaps only reptiles, arthropods and amphibians have this feature. Mammals with such a set of characteristic features are not found in nature. In fact, it is difficult to even imagine, for example, a cat familiar to all of us could adjust the temperature of his own body depending on changes in the environment or excrete poison, defending himself from the dog attacking it.

Peculiarities of the skin

All amphibious animals have a smooth thin skin that is rich in skin glands, which secrete mucus that is necessary for gas exchange.

Excreted mucus also protects the skin from drying out and may contain toxic or signal substances. Multilayer epidermis is abundantly supplied with a network of capillaries. Most poisonous individuals can take on a bright color, serving as a protective and warning device from predators.

Some amphibians of the tailless group on the upper layer of the epidermis are found to have keratinized formations. This is especially developed in toads, in which more than half of the skin surface is covered with the stratum corneum. It is important to note that weak keratinization of the cover does not prevent the penetration of water through the skin. Thus, the breathing of amphibians is arranged, which are able to breathe under water only with the skin.

In terrestrial species, keratinous skin may form claws on limbs. In tailless amphibians, the entire subcutaneous space is occupied by lymphatic lacunae, cavities where water is accumulated. And only in a few places the connective tissue of the skin connects with the muscles of the amphibian.

Amphibian lifestyle

Amphibians, photos of which can be found in all textbooks on zoology, without exception, undergo several stages of development: those born in water and having similarities with fish as a result of transformation acquire lung breathing and ability to live on land.

This development does not occur in other vertebrates, but is common in primitive invertebrates.

They occupy an intermediate position between aquatic and terrestrial vertebrates. Amphibians live (fish in this regard are more adapted representatives of the fauna) in all parts of the world where there is freshwater, with the exception of cold countries. Most of them spend half their life in water. In others, adults live on the ground, but in places with high humidity and near water.

During a drought, amphibians (birds could envy such features) fall into anabiosis, buried in mud, and during cold weather in areas with a temperate climate are prone to hibernation.

The most favorable habitats are tropical countries with wet forests. Least of all, amphibians prefer dry areas of nature (Central Asia, Australia, etc.).

These are aquatic and terrestrial inhabitants, who usually prefer nightlife. The day is spent in hiding or half asleep. Tailed species move along the ground like reptiles, and tailless ones - with short jumps.

Amphibians are animals that, as a rule, are capable of climbing trees. Unlike reptiles, adult amphibian males are very vocal, they are silent in their youth.

Food in most cases depends on the age and stage of development. Larvae eat plant and animal microorganisms. As they grow older, there is a need for live food. These are already real predators, feeding on worms, insects and small vertebrates. During the heat, their appetite increases. The inhabitants of the tropics are much more voracious than their relatives from countries with a temperate climate.

At the beginning of life, amphibians, whose photos adorn the atlases, vividly showing the evolution of human development, develop rapidly, but over time their growth slows down considerably. The growth of frogs continues up to 10 years, although they reach maturity by the age of 4-5. In other species, growth stops only by 30 years.

In general, it should be noted that amphibians are very hardy animals that can endure hunger as well as reptiles. For example, a toad planted in a damp place may be without food for up to two years. The respiratory system of amphibians at the same time continues to function fully.

Amphibians also have the ability to regenerate lost parts of the body. However, in highly organized amphibians such properties are less pronounced or are completely absent.

Like reptiles, wounds also heal quickly in amphibians. The tailed species are distinguished by their particular vitality. If a salamander or a triton freeze in water, they become numb and brittle. As soon as the ice melts, the animals return to life again. Once the triton is taken out of the water, it instantly shrinks and shows no signs of life. Put it back - and the newt comes to life immediately.

The shape of the body and the structure of the skeleton are similar to fish. The brain consists of two hemispheres, the cerebellum and the midbrain and has a simple structure. The spinal cord is more developed than the head. Amphibian teeth serve only to capture and hold prey, but are not at all adapted for chewing. Of great importance for the life of amphibians are the respiratory and circulatory systems. They, like reptiles, have cold blood.

By appearance  and amphibians (tortoises, we recall, do not belong to them, although they sometimes lead a similar lifestyle) are divided into three groups: tailless, tailed, and legless. Representatives of tailless are frogs, which are distributed throughout the world where there is moisture and enough food. Frogs love to sit on the beach and bask in the sun. At the slightest danger, they rush into the water and bury themselves in silt.

Representatives of such a huge group of animals as the class Amphibians swim well. As the cold approaches, the amphibians hibernate. Spawning occurs in the warm season. The development of eggs and tadpoles is fast. Their main food is plant and animal food.

They look like lizards. Live in ponds or near water. They are nocturnal, and during the day they hide in shelters. Unlike lizards, on land they are slow and sluggish, but very agile in water. They feed on small fish, mollusks, insects and other small animals. This species includes salamanders, tritons, proteas, skins, etc.

To the order of legless amphibians are worms that have an external resemblance to snakes, however, in development and internal structure, they are close to salamanders and proteins. Worms live in tropical countries (except Madagascar and Australia). They live underground, laying passages. They lead the same way of life as the earthworms that make up their diet. Some worms bring viviparous offspring. Others lay their eggs in the soil next to the water or in the water.

The use of amphibians

Amphibians belong to the first and most primitive occupying a special place in the evolution of terrestrial vertebrates, which is the least studied.

For example, the role of birds and mammals in human life has long been known. In this respect, amphibians are very far behind. However, they are also of great importance in human activities. As you know, in many countries, frog legs are delicacies and highly valued. For these purposes, about one hundred million frogs are harvested annually in Europe and North America. This indicates that amphibians are also of economic importance.

Adults feed on animal food. Eating harmful insects in gardens, kitchen gardens and fields, they benefit the person. Among insects, mollusks or worms there are also carriers of various dangerous diseases.

Amphibians that feed on aquatic microorganisms are considered less useful. The exception is tritons. And although the basis of their food includes aquatic organisms, they also eat mosquito larvae (including malarial), which breed in water bodies with warm and stagnant water.

The use of amphibians largely depends on their number, seasonal, fodder and other features. All of these factors affect the nutrition of amphibians. For example, living in reservoirs, it is more useful than its relatives, living in other places.

Unlike birds, amphibians exterminate a greater number of insects with scare and protective functions that birds do not eat. Also land species of amphibians feed mainly at night, when many insectivorous birds sleep.

The full value of amphibians in human life can be assessed only with sufficient study of these animals. At present, the biology of amphibians has extremely superficial knowledge.

Amphibians as an important part of the food chain

In some fur animals, most amphibians are the main feed. For example, the survival rate of a raccoon dog in different habitats directly depends on the number of amphibians in these areas.

Mink, otter, badger and black polecat eater willingly eat amphibians. Therefore, the number of these animals is significant for hunting grounds. Amphibians are included in the diet and other predators. Especially when there is not enough main food - small rodents.

In addition, valuable commercial fish in the winter period in reservoirs and rivers feed on frogs. Most often, their prey becomes a grass frog, which, unlike a green frog, does not bury itself for wintering in silt. In summer, she eats ground invertebrates, and in winter she goes for wintering into the lake. Thus, the amphibian becomes an intermediate link and replenishes the food base for fish.

Amphibians and science

Due to their structure and survivability, amphibians began to be used as laboratory animals. It is on the frog that the greatest number of experiments are conducted, ranging from biology lessons at school and ending with major medical research scientists. For these purposes, more than tens of thousands of frogs are used annually as biological material in laboratories. It is possible that this may lead to the complete destruction of animals. By the way, in England, catching frogs is prohibited, and they are now under protection.

It is difficult to list all the scientific discoveries related to the experiments and physiological experiments on frogs. Recently, their use has been found in laboratory and clinical practice for the early diagnosis of pregnancy. The introduction of the urine of pregnant women to males of frogs and toads causes in them a rapid process of spermatogenesis. In this respect, the green toad stands out in particular.

The most unusual amphibious planets

Among the poorly studied species of these animals there are many rare and unusual specimens.

For example, ghost frogs (genus Heleophryne) are in fact the only family of tailless amphibians with only six species, one of which is found only in a cemetery. Apparently, this is where the rather unusual name of the species came from. They live mainly in the north-east of South Africa near forest streams. Sizes up to 5 cm and camouflage coloring. They are nocturnal, and at night they hide under stones. True, today two species are almost exterminated.

Proteus (Proteus anguinus) is a tailed species of the class Amphibians living in underground lakes. It reaches lengths up to 30 cm. All individuals are blind and have transparent skin. Proteus hunts due to electrical sensitivity of the skin and smell. Can live without food for up to 10 years.

The next representative, the frog Zooglossus Gardner (Sooglossus gardineri), belongs to one of the unusual tailless species of the Amphibian family. Is under threat of destruction. Has a length of not more than 11 mm.

Darwin's frog is a fairly small tailless amphibian species that lives in cold mountain lakes. The body length is about 3 cm. Males carry their offspring in the throat sac.

• Even not all avid travelers are aware that in the state of Peru there are many cafes where special frog cocktails are prepared. It is believed that such drinks relieve many diseases, treat asthma and bronchitis, help restore potency. One of the cooking methods is to chop a living frog in a blender with the addition of bean soup, honey, aloe juice and poppy root. Are you ready to decide and try this dish?
• Unusual amphibians live in South America. Paradoxical frogs as they grow older decrease in size. The usual length of an adult individual reaches only 6 cm. However, their tadpoles grow to 25 cm. A strange feature.
• During experiments on laboratory frogs, Australian researchers made a random discovery. They found that these animals are capable of removing foreign bodies from their bodies through the bladder. Experienced and very eminent scientists implanted animal transmitters, which after some time moved into their bladders. Thus, it turned out that when foreign bodies enter the body of amphibians, they gradually become overgrown with soft tissues and are drawn into the bladder. This discovery actually made a revolution in science.
• Few ordinary people know that the reason for the frequent blinking of frogs during a meal is pushing food into the throat. Animals are not able to chew food and push its tongue into the esophagus. Blinking, eyes retract into the skull with special muscles and help push food through.
• A very interesting specimen is the African frog Trichobatrachus robustus, which has an amazing adaptation to protect against enemies. At the time of the threat of its paws pierce the bones of the subcutaneous, forming a kind of "claws". After the danger has passed, the claws are retracted, and the damaged tissue regenerates. Agree, not every representative of the modern fauna can boast of having such a useful and unique feature.

Repeat the general characteristics and classification of the Chord type.

To study aromorphosis class Amphibians. Write in a notebook.

To study the structure of amphibians. Perform a summary in a notebook.

Consider wet preparations of different types of amphibians.

Examine the external and internal structure  amphibians on the example of the frog (opening the frog).

In the album, make 6 drawings labeled V (red tick) in the printed training manual. Their (printed manuals) should be sought in the laboratory department of biology and ecology. In this electronic training manual drawings are placed at the end of the material.

In the notebook draw and fill in table 1 .:

Table 1. Comparative characteristics of a frog and a tadpole.

In the notebook draw and fill in table 2.:

Table 2. Amphibian Diversity

Know the answers to test questions   Topics:

General characteristics of the type of Chord. Classification of Chord type.

Features of the organization of amphibians.

Systematic position, lifestyle, body structure, reproduction, meaning in nature and for humans Frog.

General characteristics of amphibians

In modern animal systematics, Amphibians (Amphibia), or else they are called Amphibians, is a class in the Chordata type of the Vertebrata subtype.

Amphibian Aromorphoses

Basic Aromorphosis  (Aromorphoses are major evolutionary changes leading to a general complication of the structure and organization of the body) The following are amphibians:

1. the formation of five-limb;

   development of sacciform lung;

   three-chambered heart and the emergence of the second circle of blood circulation;

   progressive development of the nervous system;

   muscle differentiation;

   the formation of the middle ear.

Amphibians- the first terrestrial vertebrates, which retained a connection with the aquatic environment. They occupy an intermediate position between these terrestrial and aquatic vertebrates: reproduction and development occur in the aquatic environment, and adult individuals live on land.

Amphibians are descended from the ancient Devonian cross-finned fishes (350 - 345 mln BP). Modern amphibious detachments appeared at the end of the Jurassic - at the beginning of the Cretaceous (135-130 mln BP) of the Mesozoic era and have survived to this day.

Modern amphibians include three orders: legless(about 200 species), tailed(about 400 species) and tailless(about 4 thousand species). They are widely distributed in various natural zones, mainly inhabiting wet places and shores of water bodies. Cold-blooded animals are active in the morning and evening when the air humidity and temperature are quite high.

Amphibian structure

The structure of amphibians should be considered as an example. Grass frogs– Rana temporaria  (Chord type, Vertebrate subtype, Amphibian class, Tailless order). For work, you can use both brown frogs (grass frog species) and green frogs (L. pond species, L. lake species). Frogs live almost throughout the entire territory of our country, except for the Far North, Siberia and high-mountainous regions. They live in damp places: in swamps, wet forests, in meadows, along the banks of freshwater bodies of water, or in water. The behavior of frogs is largely determined by humidity. In dry weather, brown land frogs hide from the sun, but after its setting or in wet rainy weather, the time of their hunting begins.

Green frogs live in the water or near the water, so they hunt during the day. The frogs feed on various insects, mainly beetles and dipterans, but they also eat spiders, terrestrial and aquatic gastropods, and sometimes fish fry. The frogs lurk their prey, sitting motionless in a secluded place.

When hunting, the main role is played by sight. Having noticed any insect or other small animal, the frog throws out of its mouth a wide sticky tongue, to which the prey sticks. Frogs grab only moving prey.

Frogs are active only in the warm season. With the onset of autumn, they go to the winter. Winter is spent at the bottom of reservoirs or hiding in pits, burrows of rodents, under heaps of stones.

Having spent the winter in a state of stupor, the frogs wake up with the first rays of the spring sun and start reproduction. During this period, the males cry loudly. The amplification of sounds is facilitated by special bags - resonators, which, when croaking, swell on the sides of the male's head. When breeding animals are divided in pairs. Genital cells through the tubular channels enter the cloaca, and from there they are thrown out.

Amphibian females lay eggs in the water, similar to fish eggs. Males produce sperm on it containing sperm. After some time, the shell of each egg swells and turns into a gelatinous transparent layer, inside which you can see an egg. The upper half of it is dark and the lower half is light: the dark part of the egg uses the sun's rays better and heats up more. Clumps of caviar in many species of frogs float to the surface where the water is warmer. Low temperature retards development. If the weather is warm, the egg repeatedly divides and turns into a multicellular embryo. After one or two weeks, the larva of the frog hatches from the egg tadpole.Outwardly, it resembles a small fish with an egg-shaped body and a large tail. The tadpole first breathes with external gills (in the form of small tufts on the sides of the head). Soon they are replaced by internal gills.

The tadpole has only one circulation and a two-chamber heart, and there are visible sideline organs on the skin. Thus, the larva of the frog (and other amphibians) has some structural features of the fish.

The first days the tadpole lives at the expense of the nutrient reserves of the egg. Then his mouth is cut through, equipped with horny jaws. Tadpoles begin to feed on algae, protozoa and other aquatic organisms.

General characteristics of amphibians

Further changes to tadpoles are the sooner the hotter the weather. First, they have hind legs, then front ones. The lungs develop. Tadpoles begin to rise to the surface of the water and swallow air. The tail is gradually shortened, the tadpole becomes a young frog and goes to the shore. From the moment of laying the roe to the end of the tadpole turning into a frog, it takes about 2-3 months. Frogs, like adult frogs, eat animal food. They can multiply from the third year of life.

So, the body of a frog consists of the head, body and paired limbs. The head is wide, flattened, with a large oral slit and bulging eyes, behind which there are two rounded eardrums that cover the outside of the middle ear cavity (Fig. 1). The pair of external nostrils is closed by valves and connected to the internal nostrils - the joans. The neck is almost not expressed. The body is flattened and movably connected to the head.

Fig. 1. The head of a frog.

1 - mouth; 2 - external nasal opening; 3 - upper eyelid; 4 - lower eyelid; 5 - eardrum; 6 - external resonators; 7 - language; 8 - choans; 9 - holes of Eustachian tubes; 10 - laryngeal fissure; 11 - vomer teeth; 12 - the eye.

General characteristics of amphibians

Veils.Skin bare, without scales. Consists of a multi-layered epidermis and the skin itself. The epidermis contains multicellular glands that secrete mucus, which has bactericidal properties and facilitates gas exchange (skin respiration).

Skeletonconsists of the axial skeleton of the trunk (spine), the skeleton of the head (skull) and the skeleton of paired limbs (Fig. 2).

Fig. 2. Skeleton of a frog.

1 - the skull; 2 - scapula; 3 - the spine; 4 - pelvic bones; 5 - tail bone; 6 - thigh; 7 - bones of a shin (have grown together in one); 8 - foot; 9 - shoulder; 10 - forearm; 11 - brush; 12 - sternum; 13 - the clavicle.

General characteristics of amphibians

Spinein connection with the movement of jumps it is strongly shortened, the vertebrae are firmly articulated with each other. Consists of four departments: cervical- includes one vertebra movably attached to the occipital region of the skull; trunk- includes seven vertebrae, ribs reduced or absent; sacral- includes one vertebra bearing the long transverse processes to which the iliac bones of the pelvis are attached; tail- vertebrae grow together, forming a long bone - urostyle.

Skullwide and flat, a significant portion formed by cartilage. The large openings of the orbits are located on the top, not from the sides, like in fish. Connects to the spine with two condyles formed by the occipital bones.

Limb skeletonincludes limb girdles and skeleton of free limbs. Shoulder girdlerepresented by paired bones - shoulder blades, collarbone, crow bones (coracoids) and unpaired bone of the sternum. There is no chest. The skeleton of the forelimb consists of the shoulder (humerus), the forearm (accreted radial and ulna bones) and the wrist (the wrist, metacarpus and phalanxes of the fingers). Pelvic girdlerepresented by paired iliac, sciatic and pubic bones, fused together in the pelvis. It is attached to the sacral vertebra through the ilium. The skeleton of the hind limb consists of the femur (femur), tibia (accreted large and small shin bones), and the feet (tarsal bones, metatarsus and phalanxes of the fingers). Before the first finger of the hind limb there is a rudiment of the additional finger. The elongated fingers are connected by a swimming membrane.

The internal structure of amphibians is presented in Figure 3.

Muscular systemcomplicated and specializes in connection with the movement on a solid substrate (landfall). The muscles of the head raise and lower the lower jaw. The muscles of the floor of the mouth are involved in the process of pulmonary respiration. The body muscles are segmented and represented by muscle bands separated by connective tissue. Strongly developed muscles of the limbs (especially the rear).

Nervous system.The brain consists of five sections: frontthe brain is larger than that of fish; the hemispheres of the brain are completely separated; the bottom of the lateral ventricles, the sides and the roof contain nerve cells, i.e. a real cerebral vault is formed - archipallium,old bark; intermediatethe brain is well developed, collects information from all sense organs, regulates the work of the endocrine glands; averagethe brain is relatively small in size, contains visual shares; cerebellumpoorly developed due to monotonous, uncomplicated movements; oblongthe brain is the center of regulation of the respiratory, circulatory and digestive systems. Ten pairs of cranial nerves are moving away from the brain.

General characteristics of amphibians

Fig. 3. Anatomy of the female frog.

1 - the esophagus; 2 - the stomach; 3, 3 ", C 2 - liver lobes; 4 - pancreas; 5 - small intestine; 6 - rectum; 7 - cloaca; 8 - heart ventricle; 9 - left atrium; 10 - right atrium; 11 - carotid artery ( right); 12 — aortic root (left); 13 — pulmonary artery (left); 14 — inferior vena cava (posterior); 15 — abdominal vein; 16 — lungs; 17 — left kidney; 18 — right ovary; 19 — left. ovary; 20 - mouth (funnel) of the left oviduct; 21 - bladder; 22 - gallbladder; 23 - spleen.

General characteristics of amphibians

Spinal cord  enclosed in the spinal canal of the spine. Spinal nerves form the brachial and lumbar plexus. The sympathetic nervous system is well developed, represented by two nerve trunks located on the sides of the spine.

The behavior of amphibians is simple and based on unconditioned reflexes.

Sense organs. Organs of tastelocated in the oral cavity and developed very weakly. There are only bitter and salty. Organs of smellrepresented by olfactory bags with a folded surface lined by sensitive epithelium. Olfactory bags are connected with the external environment - paired external nostrils, with the oropharyngeal cavity - internal nostrils (choans). Differentiation of the nasal cavity into the olfactory and respiratory parts begins, the nasolacrimal canal and glands appear (wetting the mucous membrane of the olfactory sacs). The respiratory part of the olfactory sac does not have folds and is lined with simple epithelium. The olfactory organ functions only in air, and in water, the external nostrils are closed by valves. In the area of ​​Choan, there is a Jacobson (Vomeronosal) organ for obtaining olfactory information about food in the oral cavity. Organs of vision(eyes) have a structure characteristic of terrestrial animals. Binocular vision. The cornea becomes convex (flattens out in water), the lens takes the form of a biconvex lens, which increases hyperopia. Circular muscles of the pupil and lens appear. Accommodation of vision is carried out by moving the lens with the help of contraction of the ciliary muscle. Adults have eyelids (upper and lower), a blinking membrane (third eyelid) in the front corner of the eye, protecting it from drying out and pollution. There is a lacrimal gland, the secret of which washes the eyeball. Organ of hearing and balancerepresented by the middle, inner ear with three semicircular canals (organ of balance). The organ of hearing is adapted to the perception of sound stimuli in the air environment. The external auditory orifices are located on the head behind the eyes and tightened by a rounded eardrum that perceives sound vibrations. Oscillations of the membrane are transmitted to the auditory bone - stapes, - located in the middle ear cavity. The stirrup rests against the oval window leading to the cavity of the inner ear, transmitting to it vibrations of the eardrum. The lower part of the middle ear cavity is opened in the oropharynx using an auditory (Eustachian) tube to equalize pressure on both sides of the eardrum. Tactile organs- skin receptors. The lateral line is characteristic of the larvae of all amphibians. The sensitive cells of this organ are not located in the recessed channel, but lie superficially in the skin.

Digestive system.All amphibians are active predators reacting to mobile prey (invertebrates, fish fry). The oral opening leads to the vast oropharyngeal cavity, which is devoid of gill slits (with the exception of tadpole larvae). The roof cavity is

General characteristics of amphibians

base of the skull - primary hard palate. The teeth are not differentiated, are located on the upper jaw and serve to keep the prey. The tongue is bifid, attached by the front end to the lower jaw and easily thrown out after the prey. In the oral cavity open ducts of the salivary glands. Swallowing prey helps the eye, retracting into the oral cavity. Next is a short esophagus, stomach, intestine, consisting of the duodenum (where the ducts of the liver and pancreas flow), the small intestine and the rectum, ending with the expansion - the cloaca. The ducts of the gonads, the ureters and the bladder (outgrowth of the wall of the cloaca) flow into the cloaca.

Respiratory system.In the adult state, breathing occurs with the help of paired lungs and skin. Light - paired bags with thin cellular walls, penetrated by blood capillaries, where gas exchange occurs. The airways are short, represented by the nasal and oropharyngeal cavities, larynx. In the larynx of the males there are vocal cords (capable of making sounds). Breathing is provided by the movements of the bottom of the oropharyngeal cavity. When lowering the bottom, air is sucked into the oropharyngeal cavity through the nostrils. When raising the bottom of the cavity and closing the nostrils with valves, the air is pushed into the lungs. The respiratory surface of the lungs is small and correlates with the surface area of ​​the skin as 2: 3. Additional gas exchange occurs through moist skin. Skin respiration is carried out both in water and on land. Of particular importance it has a long stay in the water (during hibernation, in case of danger). In the larval state, respiration occurs through the gills.

Circulatory systemclosed, consists of small (pulmonary) and big circles of blood circulation. The appearance of the second round is associated with the appearance of pulmonary respiration. The heart is three-chambered, consists of two atria and one ventricle, which has folds (trabeculae) on the inner surface, preventing the complete mixing of arterial and venous blood. Both atria open into the ventricle with one common opening. From the ventricle out one vessel - arterial conewith a spiral valve at the base that provides blood distribution. Three pairs of arteries extend from the arterial cone: skin and pulmonary arteriescarry venous blood to the skin and lungs; right and left aortic archescarry mixed blood, merging, form spinal aorta,from which the arteries move to all parts and organs of the body. Carotid arteriescarry arterial blood to the head.

From the back of the body, blood is collected in the unpaired posterior vena cava, passing through the portal system of the liver and kidneys, flows into the venous sinus and the right atrium. From the front of the body, venous blood is collected in the right and left anterior hollow veins, in the venous sinus and right atrium.

Small (pulmonary) circulationbegins with the skin and pulmonary arteries that carry venous blood to the respiratory organs, where

General characteristics of amphibians

gas exchange From the lungs, oxygen-rich blood flows through the paired pulmonary veins into the left atrium.

Great Circle of Blood Circulationbegins with aortic arches and carotid arteries that branch out in organs and tissues. Venous blood through the paired anterior hollow vein and unpaired posterior vein enters the right atrium. In the front of the hollow veins and skin of the corresponding side of the veins that carry arterial blood.

Excretory systemrepresented by paired oblong trunk (mesonephros, primary) kidneys, lying in the body cavity on the sides of the spine; ureters and bladder. In the trunk of the kidney does not reverse the absorption of water, so the bladder is a reservoir of water in which it is reabsorbed. When the bladder is filled, urine is thrown out through the opening of the cloaca. Additional organs of excretion are the skin and lungs. The main end product of metabolism is urea. A large loss of water by the body through the organs of excretion and the surface of the skin does not allow the frog to leave wet places for a long time.

The reproductive system.Separated. The sex glands are paired. In males, the testes do not have independent excretory pathways. The seminiferous tubules pass through the anterior part of the kidney and flow into the ureters, which simultaneously serve as the vas deferens. Before flowing into the cloaca, an expansion is formed - the seminal vesicle in which the seed is temporarily reserved. Above the testes are fatty bodies, which serve to nourish the testes and the spermatozoa developing in them. The amount of fat bodies varies by seasons. In the fall they are great; in the spring, during intensive spermatogenesis, their substance is vigorously consumed, and the size of fat bodies is sharply reduced. There are no copulatory organs. Female ovaries in spring are enlarged and fill the entire abdominal cavity. They contain mature ova (eggs). Through the rupture of the thin wall of the ovary, the eggs fall out into the body cavity and, through the funnel of the oviduct, enter the long, convoluted oviduct, which opens into the cloaca. Fertilization is external, occurs in the water. Amphibians are anamnias, i.e. vertebrate animals whose embryos do not have special germinal membranes, therefore the development of the embryo occurs in the aquatic environment.

Development(indirect) occurs with metamorphosis. One week after fertilization, the larvae hatch from the eggs - tadpoles.They lead an aquatic lifestyle, have external gills, a two-chamber heart, one circle of blood circulation, organs of the lateral line, no paired limbs. Some amphibians take care of the offspring.

Comparative characteristics of a frog and a tadpole are presented in table 1.

General characteristics of amphibians

Table 1.

Comparative characteristics of frogs and tadpoles.

General characteristics of amphibians

The skin was covered with scales, there was a swimming blade on the tail, the remains of the gill cover. However, they already had five-fingered limbs, with the help of which they could periodically crawl onto the land and move along it.

The first amphibians appeared on Earth in the middle of the Paleozoic era. These were ichtiostegs. From them originated stegcepha  - An extensive group of ancient amphibians, which gave rise to modern amphibians.

Representatives of the class Earth-watershed are vertebrates, leading a water-land way of life. The ancestors of modern amphibians in the process of evolution were the first to land.

In connection with the development of amphibians new, ground-air environment, their external and internal structure has become more complicated. The extremities of modern amphibians consist of three sections, movably connected between themselves, which promotes active movement. Amphibians breathe lungsand wet skintherefore they live only in wet places. Amphibians three-chambera heart. The circulatory system has two circles of blood circulation.

Over the course of a long historical development, modern amphibian species have been formed. They are fewer than in other classes of vertebrates, about 4 thousand.

Leather

The skin of amphibians is bare, rich in glands. The glands secrete a lot of mucus, which reduces friction when swimming, and on land it protects the body from drying out. Skin plays an important role in breathing. Through the network of capillaries located in it, blood is saturated with oxygen and released from carbon dioxide. Poisonous twisted skin glands protect many amphibians from predators.

Tongue

Most amphibians have a sticky tongue that serves to catch small animals (insects, worms, slugs).

Eyes

When swallowing, the eyeballs help push the food bolus into the esophagus.

Amphibian eyes are protected from drying out and pollution for two centuries. The surface of the eye is moistened with the secret of a tear-gland. The cornea of ​​the eye is convex (and not flat, like in fish), the lens is in the form of a double-convex lens (and not round-like, like in fish), therefore land waters see farther than fish.

Skeleton

In the vertebrae of the amphibians two new divisions took shape - the cervical and the sacral. This ensures a mobile articulation of the head with the body.

The forelimb consists of three sections: ple-cha, forearm and hand. Back - from the thigh, lower leg and foot. Powerful muscles are attached to the bones of the limbs, allowing amphibians to actively move overland.

Breath

In terrestrial conditions, amphibians in the adult state breathe with lungs (they are poorly developed) and skin. In the water, they completely go to the skin respiration.

Circulatory system

The amphibian heart is three-chambered, consists of a ventricle and two atria. The blood moves along two circles of blood circulation: the small and the large. In a small circle, the blood flows from the ventricle to the lungs, where it is enriched with oxygen and returns to the left atrium, and from there to the ventricle. On a large circle, the blood from the ventricle delivers oxygen and nutrients to all organs of the animal, and from them takes carbon dioxide and metabolic products. Then the blood enters the right atrium, and then passes into the ventricle. Thus, in amphibians blood in the heart is mixed.

Metabolism

Due to the weak development of the lungs and the movement of mixed blood in the body, the level of metabolism in amphibians is low. Therefore they are cold blooded  animals. The temperature of their body corresponds to the ambient temperature. Under cooling conditions, the activity of amphibians decreases, and they fall into a stupor. Amphibians winter in shelters on land or in shallow water bodies.

Nervous system and sense organs

Complicated with amphibians nervous system  and the senses. The brain is well developed in the brain.

The organ of hearing is able to perceive sounds in the air. Amphibians form the middle ear with the eardrum and the auditory ossicles, which amplify the sound vibrations.

All amphibians are split apart. Fertilization is more often external. Females spawn eggs in the water, similar to fish eggs, which the male waters with milt. For some time, larvae hatch from their eggs, tadpoles that have many similarities with the larvae of fish. For several months, tadpoles go through the stages of individual development and turn into adult amphibians.

There are species with direct development among the middle-tailed amphibians. These are the Antilles and Caribbean leaf frogs. They lay eggs on the ground in wet places. Already in the egg, the embryo looks more like a frog than a tadpole. They are born fully formed.

The most numerous group of amphibians - representatives of the order Tailless. Some of them constantly live near the docks ( lake, pond, black-capped frogs).Others can leave the water for long distances ( moorish, grass frogs, toads)  or live in trees (frogs).

The frog, the most typical representative of amphibians, is the object of many laboratory experiments, for which a memorial was erected at the University of Sor-bonn (Paris). Another monument to the la carte is in Tokyo.  Material from the site

Most of the representatives of the Legless detachment ( cher) live in moist soil at a depth of 60 cm. To the order tailed belong salamander, newts, proteus, sirens.

Amphibians occupy a prominent place in the food chains of both aquatic and terrestrial ecosystems. Amphibians feed on insects and their larvae, as well as on spiders, molluscs, and fish fry. Among the insects that frogs and toads feed on, there is a large number of agents of agriculture and forestry. One frog over the summer can eat more than a thousand harmful insects. Many fish feed on amphibians.

Amphibians- These are the first vertebrates that could live on land, but also they did not part with the water element. Amphibians appeared about 350 million years ago. Their ancestors were ancient cross-fin fish. Amphibians are a numerous class of vertebrates. They number about 3.5 thousand species.   Modern amphibians are divided into three groups:

1. Legless;
2. Tailed;
3. Tailless.

Amphibians have many features that distinguish them from other animals. These are vertebrates that have a head, body, limbs, and some species have a tail (Fig. 1).

Fig. 1. The structure of amphibians ()

On the head is a pair of nostrils for breathing. There are eyes, they can be protected for centuries. Have a mouth. The skin is bare, moisturized with mucus. Amphibians can breathe light as well as skin. Some species have gills.

The body temperature of these animals depends on the ambient temperature, so they are active only in warm weather. When the temperature drops, they immediately fall into a stupor. There are in nature and poisonous individuals.

Amphibians breed, as well as fish, laying eggs. Eggs are not protected by the shell or skin, so amphibians usually breed in water. From amphibian eggs comes the larva, which looks very similar to fish. Further development takes place in the water with the transformation - metamorphosis. Metamorphosis  - This is a deep transformation of the structure of the body, transformation. Then, future amphibians lose gills, some individuals - even the tail. Then the limbs are grown and come out on land as an adult animal.

Amphibians eat exclusively mobile live food. They destroy in a huge number of insects and their larvae. They are found everywhere, excluding only too cold or hot zones of the Earth.

The most ancient and lived to our times thanks to their underground lifestyle are legless amphibians. There are about 150 species in nature. These include all tropical and very many aquatic worms. These amphibians are distinguished by their unusual body structure. These amphibians have a worm-like cylindrical body. The skin is bare, supplied with mucous poisonous glands. There are cross rings like earthworms. Animals have no limbs and tail. Their head is strong, small, imperceptibly turns into the torso. With it, the worms are laying in the wet ground of their own dungeons. In connection with the burrowing lifestyle, their eyes were under their skin. Amphibian food is sought by smell and touch. Eat snails, worms, larvae, insects. Lead a very hidden lifestyle, do not like sunlight. The most famous is the ringed worm (Fig. 2).

Fig. 2. Ringed Worm ()

Unlike other amphibians, they lay their eggs on land. The female rolls around the egg laying and moistens it with her mucus, incubates.

The fish stock in the skin has small imperceptible bone scales (Fig. 3).

Fig. 3. Fishmeat ()

The Central American worm does not lay eggs, it immediately gives birth to live calves.

Science is known   about 350 speciestailed amphibians. These animals look like lizards, only the skin is soft and completely devoid of scales. Tritons and salamanders belong to the caudate amphibians. In these animals, an elongated spindle-shaped body, which imperceptibly passes into a long tail. Bending the tail to the right and left helps to move in the water. On land, amphibians move with the help of two pairs of underdeveloped limbs. Fingers may have membranes and lack claws.

Sirens have only front limbs (Fig. 4).

Amphibians, constantly living in the water, breathe gills. In the mouth is the language, its shape is diverse. There are small teeth. Many tails have the ability to grow a new one when they lose their tail or legs. Amphibians do not know how to chew, they swallow food whole. Amphibians seize everything that moves, and do not take quite suitable for food fixed feed. Tailless amphibians feed on insects, grabbing them in motion with the help of a long sticky tongue. Tailed animals feed on worms and arthropods.

Footless amphibians find food by touch or use the sense of smell. They feed on insect larvae and worms.

Siberian salaver is one of the few amphibians that is not afraid to live in permafrost conditions (Fig. 5).

Fig. 5. Siberian subdued ()

The most well-known tail amphibian is the triton (Fig. 6). They look like little dragons. Hunt newts love at night.

The fire salamander is famous for its bright color (Fig. 7). What is interesting is that the shape, size, pattern on the body of salamanders in each individual is unique.

Fig. 7. Salamander ()

Axolotl resembles an adult larva (Fig. 8).

Fig. 8. Axolotl ()

In nature, there is the most numerous squad of amphibians - it is tailless amphibians. They number about 3 thousand species. This is the most famous person squad. These include toads, frogs, frogs, toads, garlic. Their body is short and squat. The head is wide, without a neck, goes into the body. There is no tail. Skin is bare, moisturized with secrets. On the head are a pair of mobile eyes. With the help of view amphibians are looking for prey. There is a pair of nostrils. Were limbs shorter back. They have membranes that help swim. On the ground amphibians jump, they lead an active lifestyle. Small teeth and sticky tongue, which develops in the mouth, help them catch prey.

Bullfrog is a predator (Fig. 9). She even attacks chickens and eats young ducklings. Her cry resembles the roar of a bull.

Fig. 9. Bullfrog ()

Suriname pipa is famous for carrying tadpoles in the cells on the back (Fig. 10). From them emerge adult frogs.

Fig. 10. Suriname pipa ()

The hairy frog is protected by sharp claws, like in a cat (fig. 11). Source)

Amphibians play great role in human life. They destroy a huge number of insects, thereby benefiting agriculture. They also eat insects, which are carriers of disease. Also amphibians are used in medical laboratory research. Man even breeds amphibians as a pet. In some countries they are even eaten.

Bibliography

1. Samkova V.A., Romanova N.I. The world around 1. - M .: Russian word.
2. Pleshakov A.A., Novitskaya M.Yu. The world around us 1. - M .: Enlightenment.
3. Gin A.A., Faer S.A., Andrzheevskaya I.Yu. The world around us 1. - M .: VITA-PRESS.

1. Worldofnature.ru ().
2. Floranimal.ru ().
3. Zoodrug.ru ().

Homework

1. Who are amphibians?
2. How amphibians breed?
3. What are the three amphibian detachments emit? Describe each squad amphibians.
4. * Prepare a story about the most unusual and interesting, in your opinion, representative of the class Amphibians.

General Characteristics Class Amphibians

General characteristics of the class. Amphibious - the first small group of species (2.1 thousand) of vertebrate animals that mastered the terrestrial environment, but retained a close relationship with the aquatic. Widespread, but most widely found in regions with warm and humid climates. They live near water.

Amphibians originated from one of the groups of ancient freshwater cross-finned fishes, called cephalus, which lived about 300 million years ago in swampy water bodies. The most important adaptations that allowed amphibians to reach the ground environment are associated with overcoming the force of gravity (gravity) and protecting the body from moisture loss.

Characteristic features of the organization of amphibians are as follows:

1. The body is slightly flattened and divided into the head, torso and two pairs of five-fingered limbs. A small group of amphibians has a tail.

2. The skin is thin, naked, moist, rich in mucous glands.

3. The skull is movably connected to the spine, which consists of four sections: cervical, trunk, sacral and caudal. The shoulder and pelvic girdle provides support for the limbs. The skeleton of the extremities is constructed according to the type of a system of moving levers, allowing an animal to move on a solid surface. There is a lot of cartilage in the skeleton.

4. The muscular system consists of separate differentiated muscles. The movements of different parts of the body are more diverse than in fish.

5. Amphibians - predators. They have developed salivary glands, the secret of which moisturizes the mouth, tongue and food. Actively caught prey is digested in the stomach. The last section of the alimentary canal is an expanded cloaca.

6. Respiratory organs of adult animals - the skin and lungs, in the larvae - the gills.

7. Three-chamber heart. There are two circles of blood circulation: large (trunk) and small (pulmonary). Mixed blood flows through the arteries of the systemic circulation, and only the brain is supplied with arterial blood.

8. Organs of excretion - paired trunk organs. Urine flows through the two ureters into the cloaca, and from it into the bladder. The output of the nitrogen metabolism is urea.

9. The forebrain of amphibians compared with that of fish is large and divided into two hemispheres. The cerebellum is worse developed due to low mobility. The structure of the organs of hearing and vision is adapted to life on land. The amphibian larvae have a lateral line organ.

10. Fertilization is external, in water. Development with incomplete metamorphosis, with the stage of a fish-like larva.

  Features of the structure and life processes

In more detail the structure of amphibians consider the example of a frog - a representative of the Tailless. The flattened body of a frog is subdivided into a wide head and a short torso. The head is inactive, as the neck is almost not expressed. Hind limbs longer than the front. The skin is bare, rich in multicellular mucous glands, attached to the body not all over, but only in certain areas, between which there are spaces filled with lymph. These features of the structure protect the skin from drying out.

The skeleton of amphibians, as in all vertebrates, consists of the skull, spine, skeleton of the extremities and their belts. The skull is almost entirely cartilaginous (Fig. 1). It is movably articulated with the spine. The spine contains nine vertebrae, united in three sections: cervical (1 vertebra), trunk (7 vertebrae), sacral (1 vertebra), and all caudal vertebrae have grown together, forming a single bone - urostyle. The ribs are missing. The shoulder girdle includes typical for terrestrial vertebral bones: paired shoulder blades, crow bones (coracoids), clavicle and unpaired sternum. It has the form of a semi-ring lying in the thickness of the trunk muscles, i.e. it is not connected to the spine. The pelvic girdle is formed by two pelvic bones formed by three pairs of iliac, sciatic and pubic bones, fused together. The long iliac bones are attached to the transverse processes of the sacral vertebra.

Figure 1. Frog skeleton: 1 - foot capacity; 2 - leg; 3 - the femur; 4 - Ilium; 5 - styling; 6 - sacral vertebra; 7 - cervical vertebra; 8 - skull; 9 - scapula; 10 - sternum; 11 - humerus; 12 - forearm; 13 - brush bones.

The skeleton of free limbs is built according to the type of a system of polynomial levers, movably connected by spherical joints. In the composition of the forelimb allocate shoulder, forearm and hand. In tailless amphibians, the elbow and radius are merged, forming the common bone of the forearm. The hand is divided into the wrist, metacarpus and four phalanges of the fingers. The hind limb consists of the thigh, lower leg and foot. The foot includes the bones of the tarsus, metatarsus and phalanges of the five fingers. Hind limbs longer than the front. This is due to the movement on land by jumping, and in the water - with the vigorous work of the hind limbs while swimming. As we see, such a scheme of the structure of the limbs is typical for terrestrial vertebrates and in each class has minor changes associated with the characteristics of their movement. Due to the mobility of the skeleton, body movements of amphibians are more diverse than in fish.

The muscular system of amphibians under the influence of the terrestrial lifestyle has undergone significant changes. Monotonously constructed muscle segments of fish are transformed into differentiated muscles of the limbs, head, and mouth that are involved in the process of ingestion of food, ventilation of the respiratory organs.

Differentiation of the digestive system of amphibians remained at about the same level as that of their ancestors, fish. The common oropharyngeal cavity passes into the short esophagus, behind it is a slightly detached stomach, which passes into the intestine without a sharp boundary. The intestine ends with the rectum, passing into the cloaca. The ducts of the digestive glands - the liver and pancreas - flow into the duodenum. In the oropharyngeal cavity, ducts of salivary glands, which are absent in fish and wetting the oral cavity and food, are opened. The terrestrial mode of life is associated with the appearance in the oral cavity of a real language - the main organ of food extraction. In frogs, it is attached to the front of the floor of the mouth and is able to quickly move forward, sticking prey. Adult frogs, like all other amphibians, are carnivorous and feed on moving small animals, sometimes caviar, fish fry.

Frogs breathe light and skin. The lungs are paired hollow bags with a cellular inner surface pierced by a network of blood capillaries, where gas exchange occurs. The respiratory mechanism in amphibians is imperfect, of an injection type. The animal draws air into the oropharyngeal cavity, for which it lowers the floor of the mouth and opens the nostrils. Then the nostrils are closed with valves, the floor of the mouth rises, and air is forced into the lungs. The removal of air from the lungs is due to the contraction of the pectoral muscles. The surface of the lungs in amphibians is small, less than the surface of the skin. Therefore, blood oxygenation occurs not only through the lungs, but also through the skin. So, the pond frog gets through the skin 51% oxygen. Being under water, amphibians breathe exclusively skin. In order for the skin to function on the ground as a respiratory organ, it must be moist.

The circulatory system of amphibians is represented by a three-chamber heart, consisting of two atria and a ventricle, and two circles of blood circulation - the large (trunk) and small (pulmonary) circuits. The pulmonary circulation starts in the ventricle, turns on the vessels of the lungs and ends in the left atrium. The big circle also begins in the ventricle. The blood, passing through the vessels of the whole body, returns to the right atrium. Thus, arterial blood from the lungs enters the left atrium, and venous blood from the whole body enters the right atrium. Arterial blood flowing from the skin also enters the right atrium. So thanks to the appearance of the pulmonary circle of blood circulation, arterial blood also flows into the heart of amphibians. Despite the fact that arterial and venous blood enters the ventricle, complete mixing of the blood does not occur due to the presence of pockets and incomplete septa. Thanks to them, as they exit from the ventricle, arterial blood flows through the carotid arteries to the head section, venous to the lungs and skin, and mixed to all other organs of the body. Thus, amphibians do not have complete blood separation in the ventricle, therefore the intensity of vital processes is low, and the body temperature is not constant.

The organs of excretion of amphibians, as well as in fish, are represented by the trunk buds. However, unlike fish, they have the form of flattened compact bodies lying on the sides of the sacral vertebra. In the kidneys there are glomeruli that filter out harmful decomposition products (mainly urea) from the blood and at the same time important substances for the body (sugars, vitamins, etc.). During runoff through the renal tubules, the body's beneficial substances are absorbed back into the blood, and urine enters the two ureters into the cloaca and from there into the bladder. After filling the bladder, its muscle walls are reduced, urine is discharged into the cloaca and discharged outside. The loss of water from the body of amphibians with urine, as well as in fish, is compensated by its intake through the skin.

The amphibian brain has the same five divisions as the fish brain. However, it differs from it by the great development of the forebrain, which in amphibians is divided into two hemispheres. The cerebellum is underdeveloped due to the low mobility and uniform nature of the movements of amphibians.

The emergence of amphibians on land influenced the development of the sense organs. Thus, amphibian eyes are protected from drying out and clogging with mobile upper and lower eyelids and a blinking membrane. The cornea has acquired a convex shape, and the lens - a lens-shaped. See amphibians mainly moving objects. A middle ear with one auditory ossicle (stapes) appeared in the organ of hearing. The middle ear cavity is separated from the environment by the eardrum and is connected to the oral cavity via a narrow canal, the Eustachian tube, due to which the internal and external pressure on the eardrum is balanced. The appearance of the middle ear is caused by the need to enhance the perceived sound vibrations, since the density of the air medium is less than that of water. The amphibian nostrils, in contrast to fish, are perforated and lined with sensitive epithelium that perceive odors.

Reproduction of amphibians has its own characteristics. The sex glands are paired. Paired oviducts fall into the cloaca, and the spermatic ducts into the ureters. Frogs breed in the spring of the third year of life. Fertilization takes place in water. After 7--15 days, fish-like larvae, tadpoles, develop in fertilized eggs. The tadpole is a typical aquatic animal: it breathes through the gills, has a two-chamber heart, one circle of blood circulation and a lateral line organ, and floats by means of a tail bordered by a membrane. In the course of metamorphosis, the larval organs are replaced by the organs of an adult animal.