Many non-venomous snakes hiss, raise the front of the body, or open the same hood as a cobra, trying in every possible way to impress the enemy that they are not safe to deal with. And it often works. This resemblance of an unprotected organism to a well-protected one is called mimicry. It is curious that even some lizards have learned to imitate poisonous snakes. For example, the common scalefoot, widespread in South Australia. This long-bodied snake-like lizard with barely visible legs raises its head high in danger, arches its neck and, inflating its throat, hisses loudly, like a snake.

A remarkable example of mimicry is known from the South African foot-and-mouth disease. The weak and defenseless cubs of these lizards are completely different in color from their own parents, but look like ... beetles - poisonous ground beetles living next to them. In terms of body size and shape, small lizards are really close to beetles, and so that their tail does not give out, it is painted in the color of the ground and is almost invisible.

Aggressive reptiles

As a rule, reptiles do not look for enemies and do not seek to attack first. They use their "weapons" only for the purpose of forced defense. But differences in temperament also play a role. And among the reptiles, some are particularly vicious and aggressive (of course, from our, human point of view). For example, found in the south of our country yellow-bellied snake has a particularly bad temper. When someone says that a snake was chasing him, then, if this is not fiction, it is most likely about this snake. Of course, the snake does not rush at people on purpose. But if a person threatens him, this snake, reaching two meters in length, often rushes into the attack itself - with a loud hiss and wide-open mouth. At the same time, she can "jump" towards the enemy at a distance of up to one meter, trying to cling to the very vulnerable spot, often causing severe bites. Aggressiveness is distinguished not only by adult snakes, but also by their juveniles.

yellow-bellied snake

Species characterized by particular aggressiveness are not only among different groups snakes, but also among water turtles, crocodiles, monitor lizards.

procreation

For life to end...

The main task of any organism is to leave behind offspring. Reptiles solve this problem in many ways fundamentally differently than amphibians. As fully terrestrial animals, they only reproduce on land, laying eggs or bearing live young.

Reptile eggs are much larger than those of amphibians, and are protected by dense multi-layered shells, the main task which - to protect the embryos from drying out. Therefore, amphibian clutches can develop only in water or in very wet places, and reptiles can lay their eggs on land, even in completely dry sand. In crocodiles, many species of turtles and lizards, the eggs are covered with a hard calcareous shell - a shell (like in birds). In other reptiles, the shell is leathery, elastic.

Reptile eggs are rich in nutrients, due to which embryonic development occurs in the egg until the stage of a fully formed young. Larvae, like amphibians, do not exist in reptiles - small copies of adult animals immediately hatch from eggs: turtles, crocodiles, lizards or snakes.

Embryos in eggs develop usually due to the heat received from external environment. Reptiles do not have real incubation and heating of masonry, as in birds, and therefore incubation can last a long time - several months. The hatchlings are completely independent. They are able to immediately move, hunt and defend themselves from enemies.

In most reptiles, the various phases of reproduction - courtship and mating, gestation, oviposition, hatching - occur at strictly limited times of the year and are timed to coincide with the most favorable for this. weather conditions.

Oviparous and live birth

Initially, reptiles reproduced precisely by laying eggs (the so-called "egg production"). However, this method had a number of disadvantages. Having laid eggs, the female, in general, could no longer help her future offspring. It was left to its own devices. It is good if the place where the eggs are laid is warm enough, if it is not flooded with rain, if various predators do not get them (after all, even ants are not averse to profiting from nutritious eggs). However, in nature such a favorable combination of circumstances is rare. Laid eggs are often, too often lost, do not produce offspring. One of possible solutions- ...carry masonry with you! Indeed, if the eggs are not laid immediately, but remain in the body of the female, then they find themselves in much more favorable conditions: some little thing like an ant will no longer be afraid of them, from more large predator the female can hide with the offspring; own mother can lie down in a warm place and hide from heat, cold or flooding, providing best conditions incubation; finally, she will choose the most suitable place for the birth of the cubs. In the course of evolution, in many groups of reptiles at once, females began to store eggs in their bodies until the cubs began to hatch. True, all crocodiles and turtles lay only eggs, but live births have formed in many other branches of the reptile family tree. Viviparous were, for example, fossil marine lizards - ichthyosaurs. Of modern reptiles, many snakes and lizards bring live cubs. Scientists have calculated that during the evolution of reptiles, in their different groups, live birth occurred at least 35 times! There are many examples when one species reproduces by egg production, and the other, its close “relative”, by live birth. No need to look far: of the two most common in Central Russia one species of lizard - a nimble lizard - lays eggs, and the other - viviparous - brings cubs (that's why it is called so).

But if live birth is such a wonderful solution to many problems, why not all species of reptiles have switched to this progressive method? The fact is that in nature you have to pay for everything, and in something winning, animals will definitely lose in something.

Spindle with newly born offspring

The transition to live birth has its drawbacks. If you look at it, carrying eggs "in itself" is a heavy burden for the female. After all, she loses her mobility, which means that she more often becomes a victim of predators and cannot forage as successfully as before. At the same time, it is not so much her personal sad fate that is important, but the fact that as a result she will leave fewer offspring than she could. During the time that the female carries the developing eggs, she would lay another clutch. This is what happens in nature: viviparous species they bring offspring once a season, and those who lay eggs have time to make two or even three clutches. Further, since bearing cubs weakens the mother, she often has to "skip" the next breeding season in order to regain strength. If a clumsy female with a clutch becomes a victim of a predator, both she herself and her developing cubs die, and besides, there will be no offspring that could be born to her in the future.

Reptiles breed on land. Fertilization is internal. Reptiles reproduce in three ways:

- egg production, that is, the female lays eggs;



- egg production when the embryo develops in an egg in the mother's genital tract, it feeds on the nutrients of the egg, from which it hatches shortly after its deposition. (Remember, which are still characteristic of vertebrates egg production and ovoviviparity.);

live birth, in which the embryo develops in the mother's body and receives nutrients from it. For this method of reproduction, the female gives birth to babies. This type of reproduction is inherent only in some sea snakes.

The sex of the offspring that will be born depends on the temperature of incubation of reptile eggs. In crocodiles and turtles incubated at temperatures above +30 C, only females are born, and if the temperature is below this indicator, only males.

In May-June, the female lizard lays in a shallow hole or mink from 6 to 16 large eggs containing stock nutrients- yolk. It is necessary for the embryo to have the opportunity to develop for a long time and be born in the form of a small lizard. Lizard eggs are always covered with a soft, leathery scale-like shell (the shell of turtle and crocodile eggs is hard). Shkaralupna shell prevents damage and drying of the egg. However, in a too dry environment, the eggs can dry out, so sufficient moisture is a necessary condition for the normal development of the embryo.

The development of embryos in eggs continues for two months. At the end of summer, young lizards 4-5 cm long appear from them, which immediately begin an independent life, feeding on the smallest insects. In October, the young are hiding for the winter. The lizard grows throughout its life, its length can be about 25 centimeters. In the second or third year of life, having a length of up to 10 cm, it becomes sexually mature.

The life span of reptiles is the longest among all vertebrates. Lizards live up to 20 years, snakes up to 60, and crocodiles and turtles can live up to 100. Lives longer elephant tortoise - over 150 years old.

Reptiles are land animals. The transition to a completely terrestrial lifestyle took place due to such features of the adaptation: a dense cover of the body, which prevents moisture loss, and the presence of eggs with protective shells, as a result of which reptiles are able to breed on land.

Terms and concepts: class Reptiles, or Reptiles; horny scales, scutes, rings, autotomy, thoracic, tubular-lumbar, caudal spine, chest, intercostal muscles, pelvic kidneys, ureters, urethra, larynx, bronchi, Jacobson's organ, live birth, yolk, shell membrane.

Check yourself. 1. What are the features external structure And individual development distinguish reptiles from amphibians? 2. The structure of the integument of reptiles? 3. What is the difference between the skeletons of a lizard and a frog? 4. Name the fundamental differences in the excretion system of lizards and frogs and explain what caused them. 5. What sense organs are most important for the orientation of a lizard? 6. What are oviparous, ovoviviparous and live births?

How do you think? Why do lizards become active in hot sunny weather, and become lethargic during cold weather?

reptiles- typical terrestrial animals and the main way of their movement is crawling, crouching on the ground. Key features the structure and biology of reptiles helped their ancestors leave the water and spread widely across the land. These features are primarily internal fertilization And oviposition, rich in nutrients and covered with a dense protective shell, which contributes to their development on land.

The body of reptiles has protective formations in the form scales, dressing them with a continuous cover. The skin is always dry, evaporation through it is impossible, so they can live in dry places. Reptiles breathe exclusively with the help of lungs, which, compared with the lungs of amphibians, have a more complex structure. intensive breathing with lungs became possible due to the appearance of a new part of the skeleton in reptiles - chest. Rib cage formed by a number of ribs connected on the dorsal side with the spine, and on the abdominal side with the sternum. The ribs, due to special muscles, are mobile and contribute to the expansion of the chest and lungs during inhalation and their subsidence at the moment of exhalation.

With a change in structure respiratory system closely related changes in blood circulation. Most reptiles have a three-chambered heart and two circles of blood circulation (as in amphibians). However, the structure of the reptile heart is more complex. In his ventricle there is a septum, which, at the moment of contraction of the heart, almost completely divides it into the right (venous) and left (arterial) halves.

Such a structure of the heart and other than in amphibians, the location of the main vessels more strongly delimits the venous and arterial flows, therefore, the body of reptiles is supplied with blood that is more saturated with oxygen. The main vessels of the systemic and pulmonary circulations are typical of all terrestrial vertebrates. The main difference between the pulmonary circulation of amphibians and reptiles is that the skin arteries and veins have disappeared in reptiles and the pulmonary circulation includes only the pulmonary vessels.

About 8,000 are known today existing species reptiles found on all continents except Antarctica. Modern reptiles are divided into groups: primordial lizards, scaly, crocodiles And turtles.

Reproduction of reptiles

Fertilization in land reptiles internal: the male injects spermatozoa into the cloaca of the female; they penetrate the egg cells, where fertilization occurs. In the body of the female, eggs develop, which she lays on land (buries in a hole). Outside, the egg is covered with a dense shell. The egg contains a supply of nutrients, due to which the development of the embryo occurs. Not larvae emerge from the eggs, as in fish and amphibians, but individuals capable of independent life.

Primal Lizard Squad

TO primordial lizards refers to "living fossil" - tuatara- the only species that has survived to our time only on small islands near New Zealand. This is a sedentary animal, leading a predominantly nocturnal lifestyle and appearance lizard-like. Hatteria in its structure has features that make reptiles related to amphibians: the vertebral bodies are biconcave, a chord is preserved between them.

Joy of the scaly

typical representative scaly - quick lizard. Its appearance indicates that it is a terrestrial animal: five-fingered limbs do not have swimming membranes, fingers are armed with claws; the legs are short, in connection with which the body, when moving, seems to be crawling along the ground, now and then in contact with it - groveling (hence the name).

lizards

Although the legs of the lizard are short, it can run fast, nimbly eluding pursuers into its burrow or climbing a tree. This was the reason for her name - nimble. The head of the lizard is connected to the cylindrical body with the help of the neck. The neck is poorly developed, but still gives the head of the lizard some mobility. Unlike a frog, a lizard can turn its head without turning its whole body. Like all land animals, it has through nostrils, and eyes have eyelids.

Behind each eye in a small depression is eardrum connected to the middle and inner ear. From time to time, the lizard protrudes from its mouth a long, thin, forked tongue at the end - the organ of touch and taste.

The body of the lizard, covered with scales, rests on two pairs of legs. The shoulder and thigh bones are parallel to the ground, causing the body to sag and drag along the ground. Attached to the thoracic vertebrae are the ribs that form the rib cage, which protects the heart and lungs from injury.

Digestive, excretory and nervous system lizards are basically similar to the corresponding amphibian systems.

Respiratory organs - lungs. Their walls have a cellular structure, which greatly increases their surface. The lizard does not have cutaneous respiration.

The brain of a lizard is better developed than that of amphibians. Although it has the same five sections, but the hemispheres of the forebrain are larger in size, the cerebellum and medulla oblongata are much more massive.

The quick lizard is very widely distributed from the Black Sea to the Arkhangelsk region, from Baltic Sea to Transbaikalia. In the north, it gives way to a viviparous lizard similar to it, but more adapted to the cold climate. In the southern regions there are many different types lizards. Lizards live in minks, which in summer weather leave in the morning and evening, but no further than 10-20 m from the mink.

They feed on insects, slugs, and in the south - locusts, caterpillars of butterflies and beetles. During the day, one lizard can destroy up to 70 insects, plant pests. Therefore, lizards deserve protection as very useful animals.

The temperature of the body of the lizard is unstable (the animal is active only in the warm season), it drops sharply even if a cloud runs into the sun. With a longer decrease in temperature, the lizard loses mobility and stops eating. For the winter, she hibernates; can tolerate freezing and cooling of the body to -5 °, -7 ° C, while all the vital processes of the animal are significantly slowed down. Gradual warming returns the lizard to an active life.

In addition to the quick and viviparous lizard, there are many other types of lizards. Distributed in Ukraine and the Caucasus large green lizard: in desert areas - agama lizards with a long flexible and non-brittle tail.

predatory lizard gray monitor lizard desert dweller Central Asia. Its length is up to 60 cm. The monitor lizard eats arthropods, rodents, eggs of turtles and birds. The largest specimens of monitor lizards discovered by scientists herpetologists (a science that studies reptiles) on the island of Komolo reach 36 cm. In the northern regions, a legless lizard is common - spindle.

Chameleons

Chameleons in appearance they resemble medium-sized lizards, with a helmet-like outgrowth on the head and a body compressed from the sides. It is a highly specialized animal adapted to an arboreal lifestyle. His fingers are fused like pincers, with which he tightly wraps around the branches of trees. The long and prehensile tail is also used for climbing. The chameleon has a very peculiar eye structure. The movements of the left and right eyes are not coordinated and independent of each other, which gives some advantages when catching insects. An interesting feature chameleon is its ability to change the color of the skin - a protective device. Chameleons are common in India, Madagascar, Africa, Asia Minor and southern Spain.

snakes

The squamous order, in addition to lizards, includes snakes. Unlike chameleons, snakes are adapted for crawling on their stomachs and for swimming. In connection with wave-like movements, the legs gradually completely lost the role of organs of movement, only some snakes preserved their rudiments (boa constrictor). Snakes move by bending their legless body. Adaptability for crawling manifested itself in the structure internal organs snakes, some of them have completely disappeared. snakes don't have Bladder and just one easy one.

They see snakes badly. Their eyelids are fused, transparent and cover their eyes like a watch glass.

Among the snakes there are non-venomous and poisonous species. The largest non-venomous snake - boa- lives in the tropics. There are boas up to 10 m long. They attack birds and mammals, suffocate their prey by squeezing it with their body, and then swallow it whole. Large boas living in tropical forests are also dangerous to humans.

From Not poisonous snakes widespread snakes. The common one is already easily distinguished from poisonous snakes by two orange crescent spots on the head and round pupils of the eyes. He lives near rivers, lakes, ponds, eating frogs, and sometimes small fish, swallowing them alive.

Venomous snakes are viper, cobra, or spectacle snake , rattlesnake and etc.

Viper easily recognizable by the long zigzag dark stripe running along the back. In the upper jaw of the viper are two poisonous teeth with tubules inside. Through these tubules, a poisonous liquid secreted by the victim enters the wound. salivary glands snakes, and the victim, such as a mouse or a small bird, dies.

Destroying great amount mice and locusts, vipers are beneficial to man. However, their bites can cause long-term illness and even death in animals and even humans. The venom of snakes such as asian cobra, american rattlesnake.

The wounds formed when a person is bitten by a snake look like two red dots. A painful swelling quickly develops around them, gradually spreading throughout the body. A person develops drowsiness, cold sweat appears, nausea, delirium appear, in severe cases death occurs.

When a person is bitten by a venomous snake, urgent first aid measures must be taken, remove excess poison near the wound with blotting paper, cotton wool or a clean cloth, if possible, disinfect the bite site with manganese solution, strictly protect the wound from contamination, give the victim strong tea or coffee, and ensure peace. Then get him to the hospital as soon as possible for an emergency injection of anti-snake serum. Where there are poisonous snakes, you can not walk barefoot. Care must be taken when picking berries, protecting your hands from snake bites.

Otrad crocodiles

crocodiles- these are large and most highly organized predatory reptiles, adapted to an aquatic lifestyle, live in tropical countries. Nile crocodile spends most of its life in the water, where it swims well, using a strong, laterally compressed tail, as well as hind limbs that have swimming membranes. The eyes and nostrils of the crocodile are elevated, so it is enough for him to put his head out of the water a little and he already sees what is happening above the water, and also breathes atmospheric air.

On land, crocodiles are not very agile and, in case of danger, rush into the water. They quickly drag their prey into the water. These are various animals that the crocodile lies in wait for at watering places. It can also attack humans. Crocodiles hunt mainly at night. During the day, often large and in groups lie motionless on the shallows.

Turtle Squad

Turtles differ from other reptiles in well-developed strong shell. It is formed from bone plates, covered on the outside with horny substance, and consists of two shields: the upper convex and the lower flat. These shields are connected to each other from the sides, and there are large gaps in front and behind the junctions. The head and forelimbs are exposed from the front, and the hind limbs from the back. Almost all aquatic turtles- predators, land - herbivores.

Turtles usually lay hard-shelled eggs on land. Turtles grow slowly, but they are among the centenarians (up to 150 years). There are giant turtles (soup turtle up to 1 m long. Weight - 450 kg. bog turtle- up to 2 m and up to 400 kg). They are commercial objects.

Meat, fat, eggs are used for food, and a variety of horn products are made from the shell. We have one kind of turtle - bog turtle lives up to 30 years. It hibernates for the winter.

They developed new, drier habitats. Reptiles gained an advantage in the struggle for existence due to the emergence of adaptations to prevent the loss of water by the body and the transition to the terrestrial method of reproduction.

Having conquered the land, the ancient reptiles reached an unprecedented flourishing. In the Mesozoic, they were represented by a huge variety of forms.

The class Reptiles, or Reptiles, is represented mainly by terrestrial animals. They reproduce and develop exclusively on land. Even those species that live in water breathe atmospheric air and come ashore to lay their eggs.

The body of a reptile consists of a head, body and tail. It is protected from drying out by the skin. Breathing is exceptionally light. A more complex structure of the circulatory system allowed reptiles to more successfully adapt to conditions ground-air environment habitat compared to amphibians. Reptiles are cold-blooded animals, their activity depends on the ambient temperature, so most species live in areas with a hot climate.

Many species of reptiles have an elongated body, such as snakes, lizards, and crocodiles. In turtles, it is round and convex. The skin of reptiles is dry, without glands. She's covered horny scales, or shields, and almost does not participate in gas exchange. As they grow, reptiles periodically shed their skin. Reptiles have two pairs of legs on the sides of their bodies. The exceptions are snakes and legless lizards. The eyes of reptiles are protected by eyelids and a nictitating membrane (third eyelid).

Respiratory system

Due to the loss of skin respiration, the lungs of reptiles are well developed and have a cellular structure. The ribcage is first formed in the skeleton. It consists of the thoracic spine, ribs and sternum (absent in snakes). The volume of the chest can change, so reptiles breathe by sucking air into the lungs, and not swallowing it like amphibians.

Nervous system

The brain of reptiles is larger and more complex than that of amphibians: the size of the cerebellum and cerebral hemispheres has increased. This is associated with their better coordination, mobility, development of the senses, especially vision and smell.

Nutrition and excretion

Most reptiles are predators, only land and sea ​​turtles feed mainly on plants. The organs of excretion are the kidneys. The need to use water sparingly leads to the fact that the excretory products of reptiles contain almost no water.

Circulatory system

The heart of reptiles is three-dimensional: it consists of a ventricle and two atria. Unlike amphibians, in the ventricle of reptiles, incomplete septum dividing it in half. There are two circles of blood circulation.

In reptiles, internal fertilizationnot associated with water. This gave an advantage in the struggle for existence over amphibians, and they settled widely on land. Reptiles reproduce by laying eggs. After fertilization, the embryo is covered with egg and embryonic membranes. They provide protection, participate in the processes of nutrition and excretion.

Predatory reptiles regulate the number of their prey. Lizards and snakes, feeding on insects and rodents, benefit humans. Snake venom is used in medicine. Beautiful and valuable products are made from crocodile and snake skin.

If you meet a viper in the forest, remember that it never attacks a person first and will try to hide. You should not step on her, try to catch or kill her. The bite victim should be given tea and taken to the doctor as soon as possible. Incisions, the imposition of a tourniquet, the intake of alcohol can only harm him.

Reptiles are true land animals that breed on land. They live in countries with a hot climate, and as they move away from the tropics, their number noticeably decreases. The limiting factor in their distribution is temperature, since these cold-blooded animals are active only in warm weather, in cold and hot they burrow into holes, hide in shelters or fall into a stupor.

In biocenoses, the number of reptiles is small and therefore their role is hardly noticeable, especially since they are not always active.

Reptiles feed on animal food: lizards - insects, molluscs, amphibians, snakes eat many rodents, insects, but at the same time they pose a danger to domestic animals and humans. herbivores land turtles cause damage to gardens and orchards, aquatic - feed on fish and invertebrates.

The meat of many reptiles is used by humans as food (snakes, turtles, large lizards). Crocodiles, turtles and snakes are exterminated for the sake of the skin and horny shell, and therefore the number of these ancient animals has been greatly reduced. There are crocodile farms in the USA and Cuba.

The Red Book of the USSR includes 35 species of reptiles.

About 6300 species of reptiles are known, which are distributed throughout the globe much wider than amphibians. Reptiles live mainly on land. Warm and moderately humid regions are most favorable for them, many species live in deserts and semi-deserts, but only a very few penetrate into high latitudes.

Reptiles (Reptilia) are the first terrestrial vertebrates, but there are some species that live in the water. These are secondary aquatic reptiles, i.e. their ancestors moved from a terrestrial way of life to an aquatic one. Of the reptiles, venomous snakes are of medical interest.

Reptiles, together with birds and mammals, make up the superclass of higher vertebrates - amniotes. All amniotes are true terrestrial vertebrates. Thanks to the embryonic membranes that have appeared, they are not associated with water in their development, and as a result of the progressive development of the lungs, adult forms can live on land in any conditions.

Reptile eggs are large, rich in yolk and protein, covered with a dense parchment-like shell, develop on land or in the mother's oviducts. The water larva is absent. A young animal hatched from an egg differs from adults only in size.

Class characteristic

Reptiles are included in the main trunk of the evolution of vertebrates, since they are the ancestors of birds and mammals. Reptiles appeared at the end of the Carboniferous period, approximately 200 million years BC, when the climate became dry, and in some places even hot. This created favorable conditions for the development of reptiles, which turned out to be more adapted to living on land than amphibians.

A number of features contributed to the advantage of reptiles in competition with amphibians and their biological progress. These should include:

  • a shell around the embryo (including the amnion) and a strong shell (shell) around the egg, protecting it from drying out and damage, which made it possible to reproduce and develop on land;
  • further development of the five-fingered limb;
  • improvement of the structure of the circulatory system;
  • progressive development of the respiratory system;
  • appearance of the cerebral cortex.

The development of horny scales on the surface of the body, which protect against adverse effects, was also important. environment primarily from the drying action of the air.

reptile body divided into head, neck, torso, tail and limbs (absent in snakes). Dry skin is covered with horny scales and scutes.

Skeleton. The spinal column is divided into five sections: cervical, thoracic, lumbar, sacral and caudal. Skull bony, occipital condyle one. In the cervical spine there is an atlas and an epistrophy, due to which the head of the reptiles is very mobile. Limbs end with 5 fingers with claws.

musculature. It is much better developed than in amphibians.

Digestive system. The mouth leads to the oral cavity, equipped with a tongue and teeth, but the teeth are still primitive, of the same type, they serve only to capture and hold prey. digestive tract consists of the esophagus, stomach and intestines. On the border of the large and small intestines is the rudiment of the caecum. The intestine ends with a cloaca. Developed digestive glands (pancreas and liver).

Respiratory system. In reptiles, the respiratory tract is differentiated. The long trachea branches into two bronchi. The bronchi enter the lungs, which look like cellular thin-walled sacs with big amount internal partitions. The increase in the respiratory surface of the lungs in reptiles is associated with the absence of skin respiration. Breathing is only lung. The breathing mechanism of the suction type (breathing occurs by changing the volume of the chest), more advanced than that of amphibians. Conductive airways (larynx, trachea, bronchi) are developed.

excretory system. Represented by secondary kidneys and ureters that flow into the cloaca. It also opens the bladder.

Circulatory system. There are two circles of blood circulation, but they are not completely separated from each other, due to which the blood is partially mixed. The heart is three-chambered (in crocodiles, the heart is four-chambered), but consists of two atria and one ventricle, the ventricle is divided by an incomplete septum. The large and small circles of blood circulation are not completely separated, but the venous and arterial flows are more strongly separated, so the body of reptiles is supplied with more oxygenated blood. Separation of flows occurs due to the septum at the time of contraction of the heart. When the ventricle contracts, its incomplete septum, attached to the abdominal wall, reaches the dorsal wall and separates the right and left halves. The right half of the ventricle is venous; the pulmonary artery departs from it, the left aortic arch begins above the septum, carrying mixed blood: the left part of the ventricle is arterial: the right aortic arch originates from it. Converging under the spine, they merge into an unpaired dorsal aorta.

The right atrium receives venous blood from all organs of the body, and the left atrium receives arterial blood from the lungs. From the left half of the ventricle, arterial blood enters the vessels of the brain and anterior part of the body, from the right half of the venous blood goes to the pulmonary artery and then to the lungs. Mixed blood from both halves of the ventricle enters the trunk region.

Endocrine system. Reptiles have all the endocrine glands typical of higher vertebrates: the pituitary, adrenals, thyroid, etc.

Nervous system. The brain of reptiles differs from the brain of amphibians in the large development of the hemispheres. The medulla oblongata forms a sharp bend, characteristic of all amniotes. The parietal organ in some reptiles functions as a third eye. The rudiment of the cerebral cortex appears for the first time. There are 12 pairs of cranial nerves that emerge from the brain.

The sense organs are more complex. The lens in the eyes can not only mix, but also change its curvature. In lizards, the eyelids are movable; in snakes, the transparent eyelids are fused. In the organs of smell, part of the nasopharyngeal passage is divided into olfactory and respiratory sections. The internal nostrils open closer to the pharynx, so reptiles can breathe freely when they have food in their mouths.

reproduction. Reptiles have separate sexes. Sexual dimorphism is pronounced. Sex glands are paired. Like all amniotes, reptiles are characterized by internal insemination. Some of them are oviparous, others are ovoviviparous (that is, a cub immediately emerges from a laid egg). Body temperature is not constant and depends on the ambient temperature.

Systematics. modern reptiles are divided into four subclasses:

  1. lizards (Prosauria). Primal lizards are represented by a single species - tuatara ( Sphenodon punctatus), which is among the most primitive reptiles. The tuatara lives on the islands of New Zealand.
  2. scaly (Squamata). This is the only relatively large group of reptiles (about 4000 species). The scaly ones are
    • lizards. Most species of lizards are found in the tropics. This order includes agamas, poisonous lizards, monitor lizards, real lizards, etc. Lizards are characterized by well-developed five-fingered limbs, movable eyelids and eardrums [show] .

      The structure and reproduction of the lizard

      quick lizard. The body is 15-20 cm long on the outside covered with dry skin with horny scales that form quadrangular scutes on the abdomen. The hard cover interferes with the uniform growth of the animal, the change of the horny cover occurs by molting. In this case, the animal sheds the upper stratum corneum of the scales and forms a new one. The lizard molts four to five times during the summer. At the ends of the fingers, the horny cover forms claws. The lizard lives mainly in dry sunny places in the steppes, sparse forests, shrubs, gardens, on the slopes of hills, railway and highway embankments. Lizards live in pairs in minks, where they hibernate. They feed on insects, spiders, mollusks, worms, eat many pests of agricultural crops.

      In May-June, the female lays 6 to 16 eggs in a shallow hole or burrow. The eggs are covered with a soft fibrous leathery shell that protects them from drying out. The eggs have a lot of yolk, the protein shell is poorly developed. All development of the embryo takes place in the egg; after 50-60 days, a young lizard hatches.

      In our latitudes, lizards are often found: agile, viviparous and green. All of them belong to the family of real lizards of the scaly order. The agama family belongs to the same order (steppe agama and roundheads - inhabitants of the deserts and semi-deserts of Kazakhstan and Central Asia). The scaly ones also include chameleons that live in the forests of Africa, Madagascar, India; one species lives in southern Spain.

    • chameleons
    • snakes [show]

      The structure of snakes

      Snakes also belong to the scaly order. These are legless reptiles (some retain only the rudiments of the pelvis and hind limbs), adapted to crawling on their belly. Their neck is not expressed, the body is divided into head, trunk and tail. The spine, which has up to 400 vertebrae, has great flexibility due to additional joints. It is not divided into departments; almost every vertebra bears a pair of ribs. In this case, the chest is not closed; the sternum of the girdle and limbs are atrophied. Only a few snakes have preserved a vestige of the pelvis.

      The bones of the facial part of the skull are movably connected, the right and left parts of the lower jaw are connected by very well stretchable elastic ligaments, just as the lower jaw is suspended from the skull by stretchable ligaments. Therefore, snakes can swallow big booty even bigger than a snake's head. Many snakes have two sharp, thin, poisonous teeth bent back, sitting on the upper jaws; they serve to bite, detain prey and push it into the esophagus. Poisonous snakes have a longitudinal groove or duct in the tooth, through which the poison flows into the wound when bitten. The poison is produced in altered salivary glands.

      Some snakes have developed special organs of thermal sense - thermoreceptors and thermolocators, which allows them to find warm-blooded animals in the dark and in burrows. The tympanic cavity and membrane are atrophied. Eyes without eyelids, hidden under transparent skin. The skin of the snake becomes keratinized from the surface and is periodically shed, i.e., molting occurs.

      Previously, up to 20-30% of victims died from their bites. Due to the use of special therapeutic sera, mortality has decreased to 1-2%.

  3. Crocodiles (Crocodilia) are the most highly organized reptiles. They are adapted to an aquatic lifestyle, in connection with which they have swimming membranes between the fingers, valves that close the ears and nostrils, and a palatal curtain that closes the pharynx. Crocodiles live in fresh waters, go out on land to sleep and lay eggs.
  4. turtles (Chelonia). Turtles are covered above and below with a dense shell with horny shields. Their chest is motionless, so the limbs take part in the act of breathing. When they are drawn in, the air leaves the lungs, when they are pulled out, it enters again. Several species of turtles live in the USSR. Some species, including the Turkestan tortoise, are eaten.

The value of reptiles

Anti-snake sera are currently used for therapeutic purposes. The process of making them is as follows: horses are sequentially injected with small, but ever-increasing doses snake venom. After the horse is sufficiently well immunized, blood is taken from it and a therapeutic serum is prepared. Recently, snake venom has been used in medicinal purposes. It is used for various bleeding as a hemostatic agent. It turned out that with hemophilia, it can increase blood clotting. The drug from snake venom - vipratox - reduces pain in rheumatism and neuralgia. To obtain snake venom and to study the biology of snakes, they are kept in special nurseries. Several serpentaries operate in Central Asia.

Over 2 thousand species of snakes are non-venomous, many of them feed on harmful rodents and bring significant benefits national economy. Of the non-venomous snakes, snakes, copperheads, snakes, and steppe boas are common. Water snakes sometimes eat juvenile fish in pond farms.

Meat, eggs and tortoise shells are very valuable, they are export items. The meat of monitor lizards, snakes, and some crocodiles is used as food. The valuable skin of crocodiles and monitor lizards is used for the manufacture of haberdashery and other products. Crocodile breeding farms have been set up in Cuba, the United States and other countries.