Modern reptiles known about 6 thousand species.

They are mostly terrestrial. Most of them live in latitudes with tropical and subtropical climates. Some also penetrate the northern regions.

Reptiles belong to the group of higher vertebrates with internal fertilization. With the development of the embryo are formed germinal membranes. In addition, reptile eggs have dense egg shells, which in combination with the first provide the possibility of the development of the embryo in air. However, the blood in the trunk arteries mixed. The capacity for thermoregulation is low, so the temperature of the body is not constant: for some lizards, for example, it ranges from 14 to 32 ° C.

The shape of the body of reptiles is diverse. Their size ranges from a few centimeters to 12 m or more. The color is often patronizing: from light gray and sandy to black, usually with a pattern of stripes and spots.

The body of reptiles is clearly subdivided into head, neck, torso  and tail. Head slightly flattened from above and pointed in front. On the head is large mouth  and on the sides of the head eyes  with lower  and upper eyelids. In addition to them in the front corner of the eye is visible nictitating membrane. External nostrils  open at the sides of the end of the muzzle. Large dormer holestightened eardrum, are located on the sides of the back of the head.

The head is connected to a short, but rather mobile neck, which passes into an elongated body, mobile thanks to the flexibility of the spine and the development of the muscular system. The extremities of the lizards are located on the sides of the body. The humerus and femur are parallel to the surface of the earth, so the body sags and touches the surface of the earth. Fingers are armed with sharp horny claws.

The body gradually turns into a long tail, tapering towards the end. At the transition of the trunk to the tail from the ventral side there is a transverse vent hole. Many species have a large cloacal plate in front of the cloaca.

The covers of the body.   The skin of reptiles consists of epidermis  and derma, unlike amphibian skin, dry  poor in glands, which some turtles, apparently, do not exist at all.

The lizards on the inner edge of the thighs can see a series of holes - femoral pores, more developed in males. Their appointment is not entirely clear. The epidermis is horny, so the reptile's body is covered with scales and shields of various sizes and shapes. Small rounded and rhombic scales are found on the neck and back. On the sides of the body, larger scales are arranged in longitudinal rows, on the belly there are scutes. On the tail, the scales are arranged so that they give the covers a ringed appearance.

Keratinization of integuments is important adaptive in connection with life on land, protecting the body from draining and protecting it from mechanical damage. In species living in arid desert areas, evaporation of moisture is very insignificant, but in crocodiles living in water, up to 75% of all moisture loss occurs through the skin.

The skeleton of reptiles.   In the skeleton stand out skull   and spine . A common feature of the skull is the almost complete ossification of the primary cartilage skull and the development of a large number of skin bones that form the roof, sides and bottom of the skull. The skull has an elongated shape and an increased volume of the brain. The spinal column consists of 4 departments (in some directories 5 departments): cervical, lumbar-thoracic, sacral  and caudal.

In the cervical lizards there are 8 vertebrae, and the first two have a peculiar structure. The first cervical vertebra, called atlanta , is a ring, divided into a bunch on the upper and lower halves. The upper opening serves to connect the brain with the spinal cord, the denticular process of the second cervical vertebra enters the lower half-ring - epistrophy.   Atlas around him rotates.

The lumbar-thoracic lizards comprise 22 vertebrae. They all carry ribsbut only from the first 5 vertebrae the ribs join sternum  and form the real chest,  common to most reptiles. However, some reptiles, such as snakes, have no chest. The sacral region consists of 2 vertebrae, to the transverse processes of which the bones of the pelvis are attached.

In the caudal region several dozen vertebrae. The bodies of almost all caudal vertebrae are divided by a thin non-stiffening layer into anterior and posterior sections. When breaking off the tail ( self-healing , or autotomy) Due to contractions of the muscles of the tail, the gap does not occur between the two vertebrae, but in the middle of one of them, in the region of the neostosten layer.

Shoulder girdle  reptiles presented karacoid, spatula , suprascapular cartilage and collarbone . Karakoid is connected with the sternum, which provides greater strength of the shoulder girdle. This feature reflects a greater adaptability to life on land than amphibians.

Pelvic girdle  Reptiles are much stronger than amphibians. The skeleton of the fore and hind limbs has a typical vertebrate structure. Forelimb: shoulder, forearm (ulnar and radius), hand. Hind limb: thigh, shin (large and small shin bones), foot.

Musculature . The strong dissection of the body of reptiles leads to a complex differentiation of the muscular system. Manifests itself intercostal muscles which plays an important role in the mechanism of respiration, the abdominal muscles, neck, subcutaneous, flexors and extensors of the fingers.

Digestive system.   The digestive organs in reptiles are differentiated more strongly than in amphibians. Oral cavity   reptiles are markedly delimited from throats . At the bottom of the mouth is movable muscular. tongue,   able to throw away far. The shape of the language in different species is not the same. In snakes and many lizards it is thin, often forked at the end, in chameleons it is expanded. The shape of the tongue is related to the nature of the food and the method of its production.

Teeth  peculiar to most reptiles. They sit on the upper and lower jaws. They are of the same type, conical shape (homodont dental system). The teeth are used to capture, hold, tear and kill prey. The teeth grow to the edges of the bones, only in crocodiles they sit in the alveoli. Salivary glands   more developed than amphibians. The secret of the salivary glands contains not only liquid for wetting food, but also enzymes (amylase, etc.), and some snakes and lizards are poisonous (as some snakes and lizards have poisonous glands). Followed by throat, esophagus . Distinct muscular stomach.   The intestine is divided into a long thin   (the initial section of the small intestine - duodenum ) and relatively short large intestine . On the border of their separation, a rudimentary cecum which only herbivorous tortoises  well developed. Ducts the liver (liver with gall bladder ) and pancreas   open to the initial section of the small intestine. Ends intestine straight flowing into cloaca .

Respiratory system.   Reptiles breathe only light . Skin respiration is absent due to the appearance of horny cover. Respiratory tract begin nasal cavity having external respiratory openings (nostrils ) and internal respiratory openings (choanas) opening into the oral cavity. Followed by larynx   and trachea whose back end forks into two bronchus included in lungs . The walls of the trachea and bronchi contain cartilaginous rings .

The lungs have a bag-like shape, but the complex partition system  (increase the area of ​​gas exchange), forming, for example, in lizards and snakes, a multitude of small cells (small-mesh form). The cells of higher reptiles - turtles and crocodiles (spongy form) are especially strongly developed. The back of the lungs in many species, such as lizards and chameleons, does not have cells and partitions, it is often elongated and has the shape of thin-walled finger-like outgrowths - pulmonary bags .

Breathing is due to the expansion or reduction of the volume of the chest in connection with the movement of the ribs and contraction of the intercostal muscles. The air is sucked into the lungs and pushed out of them through the trachea, which branches into two bronchi. The frequency of ventilation varies depending on the ambient temperature. In lizards, when the air temperature is 15 0 С, the respiratory rate is 26 respiratory movements per 1 minute, at 25 0 С - 31, and at 35 0 С - 37.

Circulatory system.   Reptilian circulatory organs correspond to terrestrial lifestyle and the associated pulmonary respiration. This is reflected in a more complete separation of arterial and venous flows, due to the emergence of new devices in the heart and arterial system.

The heart of most reptiles three-chamber however the septum in the ventricle incomplete. In crocodiles, this septum is full and the heart has two independent ventricles. The arterial cone is reduced. In the arterial system of reptiles, there are three vessels that independently extend from different parts of the ventricle. From the right side of the ventricle, the pulmonary artery leaves the venous blood to the lungs, and the oxidized blood returns to the left atrium through the pulmonary veins. From the left side of the ventricle, the right aortic arch departs, which carries arterial blood to the head and forelimbs, and the left aortic arch, to which mixed blood flows, departs from the middle part of the ventricle. Having rounded the heart, both aortic arches merge into the dorsal aorta, which supplies the trunk, internal organs and hind limbs with mixed blood. According to the hollow vein system, venous blood returns to the right atrium.

Reptiles cold-blooded (poikilothermic ) animals, as their body temperature is not constant. Their metabolism is slow, but if we compare them with amphibians, the body temperature of reptiles is higher than that of amphibians. An important role in this is played by adaptive behavior - reptiles love to bask in the sun. Most of the species inhabit areas with a warm climate, only a few species in the Northern Hemisphere reach the Arctic Circle. Maintaining body temperature also helps chemical thermoregulation. High concentration of sugar in the blood allows you to enhance heat generation when the body is cooled. In temperate and northern latitudes, reptiles spend the winter in a deep stupor, hiding in various shelters.

Nervous system   reptiles are more developed than amphibians. Brain   represented by 5 departments: front, intermediate, middle, back (cerebellum) and oblong. The cerebral hemispheres are larger than those of amphibians and have rudiments bark (secondary cerebral vault - neopallium) from the gray brain matter in the form of three islets. Well developed parietal organ, epiphysis   and cerebellum . The cerebellum is large and complex, so reptiles have a variety of movements. The medulla oblongata forms a bend in the vertical plane, which is characteristic of higher vertebrates.

The organs of sense of reptiles correspond to the terrestrial way of life. Mechanical irritations are perceived by the so-called tactile hairs located on scales. The olfactory organs are differentiated into a number of departments. In addition, reptiles have a so-called jacobson organ   - a tortuous and blindly ending cavity extending from the roof of the mouth. It is believed that this formation serves to perceive the smells of food already in the mouth. In addition, many reptiles, such as lizards, groping various objects with the help of a far-advanced language.   By drawing the tongue into the oral cavity, they carry the smallest particles of objects into the mouth, where their smells are perceived by the Jacobson organ.

Each eye   supplied upper   and lower moving eyelids.   The lower eyelid is developed stronger and more mobile. There is also a third eyelid - nictitating membrane covering the eye from its front angle. In snakes, the upper and lower eyelids are adherent and transparent. Lacrimal gland   protects the eyes from drying out by wetting the surface of the eyeballs. Focusing on the sharpness ( accommodation ) is carried out by a special ciliary muscle, which not only moves lens , but also changes its shape. Many daytime people have color vision. Some representatives hunting at night have parietal eye perceiving infrared radiation.

The organ of hearing - inner   and middle ear   with one auditory bone (stapes ) and eardrum . The eardrum lies below the surface of the skin, and thus, the majority of reptiles have a rather clear leathery rim bordering the ear openings, - rudiment of the outer ear.

Sense of smell - nasal receptors.

Some snakes on the flaps of the upper and lower jaws have pits , able to perceive the thermal (infrared) radiation produced by animals. Perhaps these organs are able to distinguish between temperatures of 0.001 0 C.

Excretory system . Bodies of allocation of adult reptiles are presented secondary (pelvic) kidneys. Depart from them ureters,   Further cloaca,   then bladder which in turn opens into a foul place. The kidneys provide active reabsorption of water from the primary urine and producing concentrated urine. Exchange product - uric acid   in the form of a suspension of small crystals (mushy) - "white urine". It is practically insoluble in water and can be excreted without much loss of moisture.

Reproduction.   Fertilization in reptiles is internal. The sex glands of reptiles lie in the body cavity on the sides of the spine. Male genitals - paired testes   - have a rounded shape. They are connected to seed tubes (wolf channels ), opening into the ureters near the place of their confluence into the cloaca. Through the channel system, the sexual products enter the cloaca. In males of different species, the aggregate organ is differently arranged (growth of the walls of the cloaca). The female reproductive system is represented by two ovaries   and oviducts (Muller channels) . Egg farmers begin funnelsbefore flowing into the cloaca, the oviducts expand to form "Uterus". In pregnant females, the "uterus" is greatly expanded and stretched by the eggs in them. Near the kidneys are paired fat bodies   peculiar blade shape. Fertilization of eggs occurs in the upper part of the oviducts. The resulting zygote moves through the oviduct, is covered in its middle part. protein coat and at the bottom shell .

In comparison with amphibians, reptiles have larger eggs. Enlargement of eggs comes from enriching them with yolk. A large supply of nutrients in the egg causes the possibility of direct (without transformation) development. In reptile eggs, a series of shells appears, appearing both at the expense of the embryo itself ( amnion, serosa and allantois ) and the membranes produced by the relevant divisions of the oviducts (fibrous, lime and protein coat) . In the early stages of development, the embryo sinks into yolk.   From the head of the embryo there is an outgrowth, which expands and forms a closed bag. (amnion).   Its cavity is filled with fluid. Allantois   arises as a saccular outgrowth of the posterior intestine. It grows, takes on the appearance of a large bubble and surrounds amnion . Allantois serves two functions: the respiratory organ and the germinal bladder. On top of it covers the serous membrane. The fibrous casing covers the eggs of all reptiles. It protects them from spreading, mechanical damage, drying, from the penetration of bacteria. In some (for example, turtles, crocodiles) the yolk is surrounded by a protein coat and even the shell develops.

Nutrients are contained in the yolk, water - in the liquid protein layer of the egg. Gas exchange is carried out through the serous germinal coat.

Reptiles reproduce by egg laying  in the pits on well-warmed places. It is peculiar to some species. ovidbirth,  in which the fertilized eggs remain in the genital tract of the female and pass through all stages of development, and the young hatch from the eggs immediately after their laying. Few have live birth,  wherein the embryo develops in the mother's body due to its nutrients. The development of reptiles is direct.

The class of reptiles includes several squads.

Scale squad

Scaly reptiles known more than 5.5 thousand species. They include lizards, chameleons and snakes. The structure and appearance of their very diverse. However, common features are characteristic of all members of the detachment: the body is covered with horny scales of various size and shape, the teeth are sprung to the jaws, the cesspool in the form of a transverse slit. In the detachment 3 suborder.

Suborder Lizards. The total number of lizard species reaches 2.5 thousand. Most of them have a moderately elongated body with a clearly defined neck and a long moving tail. A significant number of species of limbs are well developed, but their shape varies. Few members of the detachment of the legs do not have at all or they are underdeveloped. By appearance  such lizards look like snakes, but most of them have limb girdles. The bones of the upper jaw are still attached to the skull. The left and right halves of the lower jaw are spliced. Usually there are mobile eyelids and visible eardrum outside. Many species have the ability to break off part of the tail ( autotomy,  or self-healing). After a break, the tail is restored, but its skeleton does not ossify.

Lizards are very common. In the mountains, certain species rise to an altitude of up to 4000 m. Some lead a semi-timber lifestyle. In water, there are few forms.

Real lizards - small and medium in size, slender animals. The five-toed limbs are well developed, the tail is brittle. The greatest number of species inhabit the steppes, deserts and foothills. In the forest belt, they prefer areas with dry, well-heated soil. The only exception is the viviparous lizard, common in shaded forests, often on moist mossy soil. This is the only lizard species that crosses the polar circle.

Is common quick, or agile lizard. Lives in mink. From them departs no further than 15-20 m. For the winter, it hibernates. Able to tolerate cooling to -5-7 ° C. When the air and soil warms up, the lizard returns to active life. In the spring, it lays eggs in dry, well-warmed places (in the sand. Moss, under fallen leaves). Since the end of July and almost the whole of August, small lizards, capable of independent existence, have come out of the eggs. The basis of food sand lizard  make up various insects and slugs. During the day, one individual can kill up to 70 invertebrates, among which there are quite a few pests with commercial crops. Therefore, lizards are useful animals. Close to fasting, but bigger green lizard.

Swindles  form many transitions from forms with developed limbs to legless, outwardly similar to snakes. In our country, there are 2 legless species: common spindle, or sucker  (yellow), up to 26 cm long, and yellow Pet. Swindle breeds live birth. Yellowtopuzik is olive-yellow, up to 1 m long. It reproduces by laying eggs.

Varans- large. Up to 3.5 m long, slender lizards with a very long moving tail and well-developed legs, run quickly, lifting the body high above the ground. Gray monitor lizard, up to 60 cm long, has yellowish-gray coloring with brown cross strips. It lives in sandy deserts. It feeds on arthropods, rodents, eggs of turtles and birds. The largest, up to 3, 65 m long, the monitor lizard was discovered in 1914. He lives on the islands of Komodo and Flores (Indonesia). It feeds on small mammals and birds. Often eats wild pigs killed by hunters.

flying Dragon  interesting adaptation to planning a flight. Distributed in the forests of South Asia. Jumping from tree to tree, flies up to 20 m.

Iguana - large lizards up to 1.5 m long. Distributed almost exclusively in the Western Hemisphere. They live in mountains, forests, deserts, and some species live in water, sometimes even in the sea. They breed by laying eggs and egg production. Eggs and iguanas are used by the local population for food.

Suborder Chameleons. Chameleons are close to lizards but highly organized reptiles that adapt mainly to life in the trees. Most of them have a body length of 25-35 cm, in the largest ones up to 50, rarely up to 60 cm, and in the smallest - no more than 5 cm. The body of the chameleon is compressed from the sides, there is a sharp keel on the back. Legs long, adapted to the lasagna. Fingers grow together in two opposite groups and resemble claws that can tightly clasp the branches of trees. The tail is long, tenacious, used for climbing. Peculiar organs of vision. The eyelids are thick, convex, covered with small scales and a small hole for the pupil. The movements of the left and right eyes can be made inconsistently, which is of great importance when catching insects: the width of the visual field increases. The body of chameleons can swell a lot, which is associated with filling the air bags of the lungs.

  The variability in the color of chameleons, caused by the movement of skin pigments under the influence of a number of conditions (eg, light, temperature, fright), is well known. In catching the chameleon with great speed throws out a long tongue, the thickened end of which looks like a cylinder cut in front. When hunting, chameleons usually sit for hours motionless on the branches of trees, looking for flying and crawling insects. At that time, the chameleon’s body remains stationary, its eyes constantly moving. Sometimes chameleons sneak up on prey quickly.

Suborder snake. It has about 2300-2500 species of snakes. They are widespread everywhere, but numerically prevail in warm latitudes. They live in deserts, steppes and mountains. Most live on land, but some may live in trees, in soil, in water.

Snakes have a long body, weakly subdivided into the head, neck, torso and tail. There are practically no paired limbs and their belts. There are also no mobile eyelids and eardrum.

The body is covered with horny scales and shields, which are periodically updated. Shedding proceeds in a peculiar way. The old surface layer of the skin is separated on the jaws and gradually comes down from the body, twisting like finger gloves. When moulting and the superficial layer of the conjoined eyelids, so the eyes of snakes after molting are most transparent.

The structure of the skull has a number of features that ensure the ingestion of large prey. The bones of both jaws and palate are connected by bundles, so the mouth can open wide. Swallowing food is achieved by alternating movements of the left and right half of the lower jaw. The snake crawls on its prey. The passage of a large food bolus along the anterior digestive system is facilitated by the production of salivary glands. Most snakes are not poisonous. They kill the prey by the mechanical action of the teeth or body that is wrapped around the victim. Poisonous snakes have several large front teeth, they have channels or grooves through which the poison flows.

Due to the elongated shape of the body and the winding pattern of movement, the spine is represented by a large number (140-435) of monotonous vertebrae.

Only the right lung is developed, and the left one, if there is, then is rudimentary. Kidneys strongly elongated, no bladder. They reproduce by laying eggs, egg production and live birth.

Snakes eat animal food of various sizes - from small insects and rodents to deer. They catch the prey and rush at it with lightning speed. Venomous snakes attack humans only when disturbed.

Boas  there are both small, up to 1 m long, and large - up to 10 m. They have rudimentary hind limbs. Coloring is usually variegated.

Almost all boas are common in tropical areas. Only a few species are found in the steppes and deserts. Boas live in thickets and in marshes. Usually active at night. In the dense forests, where twilight is set during the day, they hunt during daylight hours. To the prey creep slowly and cautiously, catch it, rushing from a short distance. They stifle prey, wrapping themselves around the victim in several turns.

Best known reticulated python  length from 5-6 to 10 m. Common boa  reaches 5-6 m. The smallest representative - steppe boaup to 1 m. he is nocturnal. During the day, it sits in rodent burrows or buries itself in sand, under the surface layer of which it can move. It catches jerboa, gerbil, and small reptiles.

Edible  - the largest group of snakes. They are more than 1000 species. Poisonous, already-shaped teeth do not have a channel, their poison flows down a groove on the front surface of the tooth.

Ordinary too differs from other species by the presence of two yellow symmetrically located spots behind the temples on an almost dark head. He lives on the banks of rivers, swamps, ponds. It feeds on frogs, lizards, rodents, occasionally insects. Fish is rare. They reproduce by laying eggs, which they place in rotting plant rags in damp places.

Close to uzham snakes  up to 2 m long. They have no poisonous teeth, but the pursued ones can throw themselves at a person and bite.

Medyanka  - it is a non-poisonous small reddish-brown snake up to 75 cm long. It occurs in shrubs or in the forest. Raw places avoids. It feeds mainly on lizards. In the deserts are numerous arrow snake. It has a thin, up to 1 m long, yellowish-gray, with longitudinal rows of spots. When pursuing this snake quickly crawls away, hiding in the branches of the bushes, which deftly climbs. It is poisonous. Kills prey, twisting and squeezing her body or biting.

TO aspidinclude poisonous cobra snakes. They have the ability to expand the neck, which is associated with the mobility of the edges of the cervical vertebrae. Cobra threatening pose taken in the excited state. Gray cobradwelling in the gorges and near human dwellings. Its bite is very dangerous.

Aspid close sea ​​snakes. They live in tropical seas. The tail of these snakes is wide, leaf-like. Most species are viviparous. All poisonous. The poison is very toxic, but is administered in small doses.

Vipers  - These are poisonous snakes with the most advanced poisonous apparatus. Their poisonous teeth are perforated by channels. The upper jaws are short, and when opening the mouth, the poisonous teeth are directed forward.

Common Viper  usually lives in the forest, avoids marshes. In the afternoon, vipers often sit on stumps, piles of brushwood. They hunt at night, catching mice, voles, birds, lizards, frogs, insects. Reproduced by egg production. In the winter they gather in underground shelters, where they accumulate in large numbers. Viper bite is especially dangerous for the weak, sick people and for children.

Gyurza  - up to 2m. Very poisonous. Besides this snake is also very poisonous. sand effect  and shtekomordnik.

Order Crocodiles

The most highly organized reptiles - crocodiles has 25 species. Their body is elongated, flattened. The tail is compressed from the sides and serves for swimming. There are 5 free toes on the front paws, and 4 toes on the hind paws connected by a membrane. Crocodile teeth sit in grooves - alveoli. The ventricle of the heart is divided by a septum into 2 isolated halves, thus the heart of crocodiles four-chamber.  Well known gavialy up to 6 m, nile crocodiles  - up to 8 m (sometimes up to 10 m), chinese alligators  - up to 2 m.

Crocodiles live in water, prefer slow flowing rivers, lakes. On land rarely go. Crocodiles breed by laying eggs the size of a goose into holes dug on the coastal sand. In clutch there are several dozen eggs. The incubation period lasts 1.5-2 months.

Crocodiles feed on a variety of animal food: from mollusks to relatively large mammals. Can attack people. Prey caught in the water, slowly sneaking up to her. The mouth is open and the whole body is immersed in water.

When hunting, guided using hearing and vision. In water, crocodiles are agile and agile, clumsy and slow on land. Mostly they are mined using meat and valuable skin, or bred on special farms.

Turtle Troop

Turtles are known about 210 species. Their main adaptation to passive protection is the development shell,  which encloses the torso and can retract the neck, head, limbs and tail. The shell develops from the bone formations of the skin, as well as through the strong expansion and coalescence of a number of skeletal bones. Upper part of it ( carapax) grows together with ribs and spine, except for the cervical and caudal divisions, lower ( plastron) - with the sternum and collarbone.

In some turtles, poorly developed bone shell is covered with soft, wrinkled skin. In sea turtles, limbs are transformed into flippers.

The turtles have no teeth. A peculiar mechanism of respiration. The role of the pump is performed by the oral cavity, the bottom of which rises and falls. The air is sucked through the nostrils into the oral cavity, and from there it is pushed into the lungs.

The marsh turtle lives in the steppe belt, where it inhabits stagnant or slow-flowing water bodies. For the rest goes to the bumps, at risk hiding in the water. Winter spends in hibernation. Eggs are laid in the sand of coastal waters.

In the deserts and low mountains there is a steppe tortoise. The armor is in females up to 25 cm long, the males are noticeably smaller. Winter falls into hibernation.  They lay eggs from which little turtles come out in 70-80 days. By the way, they can fall into summer hibernation. Most individuals summer hibernation goes into winter. As a result, the turtles sleep 7-8 months.

In the fresh waters of the Far East lives soft-skinned Ussuri turtle.  Her legs are equipped swimming membranes. There is a long movable proboscis, at the end of which the nostrils open. Swims quickly and can swim several kilometers. Under water can stay 2-10 hours. The turtle goes to the shore to breed and bask in the sun. When danger on land can burrow into the sand. Wintering goes under water. If you carelessly handle these turtles, they may bite painfully.

Most species of turtles live in tropical countries. On the islands of the Indian and Pacific Oceans found ivory turtle, up to 2 m long, and weighing up to 200 kg. Even bigger - soup,  or green turtle, common in the seas of the tropical belt, more than 1 m long, weighing up to 450 kg.

Caretta- a tortoise with a beautiful shell, which is extracted for making jewelry.

Goals:

1. Determine what is gas exchange?
2. Determine how respiratory organs change with habitat change?

The evolution of the respiratory organs of terrestrial vertebrates

Mastering the land was associated with the transition to breathing air oxygen. Water breathing organs - the gills - in terrestrial vertebrates, in adulthood, are usually atrophied. However, the lower terrestrial vertebrates — amphibians — still retained many of the important features of the respiratory system characteristic of their fish-like ancestors. (The modern amphibians living in the water of the larvae have external gills).
  Morphologically, the lungs amphibians are arranged,  in essence, quite similar to the lungs of lungfish. It is paired bag-shaped organs  opening in a common laryngeal-tracheal chambers. In turn, the laryngeal-tracheal chamber opens with a laryngeal slit in the back of the bottom of the oropharyngeal cavity. The inner surface of the lungs in some amphibian species is almost smooth, in others - cellular (there are partitions of the first, second and third order, protruding from the walls of the lung into its cavity and significantly increasing the surface of gas exchange). In the walls of the lungs, as in lungfish, there are smooth muscle fibers.
For ventilation of the respiratory system, amphibians use not the mouth opening, as fish, but short nasal passages, opening with external nostrils to the external environment, but internal nostrils, or choans- in front of the roof of the oral cavity. Most fish have two pairs of external nostrils, which serve to exchange water in the organ of smell. In lungfish and cross-finch fishes, the posterior pair of these openings has moved into the oral cavity and became choanas, but their nasal passages are also used only for the maintenance of the olfactory organ. In amphibians, these passages receive an additional function of the respiratory canals.
  The need to ensure the respiratory function of the skin caused a chain of morphophysiological restrictions and prohibitions, which largely determined many of the features of the organization and the adaptive capabilities of amphibians. To ensure skin breathing, the skin must be devoid of protective formations (such as scales, etc.).
  The role of the skin in the general gas exchange is relatively higher in amphibians with long and narrow body  (tritons, salamanders, worms), in which the work of the injection pump of the sublingual apparatus for ventilation of long and narrow lungs is particularly ineffective. In such species, skin respiration significantly predominates over pulmonary. Some tailed amphibians have completely lost their lungs and have completely switched to skin respiration (a family of pulmonary salamanders, living mainly in America). In tailless amphibians, pulmonary respiration prevails.
In reptiles, birds and mammals, changes in the volume of the chest part of the body cavity, where the lungs are located, through the movements of the ribs caused by contraction of the muscles of the body wall, became the respiratory mechanism. This method of ventilation, which provides changes in the volume of the lungs themselves and according to the principle of action, corresponds to the suction (diluting) pump, much more efficiently than the pressure pump of the sublingual apparatus. The common for all of them was the formation of the chest - the skeletal complex, which includes the thoracic vertebrae, the ribs (often divided into two moving parts) and the sternum. Contraction of different muscle groups changes the position of the sternum and ribs, compressing and straightening the chest.
It became possible to completely separate arterial and venous blood in the ventricle of the heart, which opened the way to the development of mechanisms to maintain a constant body temperature, independent of the ambient temperature reached in birds and mammals.
In snakes, with their long and narrow body, only one (right) lung is preserved.
  Ventilation of this lung with its considerable length is difficult. This problem was solved in snakes by developing a so-called air sac, which is a thin-walled vesicular organ that extends slightly posteriorly. The walls of the respiratory bag are devoid of respiratory tissue, and gas exchange with blood in this organ does not occur. Due to the presence of the air bag in a light kite there is no stagnant air - it remains in the air bag, mixing with fresh portions of air with each breath. And the lung, therefore, is a through organ, through which air is pumped in while inhaling and exhaling in different directions. Due to the fact that snakes are crawling, relying on the ends of their ribs, the usual mechanism for amniot movements of the chest they can not function. Changes in the volume of the body cavity in snakes occur through movements of the middle part of the belly, to which special muscles are attached, starting from the inside of the ribs. Their contraction somewhat draws the abdominal wall of the body inward.
Fitness for flight  identified key features  organizations of birds, in particular the characteristics of their respiratory system. Flight requires a significant increase in the level of metabolic processes and, consequently, the intensification of gas exchange. This intensification was achieved in birds by an extremely high degree of differentiation of the lungs and respiratory tract and the formation of a special mechanism of ventilation of the lungs.
With all the complexity and high perfection of the respiratory organs of birds, it is quite obvious that their organization has developed as a further development of the tendencies of differentiation of the respiratory tract and chamber lung, already planned in reptiles.
Mammals lungs,  formed by a combination of alveoli and branching bronchi, usually do not form compact sacculate organs, but rather are separated by rather deep cuts into large lobes (the number of which is different for different groups of mammals).
  The mechanism of ventilation of the lungs in mammals is in principle similar to that of other amniotes. This is a suction (dilution) pump, whose work is based on changes in the volume of the chest cavity. The latter in mammals is separated from the abdominal cavity by a pectoral barrier - the diaphragm.
Respiratory organs of mammals and birds  provide such an intensity of gas exchange, which is sufficient to achieve a high level of metabolism, allowing the occurrence of warm-bloodedness. It should be noted that, in general, the intensity of gas exchange in the lungs of birds is higher than that in the lungs of mammals. This is ensured by the high efficiency of the ventilation mechanism of birds in birds and the enormous surface of gas exchange; when comparing animals with the same body weight, it turns out that the surface of the bird's respiratory capillaries is about 10 times larger than the surface of the pulmonary alveoli of the mammal.
Evolutionary transformations of the organs of the respiratory system often act as aromorphoses. In the evolution of terrestrial vertebrates, the undoubted aromorphoses were: