The external structure of the frog briefly. frog animal

Amphibians- a small group of vertebrates, occupying an intermediate position between fish and true terrestrial chordates. The vast majority of amphibians live, depending on the stages of the life cycle, either in water or on land, therefore amphibians are classified as semi-aquatic, semi-terrestrial chordate animals. This class of terrestrial animals has retained a very close relationship with the aquatic environment.

The paired five-fingered limbs characteristic of terrestrial animals testify to the adaptability to a terrestrial way of life. Their limbs consist of three sections (the forelimb - from the shoulder, forearm and bone, the back - has a thigh, lower leg, foot). The hand and foot end in fingers. Breathe lightly and with moist skin. They have two circles of blood circulation and a three-chambered heart. They reproduce and develop in water. The larva is equipped with gills. Adult amphibians retain a number of traits inherited from their fish-like ancestors. First of all, this a large number of mucous glands in the skin that help keep it moist. The skin is an important respiratory organ in amphibians, but when dry, it cannot perform respiratory function, since oxygen diffusion occurs only through the water film. This explains the richness of the amphibian fauna in the warm and humid regions of the globe.

The origin of amphibians from fish is also evidenced by the method of reproduction. Amphibians lay eggs that are poor in nutrients and unprotected from the environment, as a result of which eggs can only develop in water. Just like fish, amphibians are characterized by external fertilization of eggs. An even greater resemblance to fish is found in amphibian larvae - tadpoles. Their respiratory organs are gills, first external, then internal; the heart of the larvae is two-chambered and one circle of blood circulation. The organ of the lateral line is preserved on the body, the organ of movement is the tail, surrounded by a swimming membrane.

pond frog

Adult amphibians, typified by pond frog, has a short and wide body. The neck is not pronounced. Above the mouth are the nostrils, a little behind - the eyes, which have eyelids that protect the eyes from drying out (adaptation to life on land). Behind the eyes are the organs of hearing, consisting of the middle ear, closed by the tympanic membrane, and the inner ear. The body rests on two pairs of limbs. The rear ones are the most developed. With their help, the frog moves by jumping on land and swims well. This is facilitated by the presence of a swimming membrane between the fingers.

frog skeleton

frog skeleton consists of a small brain box(evidence of poor brain development) and short spine. The skeletons of the limbs consist of three sections, which are mobile due to the connection with the help of joints. The forelimb is attached to the shoulder girdle, which consists of chest, two crow bones, clavicle and two shoulder blades. The hind limbs are connected to the spine by pelvic girdle, formed by fused pelvic bones. The muscles of the frog are especially developed in the region of the belts and especially in the free limbs.

Digestive system of a frog

Digestive system of a frog very similar to that of fish, only in amphibians hindgut does not open outwards, but into its special extension - cloaca. The cloaca open ureters and excretory ducts reproductive organs. The frog catches its prey with the help of sticky tongue, which is attached in the mouth by the anterior end. The frog usually swallows the captured food (insects) whole

Frog respiratory organs

Frog respiratory organs - lungs and wet skin. Through nostrils air enters the oral cavity, and from there - into lungs. Exhalation occurs as a result of contractions of the muscles of the ventral side of the frog. Mucus-covered skin with a well-developed capillary system promotes skin respiration.

Frog circulatory system

Circulatory system frogs has a more complex structure. Appearance two circles of blood circulation led to a more complex structure. hearts. It consists of three chambers: ventricle and two atrial. The right atrium contains only venous blood saturated with carbon dioxide, and the left atrium contains only arterial blood; blood mixes in the ventricle. Arterial, oxygenated blood is supplied to the brain of the frog, while the whole body receives mixed blood. Through a large circle of blood circulation, blood from the ventricle is sent through the arteries to all organs and tissues, and from them through the veins flows into the right atrium. Through the pulmonary circulation, blood from the ventricle enters the lungs and skin, and from the lungs returns to the left atrium.

Frog excretory organs

Frog excretory organs - kidneys, ureters, bladder. The kidneys produce urine, which flows through the ureters to the cloaca, and from it to the bladder. As it fills, urine is removed through the cloaca to the outside.

Nervous system of a frog

Central nervous system of amphibians consists of the same sections as in fish, but the forebrain is more developed, it can be distinguished large hemispheres. The cerebellum is less developed than in fish, due to the simpler and more uniform movements of amphibians.

Reproduction and development of the frog

After waking up from hibernation, frogs leave deep water bodies, moving to shallow ponds, ditches, puddles and floods of melt water well warmed up by the sun. Here the females spawn, very similar to fish eggs, and the males pour their seminal fluid over it. Spermatozoa penetrate the eggs and fertilize them. The shells of eggs in water swell greatly, become transparent, stick together with each other, forming lumps, and float to the surface or attach to underwater objects. After fertilization, the larvae begin to develop rapidly, as a result, a multicellular germ. After 12-25 days, a larva appears from the egg - tadpole.

The tadpole initially has a tail and resembles a fish fry. Its tail is surrounded by a thin swimming membrane. The tadpole breathes with three pairs of feathery gills located on the sides of the head. It has lateral line organs in its skin. The mouth and limbs are initially absent. After some time, a mouth begins to erupt with two horny plates and denticles on the lips, with which the tadpole scrapes off the plants that serve as food for it. Then the outer gills disappear and the inner gills develop. At this stage of development, the tadpole is especially similar to a fish. At this time, he developed a chord, a two-chambered heart and one circle of blood circulation. In further development, lungs, a three-chambered heart, and two circles of blood circulation appear. Next come the hind and forelimbs. First, it becomes thinner, and then shortened, then the tail disappears completely, and the tadpole turns into a small frog. This process lasts 3-4 months and is called metamorphosis. Sexual maturity in frogs occurs in the third year of life.

Seasonal natural phenomena affect life cycle amphibians. So, due to the conditions of seasonal climatic changes, their annual cycle is divided into such periods: spring awakening, spawning period(breeding), summer activity period and hibernation, hibernation can be terrestrial (newts) and underwater (frogs).

frog habitat

Frogs live in damp places: in swamps, wet forests, meadows, along the banks of freshwater reservoirs or in water. The behavior of frogs is largely determined by humidity. In dry weather, some species of frogs hide from the sun, but after sunset or in wet, rainy weather, it is time for them to hunt. Other species live in the water or near the water itself, so they hunt during the day.

Frogs feed on various insects, mainly beetles and Diptera, but also eat spiders, terrestrial gastropods, and sometimes fish fry. Frogs lie in wait for their prey, sitting motionless in a secluded place.

When hunting, sight plays a major role. Noticing any insect or other small animal, the frog throws out a wide sticky tongue from its mouth, to which the victim sticks. Frogs grab only moving prey.

Figure: Frog tongue movement

Frogs are active in the warm season. With the onset of autumn, they leave for the winter. For example, the common frog hibernates at the bottom of non-freezing reservoirs, in the upper reaches of rivers and streams, accumulating in tens and hundreds of individuals. The sharp-faced frog climbs into cracks in the soil for wintering.

The body of the frog is short, a large flat head without sharp borders passes into the body. Unlike fish, the head of amphibians is movably articulated with the body. Although the frog does not have a neck, it can tilt its head slightly.

Figure: External structure of a frog

Two large bulging eyes are visible on the head, protected over the centuries: leathery - upper and transparent mobile - lower. The frog blinks frequently, while the moist skin of the eyelids wets the surface of the eyes, protecting them from drying out. This feature has developed in the frog in connection with its terrestrial lifestyle. Fish whose eyes are constantly in the water do not have eyelids. A pair of nostrils is visible in front of the eyes on the head. These are not only the openings of the olfactory organs. The frog breathes atmospheric air, which enters its body through the nostrils. The eyes and nostrils are located on the upper side of the head. When the frog hides in the water, it exposes them to the outside. At the same time, she can breathe atmospheric air and see what is happening outside the water. Behind each eye on the frog's head is a small circle covered with skin. This is the outer part of the organ of hearing - eardrum . inner ear frogs, like fish, are located in the bones of the skull.

The frog has well-developed paired limbs - front and hind legs. Each limb consists of three main sections. In the front leg, there are: shoulder, forearm and brush. In a frog, the hand ends with four fingers (its fifth finger is underdeveloped). In the hind limb, these sections are called hip, shin, foot. The foot ends with five toes, which in a frog are connected by a swimming membrane. The parts of the limbs are movably articulated with each other by means of joints. The hind legs are much longer and stronger than the front legs, they play a major role in movement. The sitting frog rests on slightly bent forelimbs, while the hind limbs are folded and located on the sides of the body. Quickly straightening them, the frog makes a jump. The front legs at the same time protect the animal from hitting the ground. The frog swims by pulling and straightening the hind limbs, while the front ones are pressed to the body.

The skin of all modern amphibians is naked. In a frog, it is always moist due to the liquid mucous secretions of the skin glands.

Water from environment(from reservoirs, rain or dew) enters the body of the frog through the skin and with food. The frog never drinks.

The frog skeleton consists of the same main sections as the perch skeleton, however, due to the semi-terrestrial lifestyle and leg development, it differs in a number of features.

Pattern: Frog Skeleton

Unlike fish, frogs have a cervical vertebrae. It is movably articulated with the skull. It is followed by trunk vertebrae with lateral processes (the frog's ribs are not developed). The cervical and trunk vertebrae have upper arches that protect spinal cord. A long tail bone is placed at the end of the spine in a frog and in all other anurans. In newts and other tailed amphibians, this section of the spine consists of a large number of movably articulated vertebrae.

The frog skull has fewer bones than the fish skull. In connection with lung breathing frogs don't have gills.

The skeleton of the limbs corresponds to their division into three sections and is connected to the spine through the bones of the limb belts. Forelimb belt - sternum, two crow bones, two collarbones and two spatulas- has the form of an arc and is located in the thickness of the muscles. Rear limb belt formed by fused pelvic bones and is attached tightly to the spine. It serves as a support for the hind limbs.

The internal structure of a frog

frog muscles

The structure of the muscular system of a frog is much more complicated than that of a fish. After all, the frog not only swims, but also moves on land. Thanks to contractions of muscles or groups of muscles, the frog can perform complex movements. Her limb muscles are especially well developed.

Digestive system of a frog

The digestive system of amphibians has almost the same structure as that of fish. Unlike fish, the hindgut does not open directly outward, but into a special extension of it, called cloaca. The ureters and excretory ducts of the reproductive organs also open into the cloaca.

Figure: The internal structure of a frog. Digestive system of a frog

Respiratory system of a frog

The frog breathes atmospheric air. The lungs and skin are used for breathing. The lungs look like bags. Their walls contain a large number of blood vessels in which gas exchange takes place. The frog's throat is pulled down several times per second, which creates a rarefied space in the oral cavity. Then the air enters through the nostrils into the oral cavity, and from there into the lungs. It is pushed back under the action of the muscles of the body walls. The frog's lungs are poorly developed, and skin respiration is just as important for it as pulmonary respiration. Gas exchange is possible only with wet skin. If a frog is placed in a dry vessel, its skin will soon dry out and the animal may die. Immersed in water, the frog completely switches to skin respiration.

Figure: The internal structure of a frog. Circulatory and respiratory system frogs

The circulatory system of a frog

The frog's heart is placed in front of the body, under the sternum. It consists of three chambers: ventricle and two atria. Both atria and then the ventricle contract alternately.

In the frog's heart, the right atrium contains only venous blood, left - only arterial, and in the ventricle the blood is mixed to a certain extent.

The special arrangement of the vessels originating from the ventricle leads to the fact that only the brain of the frog is supplied with pure arterial blood, while the whole body receives mixed blood.

In a frog, blood from the ventricle of the heart flows through the arteries to all organs and tissues, and from them it flows through the veins into the right atrium - this big circle blood circulation. In addition, blood flows from the ventricle to the lungs and skin, and from the lungs back to the left atrium of the heart - this pulmonary circulation. All vertebrates, except fish, have two circles of blood circulation: a small one - from the heart to the respiratory organs and back to the heart; large - from the heart through the arteries to all organs and from them back to the heart.

Metabolism in amphibians on the example of frogs

The metabolism of amphibians is slow. The body temperature of a frog depends on the ambient temperature: it rises in warm weather and drops in cold weather. When the air becomes very hot, the frog's body temperature drops due to the evaporation of moisture from the skin. Like fish, frogs and other amphibians are cold-blooded animals. Therefore, when it gets colder, the frogs become inactive, tend to climb somewhere warmer, and for the winter they completely hibernate.

The central nervous system and sense organs of amphibians on the example of a frog

The central nervous system and sense organs of amphibians consist of the same departments as those of fish. The forebrain is more developed than in fish, and two swellings can be distinguished in it - large hemispheres. The body of amphibians is close to the ground, and they do not have to maintain balance. In this regard, the cerebellum, which controls the coordination of movements, is less developed in them than in fish.

Figure: The internal structure of a frog. Nervous system frogs

The structure of the sense organs corresponds to the terrestrial environment. For example, by blinking its eyelids, the frog removes dust particles adhering to the eye and moistens the surface of the eye.

Like fish, frogs have an inner ear. However, in the air sound waves spread much worse than in water. Therefore, for better hearing, the frog has developed more middle ear. It begins with the tympanic membrane that perceives sounds - a thin round film behind the eye. From it, sound vibrations are transmitted through the auditory ossicle to the inner ear.

Answer left Guest

Signs of adaptability of amphibians to life on land:
1. The body is short.
2. Movable connection of the head with the body.
3. Eyelids.
4. Nostrils.
5. Development of the hind limbs.
6. The skin secretes mucus.
Signs of adaptability of amphibians to life in water:
1. Streamlined body shape.
2. Eyes and nostrils on the top side of the head.
3. Swimming membranes.
4. The skin is bare.
The frog blinks frequently, while the moist skin of the eyelids wets the surface of the eyes, protecting them from drying out. This feature has developed in the frog in connection with its terrestrial lifestyle. Fish whose eyes are constantly in the water do not have eyelids. A pair of nostrils is visible in front of the eyes on the head. These are not only the openings of the olfactory organs. The frog breathes atmospheric air, which enters its body through the nostrils. The eyes and nostrils are located on the upper side of the head. When the frog hides in the water, it exposes them to the outside. At the same time, she can breathe atmospheric air and see what is happening outside the water. Behind each eye on the frog's head is a small circle covered with skin. This is the outer part of the organ of hearing - the tympanic membrane. The inner ear of the frog, like that of fish, is located in the bones of the skull.
The foot ends with five toes, which in a frog are connected by a swimming membrane. The parts of the limbs are movably articulated with each other with the help of joints. The hind legs are much longer and stronger than the front legs, they play a major role in movement. The sitting frog rests on slightly bent forelimbs, while the hind limbs are folded and located on the sides of the body. Quickly straightening them, the frog makes a jump. The front legs at the same time protect the animal from hitting the ground.
The skin of all modern amphibians is naked. In a frog, it is always moist due to the liquid mucous secretions of the skin glands.

Water from the environment (from reservoirs, rain or dew) enters the body of the frog through the skin and with a niche. The frog never drinks.

From The Tree of Knowledge magazine

Here you can download a pdf-file with pictures (268 kb): Frogs. Or read the text:

Frogs and their close relatives, toads, are amphibious creatures.

e. Vertebrates, spending part of their life on land, and part in the water. Most of the 3.5 thousand amphibians are frogs.

From a biological point of view, there is almost no difference between frogs and toads. Frogs have more smooth skin, the hind legs are longer and the webs between the toes are well developed. Toads have a more rounded body, dry, often warty skin, and short hind legs suitable for crawling and short hops.

The membranes on their hind legs are underdeveloped, since water is not their element. Frogs and toads belong to the order of tailless amphibians that appeared on the planet about 150 million years ago.

Appearance

The body temperature of cold-blooded frogs is always equal to the ambient temperature, so they are cold and slippery to the touch. The head of the frog is wide and flat, with a very wide mouth. She has 4 fingers on her front paws, 5 on her hind legs. The fingers are connected by a thin leathery membrane.

In some aquatic species, the thumbs of the hind legs are armed with sharp claws for tearing prey. Most frogs are nocturnal.

Ways of transportation

Thanks to its long and strong legs, the frog jumps excellently. To do this, it first rises on its front legs, and then, powerfully pushing off with its hind legs, takes off into the air. Webbed frogs spend almost their entire lives in the water. Some tree-dwelling frogs are not webbed, but have a round sucker at the tip of each finger.

Its surface covered with rough skin allows the frog to easily climb the tree bark.

reproduction

Almost all frogs lay their eggs in water.

Control and generalizing lesson in the form of the game "Lucky chance" on the topic "Class Amphibians"

In one lump of caviar, there are several thousand small - a few millimeters in diameter - eggs, each of which is enclosed in a foamy protective shell. The shell protects the eggs from predators, but some frogs have developed their own methods of nursing offspring. They lay much fewer eggs, but they take care of them sparing no effort. So, before the start of the rainy season, the blacksmith frog fences off a small pond near the shore of the reservoir, where he lays his eggs. Tadpoles appear there in complete safety, and with a flash flood swim away into a river or lake.

Development of tadpoles

The hind legs of the tadpole are formed at the base of the tail. The forelimbs are still hidden under the gill covers for some time and break out later, and not always at the same time, so it is not uncommon to see three-legged tadpoles.

Having acquired all the limbs, the tadpole becomes more and more like a frog. The shape of the mouth changes, the eyes protrude, the tail turns into a short process. At this stage of development, the frog decides to get out of the water for the first time.

Some frogs lay their eggs on land, under foliage or rocks. A few weeks later, bypassing the tadpole stage, they hatch into fully formed frogs. Certain types of frogs show real miracles of parental care. For example, the helmet-headed frog living on land, as well as the males of some South American poison dart frogs, bear eggs on their backs, where offspring are hatched from them.

Kids in a backpack

Some tree frogs, including the marsupial tree frog, have stepped even further in this responsible business. On the back of the female there is a capacious bag, where a caring father helps to place the eggs.

Tadpoles develop right in the bag, living off the yolk reserves in the stomach, and after a few weeks, tiny copies of happy parents appear from the backpack.

Food

The basis of the frog diet is live mobile prey, primarily insects, the size of which depends on the width of the mouth and the dimensions of the hunter himself. So, the American bullfrog eats everything that it can swallow, including poisonous snakes, giant centipedes, scorpions, and even its relatives.

Seeing the victim, the frog overtakes it with a lightning throw. Adhering to the sticky tongue, the prey is swallowed whole, while the frog blinks frequently, and eyeballs descend into the oral cavity, helping to push food down the pharynx.

self defense

Frogs are a tasty treat for many animals, and in order to protect themselves from predators, they have to indulge in all sorts of tricks. Some boldly rush to the enemy with a wide-open toothless mouth.

This technique is especially effective in the performance of a bullfrog, in which a human fist is freely placed in its mouth. Not every predator can resist such a psychic attack. Other species rely on camouflage or, conversely, flashy coloration.

So, many tree frogs cannot be distinguished from a leaf or a piece of bark when they are motionless, but in a jump, a bright spot on the abdomen or hind legs suddenly flashes before the predator’s eyes, and the frog’s moment of confusion is enough to hide.

popular delicacy

Culinary experts in many countries of the world consider frogs an exquisite delicacy. For example, in French restaurants, frog legs are served as a signature dish. However, the edible frog has become such a rarity these days that huge quantities of frogs are being imported from Asia to meet growing demand. In North America, the bullfrog, with its fleshy hind legs, is highly valued.

They usually go out to collect frogs at night, blinding them with the beam of a pocket flashlight.

137. Look at the pictures. Write the names of the body parts of the frog. What organs are located on her head? Write their names.

138. Study the table “Class Amphibians. The structure of the frog. Consider the drawing. Write names internal organs frogs marked with numbers.

Describe the structure of the amphibian brain.
The amphibian brain has more progressive features: larger forebrain, complete separation of the hemispheres. midbrain relatively small. The cerebellum is small, as amphibians have monotonous movements. 10 pairs of cranial nerves leave the brain.

Parts of the brain: anterior, middle, cerebellum, oblong, intermediate.

140. Study the table “Class Amphibians.

The structure of the frog. Consider the drawing. Write the names of the parts of the frog skeleton, indicated by numbers.

1. skull
2. shoulder blade
3. shoulder
4. forearm
5. brush
6. foot
7. lower leg
8. thigh
9. urostyle
10.

spine.

141. Look at the picture. Write the names of the parts digestive system frogs marked with numbers. How is the process of digestion carried out in frogs?

All amphibians feed only on moving prey.

At the bottom of the mouth is the tongue. When catching insects, it is thrown out of the mouth, prey sticks to it. The upper jaw has teeth that serve only to hold prey. When swallowing, the eyeballs help push food into the esophagus from the oropharynx.
The ducts open into the oropharynx salivary glands, the secret of which does not contain digestive enzymes.

From the oropharynx cavity, food enters the stomach through the esophagus, from there into the duodenum. The ducts of the liver and pancreas open here. Digestion of food takes place in the stomach and duodenum. Small intestine passes into the rectum, which forms an extension - the cloaca.

Draw a diagram of the structure of a frog's heart. What kind of blood is called arterial and what kind is called venous?
Arterial blood comes from the lungs and is rich in oxygen. Venous blood goes to the lungs.

Describe the process of reproduction and development of a frog. Point out the similarities in the reproduction of amphibians and fish.
Amphibians breed in shallow, well-warmed areas of water bodies. The reproductive organs in males are the testes, in females the ovaries. Fertilization is external.

Features of the structure of the frog

Frog development:
1 - egg;
2 - tadpole at the time of hatching;
3 - development of fin folds and external gills;
4 - stage of maximum development of external gills;
5 - stage of disappearance of the external gills; 6 - stage of the appearance of the hind limbs; 7 - stage of dismemberment and mobility of the hind limbs (forelimbs shine through the integument);
8 - stage of release of the forelimbs, metamorphosis of the oral apparatus and the beginning of resorption of the tail;
9 - landfall stage.

Fill the table.

The structure and significance of the sense organs of the frog.

145. Perform laboratory work "Features of the external structure of the frog in connection with the lifestyle."
1. Consider the features of the external structure of the frog. Describe the shape of her body, the color of her back and abdomen.
The body of a frog is divided into head, trunk and limbs.

Long hind legs with webbing between the toes allow it to jump on land and swim in the water. On the flattened head of the frog there is a large oral fissure, large bulging eyes and a pair of nostrils located on elevations. On the sides of the head behind the eyes are rounded eardrums (hearing organs). The frog's eyes are large and protruding. The eyes are equipped with movable eyelids. Male green frogs have resonators, or vocal sacs, in the corners of their mouths, which swell when croaking, amplifying sounds.
The skin of amphibians is naked and moist, covered with mucus.

Body coloring helps to defend against enemies.
2. Make a drawing of the frog's body, label its sections.

3. Consider the structure of the fore and hind limbs. Sketch them.

4. Consider the frog's head.

What sense organs are located on it?
see table. №144
5. Note the structural features of the frog associated with life in water and on land.
In water: skin is bare, covered with mucus.

There are nostrils on the head and eyes on the top. On the paws - swimming membranes. Hind legs long. Development and reproduction in water. In water it changes to cutaneous respiration. Cold-blooded. The larva has structural features similar to fish.
On land: 2 pairs of limbs, moves. Breathe with lungs. Feeds on insects. The heart is three-chambered.
Conclusions: Amphibians are the first Chordates to land on land. They still have features of external and internal structure, allowing them to partially live in the water, however, they also have progressive structural features characteristic of terrestrial animals.

Types of frogs and features of their content

The drug is considered to study the structure of the multilayer epithelium of the skin of amphibians living in other

Rice.

47. Stratified epithelium of the frog skin (magnification - approx. 10, v. 40):

1-cuticle, 2-stratum corneum, 3-germ layer, 4-pigment cells, 5-connective tissue

conditions than most mammals (should be compared with the previous preparation).

A piece of frog skin is fixed in 10% formalin, cross-sectioned, stained with alum hematoxylin and eosin.

At low magnification, the epidermis should be found.

It is necessary to study the preparation at high magnification. The epidermis consists of 5-8 rows of cells; adjacent to the basement membrane are high prismatic cells with a large oval nucleus.

These are the so-called basal cells. The next rows of cells no longer have this correct location and gradually flatten, so that the cells of the second layer are cubic, and the subsequent ones are flatter; the nuclei of the cells are correspondingly flattened. Light gaps are clearly visible between cells - intercellular gaps pierced by protoplasmic bridges.

All of the listed rows of cells form a germ layer, the cells of which are capable of reproduction.

On the germ layer there is a stratum corneum, consisting of one row of keratinized cells, clearly visible on the preparation, because they are colored orange.

The cells of the stratum corneum are flat with narrow long light nuclei, which are in the stage of degeneration, closely adjacent to each other, so that the boundaries between them are not visible. Their outer edge keratinizes most strongly and forms a thin cuticle. The stratified squamous epithelium of the skin of a frog, like that of other amphibians, keratinizes much weaker than the epidermis of a rat.

This is due to the fact that amphibians live in a humid environment and, in addition, their protective function is performed by mucus produced by special glands and covering the skin with a thick layer.

Directly under the epidermis in the connective tissue are pigment cells, completely filled with black pigment grains.

how many fingers do frogs have?

Answer left Guru

Features of the structure of amphibians and their life processes.

Consider the features of amphibians using the example of an ordinary frog - a representative of the Tailless order. The body of the frog is flattened and has a wide head and a short torso.

The head of the frog is inactive, since the cervical region is poorly expressed. The hind limbs (legs) are much longer than the front

The frog has bare skin studded with multicellular mucous glands that is not attached to the body over its entire surface.

The skin connects to the body in certain places, between which there is a space filled with lymph. This feature allows the frogs not to dry out on dry land.

The amphibian skeleton consists of a skull, spine, limbs and their girdles.

The skull consists almost entirely of cartilage and is movably connected to the spine. The spine consists of 9 vertebrae, which are combined into three sections:

- cervical (1 vertebra);

- trunk (from 2 to 8 vertebra);

- sacral (9th vertebra).

The tail vertebrae of the frog are fused to form a single bone called the urostyle.

The frog has no ribs. The shoulder girdle includes paired shoulder blades, coracoids (crow bones), clavicles and an unpaired sternum. The sternum has the form of a semicircle, which lies in the thickness of the trunk muscles and is not connected to the spine.

The pelvic girdle of a frog consists of two pelvic bones formed from three pairs of fused iliac, ischial, and pubic bones. Long ilium join the transverse processes of the sacral spine.

Features of the structure of the frog

Appearance

The body of a frog is subdivided into the head, trunk, forelimbs and longer hind limbs (adaptation for jumping). The neck is not outwardly expressed. The forelimb consists of the shoulder, forearm and hand, ending in 4 fingers, the hind limb consists of the thigh, lower leg and foot with 5 - 6 long fingers connected by a thin leathery fold - a swimming membrane (adaptation for swimming). At the base of the first (inner) finger of the male's forelimb there is a swelling - a genital wart, which helps to hold the female during mating.

On the sides of the wide flattened head are large convex eyes, equipped with inactive - upper and well mobile lower eyelids (open and close the eyelids on a dead frog with tweezers; look at the movement of the eyelids on a living one).

Toward the end of the muzzle are paired external nasal openings - nostrils. Behind the eyes, above the corner of the mouth, there is a rounded area of skin stretched over a semi-ossified cartilaginous ring; This is the tympanic membrane that covers the entrance to the middle ear cavity. From the inside to the center of the tympanic membrane is attached to the auditory bone - the stirrup.

In the corners of the mouth, male green frogs have thin folds of skin - vocal sacs, or resonators that inflate when croaking (if you press your finger on the sides of the body of a living male behind the forelimbs, then the resonators inflate in the form of thin-walled spherical swellings).

Appearance of a male pond frog:

1 - nostril, 2 - tympanic membrane, 3 - resonator, 4 - dorsal-lateral folds, 5 - cloacal opening

In male brown frogs, small resonators are hidden under the skin; when croaking, they, inflating, lift the skin below the corners of the mouth.

On the sides of the body, frogs of the genus Rana have longitudinal thickenings of the skin - dorsal-lateral folds. From above, at the end of the body, there is an opening of the cloaca.
The ventral side of the body in frogs is light, the dorsal side is darker, of a protective color.

In brown frogs, a black stripe runs from the eye back through the eardrum, masking the eye. Soft, thin, rich in mucous glands, the skin is devoid of scales and is very mobile (it is easily pulled away from the body) due to large subcutaneous lymphatic cavities located almost throughout the body.

Scheme of the structure of the skin of a frog (section):

1 - epidermis, 2 - corium, 3 - glandular cells of the skin gland,
4 - muscular cover of the gland, 5 - excretory duct of the skin gland,
6 - pigment cells

Under the multilayered epidermis lies corium - a fibrous connective tissue layer of the skin, in which pigment cells are scattered.

In contrast to fish, in amphibians, metameric muscles are greatly reduced - only relatively weakly developed portions of muscles along the spine are preserved from it. Basically, the muscular system is arranged according to the principle of portioned muscles - highly differentiated portions of muscles perform various, highly specialized functions. This type of muscle structure is best suited to the task of performing complex movements in a terrestrial environment.

The structure of the oral cavity

Cut the joints at the corners of the mouth with scissors, open the oral cavity wide and examine its structure.

First of all, the dimensions of the oral cavity and the wide section of the mouth are striking; this facilitates the capture of prey and is important for respiration.

Small homogeneous teeth adhere to the inner lateral surface of the upper jaw; on the mandible no teeth.

frog oral cavity:

1 - teeth, 2 - tongue, 3 - vomer with vomer teeth, 4 - choanae,
5 - translucent eyeball, 6 - opening of the Eustachian tube,
7 - larynx, 8 - resonator hole

Muscular, sticky, forked at the free end, the tongue is attached with its front end to the anterior end of the lower jaw and can be thrown out of the mouth when catching prey.

On the palate (the roof of the oral cavity), small bones are clearly visible - vomers with small vomer teeth sitting on them. In front of the vomers are the paired openings of the internal nostrils, or choanae. After inserting the end of the needle into them, make sure that they communicate with the external nasal openings.

Frog breeding and care

In the center of the palate, the eyeballs are well translucent; while reducing eye muscles the eyes can protrude into the mouth, helping to push food up the esophagus. Slightly pressing on the eyes from above, see how deeply they can be pressed into the oral cavity. In the depths of the oral cavity, near the jaw joints, there are openings of the Eustachian tubes leading to the middle ear cavity; a needle inserted into the opening of the Eustachian tube exits through the eardrum.

In the fork between the posterior tips of the tongue at the bottom of the oral cavity, a slight elevation with a longitudinal slit is visible - the larynx, formed by paired arytenoid cartilages.

Air enters the lungs through the larynx. At the bottom of the mouth near the corners of the mouth, males have small openings leading to resonators. Behind the laryngeal fissure, the oral cavity imperceptibly passes into a wide esophagus.

The sequence of the opening of the frog.

A - cut the skin; B - cut the wall of the body; B - unscrew the walls of the body:
1 - intermaxillary muscles, 2 - muscles of the shoulder girdle,
3 - muscles abdominal wall, 4 - abdominal vein; dotted line - cut lines

Amphibians, or amphibians, are cold-blooded predatory animals that feel great both in water and on land. Initially, they breathe with the help of gills, and then adults switch to pulmonary breathing. The article will consider in detail the internal structure of amphibians using the example of a frog.

Habitat

Amphibians live in two environments: on land and in water, they jump well and swim well and even climb trees. Due to their characteristics, they feel great both in damp places (swamps, wet forests and meadows), and on the banks of freshwater reservoirs. The whole process of development takes place in water. There they reproduce, the development of larvae takes place, as well as the growth of fry, and only mature individuals are found on land.

The behavior of frogs also depends on the humidity of the environment. They do not tolerate sunny weather, and in the evening and rainy days go hunting. Those that live in water or near it look for food even during the daytime. With the onset of cold weather, animals burrow into the silt at the bottom of reservoirs and spend the entire cold season there. They can breathe through their skin, so there is no need to rise to the surface. Some animals spend the winter season on the surface of the earth, burrowing under heaps of fallen leaves and large stones. All processes in the body slow down and only with the advent of heat do they return to normal life even from a frozen state.

Characteristics of the external structure of the frog

Schoolchildren usually study the internal structure of a frog in the 7th grade. However, first let's get acquainted with the external structure. The body of a frog consists of a head and a body from 8 mm to 32 cm long. The color can be monophonic (green, brown, yellow) or variegated. cervical not expressed, the head immediately passes into the body. The animal has developed fore and hind limbs. Skin naked and mucous, horny are poorly developed. The epidermis contains a large number of multicellular glands that produce a mucous substance that protects the skin from drying out. The typically terrestrial limbs of the five-toed type have a complex muscular structure. The hind limbs, due to a special way of movement, have received a stronger development than the front ones, which consist of the shoulder, forearm and hand. There are four fingers, in males, on the basis of the internal one, there is a swelling, which is a genital wart. The long hind limb consists of the thigh, lower leg and foot, which has five fingers connected by a swimming membrane.

frog head

On a flat head there are:

The external and internal structure of the frog

A frog, like all amphibians, can be without water for a long time, but it needs it for reproduction. Having changed, the larvae lose their resemblance to fish and turn into amphibians. The body is elongated, there are two pairs of limbs. The head, which passes into the body, unlike fish, is able to turn. The skeleton consists of bones, although there is a lot of cartilage; The spine has many vertebrae. There are no ribs, and hence chest- No. Thanks to a strong skeleton and developed muscles, the animal is adapted for life on land. The hind and forelimbs have three joints each. The skin is smooth, contains many glands to moisturize it. The frog breathes through the lungs and skin.

The structure of the internal organs of the frog suggests the presence of a three-chambered heart, consisting of one ventricle and two atria, as well as two circles of blood circulation. Food passes from the pharynx through the esophagus, stomach into the small intestine. For its digestion, secrets are produced by the liver, the walls of the stomach and the pancreas. At the end of the rectum is the cloaca, into which the female's oviduct opens. Animals have two kidneys and a bladder. The small braincase contains a developed forebrain and cerebellum. Frogs have organs of sight, hearing, touch, taste, smell.

The internal structure of a frog

Muscles have a fairly complex structure and are quite well developed compared to fish. Thanks to well-coordinated work the frog's muscle groups can move, and in addition, they also take part in breathing.

The skeleton includes the following sections: spine, girdles and limb skeleton, skull. The latter is connected to the spine with the help of a cervical vertebra. This allows you to tilt your head. There are seven vertebrae in the trunk region, no ribs. The sacral, like the cervical, is represented by one vertebra. long bone forms the tail. The thighs, shins, feet form the hind limbs, and the shoulders, forearms and hands form the forelimbs. They are connected to the spine by means of a limb belt: anterior and posterior. The first includes two shoulder blades and the sternum, and the second - the pelvic bones, which are fused together.

Nervous system

More complex than that of fish is the nervous system of a frog. Its internal structure is as follows: nerves, spinal cord and brain. The latter has three sections: a more developed, compared with fish, forebrain and a small cerebellum, since frogs lead a sedentary lifestyle and make only monotonous movements, as well as large hemispheres. Adults have developed upper and lower eyelids, as well as a nictitating membrane, thanks to which the cornea does not dry out and is protected from pollution.

Circulatory system

The circulatory system is represented by a three-chambered heart. From the lungs arterial blood enters the left atrium. Venous blood enters the right atrium from the internal organs, and arterial blood from the dermis.

With simultaneous contraction of the atria, blood enters the ventricle. With the help of a special valve, venous blood enters the lungs and skin, and arterial blood goes to the brain and head organs. Mixed blood enters all other organs, as well as parts of the body. The frog has two circles of blood circulation, and they are united by a common ventricle.

Respiratory system

The skin takes part in breathing, and the internal structure of the frog allows you to breathe with the help of the lungs, which have a network of blood vessels.

The frog opens its nostrils, the bottom of the oropharyngeal cavity descends and air enters it. Then the nostrils close, and the bottom rises, and air enters the lungs. With the collapse of the lung walls and the contraction of the abdominal muscles, exhalation is carried out.

Digestive system

It begins with a rather large oropharyngeal cavity. At the sight of prey, the frog throws out its tongue and the victim sticks to it. Small teeth are located on the upper jaw and serve to hold prey. The structure and activity of the internal organs of the frog contribute to the processing of food. It is wetted by the secretion of the salivary glands in the oropharyngeal cavity and enters the esophagus, and then into the stomach. Incompletely digested food enters the duodenum and then into small intestine where nutrients are absorbed. Undigested residues go out through the cloaca, having previously passed through the rectum (hind) intestine.

excretory system

On the sides of the sacral vertebrae are two kidneys that contain glomeruli and perform filtration of decay products and some nutrients from the blood.

The latter are absorbed in the renal tubules. Urine enters the bladder after passing through the ureters and cloaca. The internal structure of the frog allows the muscles Bladder shrink when filled. Urine enters the cloaca and then exits.

Metabolism

It flows rather slowly. The body temperature of the frog also depends on the ambient temperature. It decreases in cold weather and rises in warm weather. In extreme heat, due to the evaporation of moisture from the skin, the body temperature of the animal decreases. Due to the fact that these are cold-blooded animals, when cold weather sets in, they become inactive, choosing warmer places. And in winter, they completely hibernate.

sense organs

The structure and functions of the frog's internal organs help it adapt to living conditions:

The frog is able to blink, having a movable upper eyelid and the so-called nictitating membrane. It wets the surface of the eye and removes dirt particles adhering to it. The animal reacts more to a moving object, and a stationary one does not see well enough.
The hearing aid consists of the inner and middle ear. The latter is a cavity that opens on one side into the oropharynx, and on the other side goes to the surface of the head, separated from the external environment by the tympanic membrane, which is connected to the inner ear with the help of a stirrup. Through it, sound vibrations are transmitted to the inner ear from the eardrum.
The animal is quite well oriented by smell. The olfactory organs communicate with the external environment through the nostrils.

Conclusion

Thus, the features of the internal structure of the frog, like other amphibians, are in a more complex structure of the nervous system, as well as the sense organs. In addition, they have lungs and two circles of blood circulation.

Answers in zoology from 31-60. 1 course BHF.

Question

general characteristics and taxonomy of the subclass Arcuvertebral amphibians.

Amphibians, or amphibians, are the first terrestrial vertebrates that still retain significant connections with the aquatic environment. In most species, eggs (caviar) are devoid of dense shells and can only develop in water. Each egg is surrounded by a transparent mucous membrane that swells in water. Embryos do not have embryonic membranes (anamnia). The larvae hatched from the eggs lead an aquatic lifestyle and only then undergo metamorphosis (transformation), during which the characteristics of adults leading a terrestrial lifestyle are formed.

Adult amphibians are characterized by paired limbs with articulated joints. The skull is movably articulated with the cervical vertebra by two occipital condyles. The pelvic girdle is attached to the transverse processes of the sacral vertebrae. Two circles of blood circulation are formed, not completely separated: in the heart there are two atria, but one ventricle. The eyes have movable eyelids. The lateral line organs usually disappear in adults. The forebrain is enlarged and divided into two hemispheres; there are accumulations in its roof nerve cells. The average metabolic rate of amphibians is noticeably higher than that of fish. Along with this, amphibians also retained signs of aquatic vertebrates.

Appearance 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.

Nervous system amphibian has undergone significant complications compared with 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.

sense organs amphibians have received progressive development in the process of evolution. nasal cavity communicates with the mouth through the internal nostrils - choanae. Due to the fact that the air environment is less sound-conducting, the structure of the inner ear has become more complicated in the hearing organs of amphibians and the middle ear has formed ( tympanic cavity) with auditory ossicle. The middle ear is bounded externally by the tympanic membrane. It communicates with the throat canal (Eustachian tube), which allows you to balance the air pressure in it with the pressure of the external environment.

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 language 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 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 a relatively short intestine, which is divided into thin and thick sections.

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. Mature eggs exit into the body cavity, from where they enter the funnel-shaped initial departments oviducts. Passing through the oviducts, the eggs are covered with a transparent thick mucous membrane.

feed on amphibians are 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.

Question

The external structure of the frog as a representative of the amphibian class. The structure of the limbs.

feed on frogs eat various insects, mainly beetles and Diptera, but also eat spiders, terrestrial gastropods, and sometimes fish fry. Frogs lie in wait for their prey, sitting motionless in a secluded place.

When hunting, sight plays a major role. Noticing any insect or other small animal, the frog throws out a wide sticky tongue from its mouth, to which the victim sticks. Frogs grab only moving prey.

The external structure of the frog

Two large bulging eyes are visible on the head, protected by eyelids: leathery - upper and transparent movable - lower. The frog blinks frequently, while the moist skin of the eyelids wets the surface of the eyes, protecting them from drying out.

A pair of nostrils is visible in front of the eyes on the head. These are not only the openings of the olfactory organs. The frog breathes atmospheric air, which enters its body through the nostrils. The eyes and nostrils are located on the upper side of the head. When the frog hides in the water, it exposes them to the outside. At the same time, she can breathe atmospheric air and see what is happening outside the water. Behind each eye on the frog's head is a small circle covered with skin. This is the outer part of the organ of hearing - the tympanic membrane. The inner ear of the frog, like that of fish, is located in the bones of the skull.

The frog has well-developed paired limbs - front and hind legs. Each limb consists of three main sections. In the front leg, there are: shoulder, forearm and hand. In a frog, the brush ends with four fingers (the fifth finger is underdeveloped in it). The skin of all modern amphibians is naked. In a frog, it is always moist due to the liquid mucous secretions of the skin glands.

Water from the environment (from reservoirs, rain or dew) enters the body of the frog through the skin and with food. The frog never drinks.

Unlike fish, frogs have a cervical vertebrae. It is movably articulated with the skull. It is followed by trunk vertebrae with lateral processes (the frog's ribs are not developed). The cervical and trunk vertebrae have superior arches that protect the spinal cord. A long tail bone is placed at the end of the spine in a frog and in all other anurans. In newts and other tailed amphibians, this section of the spine consists of a large number of movably articulated vertebrae.

The frog skull has fewer bones than the fish skull. In connection with pulmonary respiration, the frog does not have gills.

The skeleton of the limbs corresponds to their division into three sections and is connected to the spine through the bones of the limb belts. The belt of the forelimbs - the sternum, two crow bones, two collarbones and two shoulder blades - has the form of an arc and is located in the thickness of the muscles. The hind limb girdle is formed by fused pelvic bones and is attached tightly to the spine. It serves as a support for the hind limbs.

Question

Features of the internal structure of the frog as a representative of the class of amphibians.