Do all reptiles lay eggs on land? Reptile class
Reptile eggs are similar in structure to birds' eggs. On the outside, they are covered with a leathery shell, on the surface of which, in some groups, lime may be deposited. This occurs in crocodiles and some turtles. In lizards, the egg shell is always leathery.
The presence of a dense leathery and calcareous shell in reptile eggs is due to the fact that their development occurs on land. And on land, humidity is very low - only 3-15%, so the developing embryo needs protection to prevent water loss. The calcareous shells of crocodiles and some turtles are especially good at preventing eggs from drying out.
Inside a reptile's egg, just like a bird's, there is a yolk surrounded by a layer of protein. This is the stock nutrients for the developing embryo.
Shape and size of reptile eggs?
I teach a lesson about reptile eggs with children at the Oceanarium museum (Vladivostok). At the live exhibition we can observe the Nile crocodile and the common iguana. And also turtles: Chinese trionix and red-eared.
Reptile eggs, video about Chinese Trionix:
This short video introduced you to the Chinese Trionics, the development of which will be discussed below.
It so happened that the topic “development of reptiles” fell on the day of the celebration Orthodox Easter. Therefore, we considered the egg as a symbol of life and carried out a kind of research.
I asked the guys to compare the shape and size of the eggs of reptiles known to us and some fish, also presented at the live and “dry” exhibitions of the Oceanarium museum.
Study of the shape and size of eggs of reptiles and fish
Each study participant received a form with a life-size outline of the eggs of the studied animal species.
In progress collective discussion We completed the task and wrote the number of the animal’s name next to the outline of the egg.
"Portrait" of a Nile crocodile
Then we went to the museum exposition and already on the spot next to the terrariums and aquariums the guys heard brief information about the characteristics of reproduction and development of each animal.
For example, Nile crocodile begins to reproduce at the age of 10 years. The female lays eggs in a nest, which she builds from plant debris, and then fills the nest with sand. The entire time the eggs are incubating, which is about three months, she does not leave the nest. There are an average of 40-60 eggs in a clutch. And the surprising thing is that they are very similar in shape and size to chickens. The shell of the Nile crocodile egg is calcareous.
Nile crocodiles are caring parents!
Female Nile crocodiles Very caring mothers. As soon as they hear grunting sounds from the nest, they begin to dig out the eggs and help the hatchlings free themselves from the shell. Female She has already chosen a shallow body of water in advance, into which she transfers her cubs immediately after their “birth”. Often she collects them in her mouth and carries them in her mouth. The crocodiles remain in this reservoir under the supervision of their mother for another 1.5–2 months. Video about a female Nile crocodile
The father Nile crocodile usually helps the female guard the nest, and sometimes the growing children, while they are in a kind of “nursery” - a shallow body of water into which their mother transferred them.
Turtles don't care about their young
But turtles don’t care about their offspring at all. For example, Chinese trionix (Far Eastern soft-shelled turtle, Chinese leatherback turtle).
Chinese Trionix
Trionyx females lay their eggs on sandbanks or pebbles close to the water. The nesting hole is usually located at a depth of 15-20 cm. The shape of the eggs is spherical, the color is yellowish or slightly beige. The diameter of the egg is approximately 2 cm.
One female makes 2-3 clutches during the breeding season. The total number of eggs laid is from 18 to 75. Why is there such a spread? Clutches of large old Chinese Trionyx females have more eggs than young ones.
40-60 days after the eggs are laid, the turtles hatch and immediately head to the water. The length of their shell is only 3 cm. Therefore, they travel 15-20 m to the water in 40-45 minutes. Of course it takes a long time. In saving water, they immediately hide under stones or burrow into the ground.
The common iguana is not a caring mother!
And another example of “bad” motherhood from the world of reptiles. Wikipedia gives detailed information about the reproduction of the common or green iguana.
This type of iguana digs its nest on dry sand dunes. The depth of the nest indicates its reliability - 45-100 cm. The female iguana lays many eggs - up to 70, so this process of laying eggs takes several days (up to three or more).
Egg shell common iguana soft leathery, but quite durable. Eggs white oval in shape, with a diameter of about 1.5 cm and a length of about 3.5-4.0 cm.
After laying eggs, having carefully buried the hole, the lizard never returns to this place.
Interesting fact: several iguanas can lay eggs in one hole if there are few suitable places for laying eggs.
Conclusion
So, let’s summarize some of the article on the reproduction and development of reptiles:
- Using the example of studying the shape of reptile eggs, you saw how a simple task helps children focus their attention on the museum exhibit object you have chosen.
- A brief summary of information on the reproduction, development and care of offspring in reptiles: Chinese trionix, Nile crocodile, and common iguana is provided.
The next article will be about fish reproduction and will introduce you to the largest fish eggs. We will once again turn to the form depicting the outlines of eggs.
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Representatives of reptiles (more than 4 thousand species) are true terrestrial vertebrates. Due to the appearance of the embryonic membranes, they are not associated with water in their development. As a result of the progressive development of the lungs, adult forms can live on land in any conditions. Reptiles living in the species are secondary aquatic, i.e. their ancestors switched from a terrestrial lifestyle to an aquatic one.
Remember! Reptiles and reptiles are the same class!
Reptiles, or creeping things, appeared at the end 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 traits contributed to the advantage of reptiles in competition with amphibians and their biological progress. These include:
- The membranes around the embryo 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;
- development of five-fingered limbs;
- improvement of the structure of the circulatory system;
- progressive development of the respiratory system;
- appearance of the cerebral cortex big brain.
The development of horny scales on the surface of the body, protecting against adverse influences, was also important. environment, first of all, from the drying effect of air. The prerequisite for the appearance of this device was liberation from skin respiration due to the progressive development of the lungs.
A typical representative The reptile can be the sand lizard. Its length is 15-20cm. It has a well-defined protective coloration: greenish-brown or brown, depending on its habitat. During the day, lizards are easy to see in a sun-warmed area. At night they crawl under stones, into holes and other shelters. They spend the winter in the same shelters. Their food is insects.
On the territory of the CIS, the most widespread are: in the forest zone - the viviparous lizard, in the steppe - the sand lizard. The spindle is a lizard. It reaches 30-40 cm, has no legs, which reminds it of a snake, this often costs it its life. The skin of reptiles is always dry, devoid of glands, and covered with horny scales, scutes or plates.
The structure of reptiles
Skeleton. The spinal column is already divided into cervical, thoracic, lumbar, sacral and caudal sections. The skull is bony, the head is very mobile. The limbs end in five fingers with claws.
The muscles of reptiles are much better developed than those of amphibians.
Digestive system . Mouth leads to oral cavity, equipped with a tongue and teeth, but the teeth are still primitive, of the same type, and serve only for capturing and holding prey. The alimentary canal consists of the esophagus, stomach, and intestines. At the border of the large and small intestines the rudiment of the cecum is located. The intestines end in a cloaca. Digestive glands are developed: pancreas and liver.
Respiratory system. The respiratory tract is much more differentiated than in amphibians. There is a long trachea that 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 surfaces of the lungs in reptiles is associated with the lack of cutaneous respiration.
Excretory system represented by the kidneys and ureters flowing into the cloaca. The bladder also opens into it.
Circulatory system . Reptiles have two circles of blood circulation, but they are not completely separated from each other, due to which the blood is partially mixed. The heart has three chambers, but the ventricle is divided by an incomplete septum.
Crocodiles already have a real four-chambered heart. The right half of the ventricle is venous, and the left part is arterial - the right aortic arch originates from it. Converging under the spinal column, they unite into the unpaired dorsal aorta.
Nervous system and sensory organs
The brain of reptiles differs from the brain of amphibians in the greater development of the hemispheres and cerebral vault, as well as the separation of the parietal lobes. Appears for the first time, the cerebral cortex. 12 pairs of cranial nerves arise from the brain. The cerebellum is somewhat more developed than in amphibians, which is associated with more complex coordination of movements.
At the front end of the lizard's head there is a pair of nostrils. The sense of smell in reptiles is better developed than in amphibians.
The eyes have eyelids, upper and lower, in addition, there is a third eyelid - a translucent nictitating membrane that constantly moisturizes the surface of the eye. Behind the eyes is a rounded eardrum. Hearing is well developed. The organ of touch is the tip of the forked tongue, which the lizard constantly sticks out of its mouth.
Reproduction and regeneration
Unlike fish and amphibians, which have external fertilization (in water), reptiles, like all non-amphibious animals, have internal fertilization, in the body of the female. The eggs are surrounded by embryonic membranes that enable development on land.
The female lizard quickly lays 5-15 eggs in a secluded place at the beginning of summer. The eggs contain nutritional material for the developing embryo and are surrounded on the outside by a leathery shell. A young lizard emerges from the egg, looking like an adult. Some reptiles, including some species of lizards, are ovoviviparous (i.e., a baby immediately emerges from a laid egg).
Many species of lizards, when grabbed by the tail, break it off with sharp lateral movements. Throwing back the tail is a reflex response to pain. This should be considered as an adaptation thanks to which lizards escape from enemies. A new one grows in place of the lost tail.
Diversity of modern reptiles
Modern reptiles are divided into four orders:
- Protolizards;
- Scaly;
- Crocodiles;
- Turtles.
Protolizards represented by a single type - tuateria, which is one of the most primitive reptiles. The tuateria lives on the islands of New Zealand.
Lizards and snakes
Scaly animals include lizards, chameleons and snakes. This is the only one regarding large group reptiles - about 4 thousand species.
Lizards are characterized by well-developed five-fingered limbs, movable eyelids and the presence of an eardrum. This order includes agamas, poisonous teeth - poisonous lizards, monitor lizards, real lizards, etc. Most species of lizards are found in the tropics.
Snakes are adapted to crawling on their belly. Their neck is not pronounced, so the body is divided into head, torso and tail. The spinal column, which contains up to 400 vertebrae, is highly flexible thanks to additional articulations. The belts, limbs and sternum are atrophied. Only some snakes have preserved a rudimentary pelvis.
Many snakes have two poisonous teeth on their upper jaws. The tooth has a longitudinal groove or duct through which the poison flows into the wound when bitten. The tympanic cavity and membrane are atrophied. The eyes are hidden under transparent skin, without eyelids. The snake's skin becomes keratinized on the surface and is periodically shed, i.e. moulting occurs.
Snakes have the ability to open their mouths very wide and swallow their prey whole. This is achieved by the fact that a number of skull bones are connected movably, and the lower jaws in front are connected by a very tensile ligament.
The most common snakes in the CIS are snakes, copperheads, snakes. The steppe viper is listed in the Red Book. For its habitat, it avoids agricultural lands, but lives on virgin lands, which are becoming less and less, which threatens it with extinction. Feeds steppe viper(like other snakes) are predominantly mouse-like rodents, which is certainly useful. Its bite is poisonous, but not fatal. She can attack a person only by accident, being disturbed by him.
Bites poisonous snakes- cobras, ephas, vipers, rattlesnakes and others - can be fatal to humans. Among the fauna, the gray cobra and sand efa, which are found in Central Asia, are very dangerous, as well as the viper, found in Central Asia and Transcaucasia, and the Armenian viper, which lives in Transcaucasia. Bites common viper and copperhead are very painful, but usually not fatal to humans.
The science that studies reptiles is called herpetology.
IN Lately snake venom is used in medicinal purposes. Snake venom is used for various bleedings as a hemostatic agent. It turned out that some drugs obtained from snake venom reduce pain due to rheumatism and diseases nervous system. For getting snake venom In order to study the biology of snakes, they are kept in special nurseries.
Crocodiles are the most highly organized reptiles, having a four-chambered heart. However, the structure of the partitions in it is such that venous and arterial blood are partially mixed.
Crocodiles are adapted to an aquatic lifestyle, and therefore have swimming membranes between the toes, valves that close the ears and nostrils, and a velum that closes the pharynx. Crocodiles live in fresh waters, come to land to sleep and lay eggs.
Turtles are covered above and below with a dense shell with horny scutes. Their chest is motionless, so their limbs take part in the act of breathing - when they are drawn in, the air leaves the lungs, when they stick out, it enters them. Several species of turtles live in Russia. Some species are eaten, including the Turkestan tortoise, which lives in Central Asia.
Ancient reptiles
It has been established that in the distant past (hundreds of millions of years ago) various types of reptiles were extremely common on Earth. They inhabited land, water, and less often air. Most species of reptiles became extinct due to climate change (cold temperatures) and the rise of birds and mammals, with which they could not compete. Extinct reptiles include orders of dinosaurs, wild-toothed lizards, ichthyosaurs, flying lizards, etc.
Dinosaur Squad
This is the most diverse and numerous group of reptiles that has ever lived on Earth. Among them were both small animals (the size of a cat and smaller) and giants, whose length reached almost 30 m and weight - 40-50 tons.
Large animals had small heads long neck and a powerful tail. Some dinosaurs were herbivores, others were carnivores. The skin either had no scales or was covered with a bone shell. Many dinosaurs ran galloping on their hind limbs, leaning on their tail, while others moved on all four legs.
Squad Animal-toothed
Among the ancient land reptiles there were representatives of a progressive group, which resembled animals in the structure of their teeth. Their teeth were differentiated into incisors, canines and molars. The evolution of these animals went in the direction of strengthening their limbs and belts. In the process of evolution, mammals arose from them.
Origin of reptiles
Fossil reptiles have great importance, since they once dominated the globe and from them came not only modern reptiles, but also birds and mammals.
Living conditions at the end of the Paleozoic changed dramatically. Instead of warm and humid climate cold winters appeared and dry and hot climate. These conditions were unfavorable for the existence of amphibians. However, under such conditions, reptiles began to develop, whose skin was protected from evaporation, a terrestrial method of reproduction, a relatively highly developed brain and other progressive characteristics appeared, which are given in the characteristics of the class.
Based on a study of the structure of amphibians and reptiles, scientists came to the conclusion that there are great similarities between them. This was especially true for ancient reptiles and stegocephalians.
- In very ancient lower reptiles, the vertebral column had the same structure as in stegocephals, and the limbs - like in reptiles;
- the cervical region of reptiles was as short as that of amphibians;
- the chest bone was missing, i.e. this chest they didn't have one yet.
All this suggests that reptiles evolved from amphibians.
Reptiles are the ancient inhabitants of our planet. They differ in classes and types, each of which has distinctive characteristic. This article will introduce the reader to the environment in which and how the reptile embryo develops.
General information
Reptiles are those that have adapted to life in land conditions. These first terrestrials are characterized by the following characteristics:
- Reproduction occurs by eggs and on land.
- Breathing is carried out by the lungs. Its mechanism is of the suction type, that is, when the reptile breathes, the volume of the chest changes.
- The presence of horny scales or scutes on the skin.
- Almost all reptiles lack skin glands.
- The division of the ventricle of the heart by septa can be complete or incomplete.
- The skeleton of reptiles and muscles have undergone progressive development due to an increase in their mobility: the girdle of the limbs has strengthened and their position in relation to the body and to each other has changed. The spine was divided into different sections, and the head became more mobile.
Reptiles today are represented by scattered remains of reptiles that lived on the planet many thousands of years ago. Now there are six thousand species of them, almost three times more than amphibians.
Living reptiles are divided into the following orders of reptiles:
- beakheads;
- scaly;
- crocodiles;
- turtles.
The first species is represented by a single representative - the tuateria, which has an external resemblance to a lizard, but its structure is distinguished by primitive features. The habitat of the tuateria is New Zealand.
Crocodiles
This order includes the following types of reptiles: caiman, gharial, Nile crocodile. aquatic lifestyle are characterized by high organization, the presence of a four-chambered heart and a septum that separates the toes of the hind legs. The eyes raised high above the muzzle help crocodiles observe their prey.
Females lay eggs on the shore near reservoirs, but in a high, non-flooded place. Nests are built from nearby materials. Gharials use sand to bury their eggs. Crocodiles in tropical regions mix grass and fallen leaves with soil to build a nest.
The female is capable of laying up to 100 eggs, which are fertilized by different partners. Laying occurs at night, several weeks after the mating process. The eggs are large, similar in size to duck eggs.
And where the embryo develops occurs in the egg, which is located in the mother’s body. During laying, an embryo is already developing in it. The female is always near the nest, protecting future offspring from predators. After three months, small crocodiles hatch.
Turtles
This order includes turtles: red-eared, marsh and steppe. Their body is covered with a bony shell fused with vertebrae and ribs. The jaws of turtles do not have teeth. Air enters the lungs in the same way as in amphibians.
Before laying, turtles build nests. Aquatic reptiles are in the sand on the shores of reservoirs, and land reptiles are on the ground, in a dug hole. They no longer show any concern for their offspring.
Many species of turtles mate in April and early May. Only next spring can we expect them to be adapted to life without parents from birth.
Orders of reptiles: squamate
These include lizards:
- viviparous;
- yellowbell;
- iguana.
Almost all of them, except the yellow-bellied one, have four limbs for movement and eyes protected by eyelids. The eyelids of reptiles of this order are movable.
Egg laying time occurs in May-June. The animal acquires a hole or hole of shallow depth and places eggs there. There are from 6 to 16 pieces. Large egg. Inside is the yolk, which contains food reserves for the embryo. In lizards the egg shell is soft, in crocodiles and turtles it is hard.
Snakes are snakes, vipers, and copperheads. They are legless reptiles, when moving, their body bends. The structure of reptiles is distinguished by a long section of the spine of the body and the absence of a chest. Snakes have one lung. The shell of the eyes is formed by fused eyelids.
Reptiles have the ability to swallow big size prey. This is achieved through movably connected lower jaws. The front teeth of poisonous snakes are equipped with a channel through which the poison enters the victim.
Snakes reproduce sexually. According to this feature, they are viviparous and oviparous. In the natural environment, reproduction is seasonal. The gestation period for snakes varies. In snake families it is 48 days, in pythons it is from 60 to 110.
Towards the end of pregnancy, snakes begin to build nests. Their locations may be small trees, fallen trunks, rodent burrows, or anthills. The clutch consists of 3-40 eggs. They have an elongated or oval shape- it depends on the type of reptile.
Almost all species of snakes do not care about their offspring. The exceptions are the four-striped snake, the mud snake and King Cobra. They guard the eggs until the snakes hatch.
Reproduction
This happens on land. Fertilization in reptiles is internal. Their offspring are born in three ways:
- Oviparity. This is the case when the question of where the embryo of reptiles develops can be answered - in the egg. Natural environment for him it is the mother's reproductive tract. It receives nutrition from the egg, after the laying of which the baby develops from the embryo.
- Viviparity. It is not inherent in all reptiles, but only in certain species of sea snakes. Where does the reptile embryo develop? This occurs in the mother's body. From it he receives everything he needs for his development.
- Incubation method. It is used to increase the number of a certain type of reptile. From turtles and crocodiles, females will be born if the temperature in the incubator is above 30°C, and males - if it is lower.
And where does the reptile embryo develop in some vipers and viviparous lizards? Here the eggs remain in the mother's oviduct for a very long time. They form a baby, which is immediately born from the mother’s body or hatches from the egg after it is laid.
Reptile eggs
Reptiles evolved on land. Adapting to the land environment, their eggs were covered with a fibrous shell. Modern lizards and snakes have the most primitive forms of egg shells. And to prevent the eggs from drying out, their development occurs in moist soil.
Dense shells not only perform protective function. They are the first sign of adaptation of eggs for development on land. The larval stage is eliminated, which increases the nutrient content here. The reptile egg is large.
The second stage in the adaptation of eggs for survival and further development in a land environment is the release of the protein shell from the walls of the oviduct. It stores the water supplies needed by the embryo. Crocodile and turtle eggs are covered with such a shell. Their fibrous shell is replaced by a lime shell. Water reserves do not pass through it, and with such protection from drying out, embryos can develop in any weather conditions.
17. Reptiles. Features of their structure, reproduction and development. Main systematic groups. Biology of lizards, turtles, snakes.
A class of terrestrial vertebrates that includes modern turtles, crocodiles, beaked animals, amphisbaenians, lizards and snakes.
Structure. The outer skin of reptiles forms scales or scutes. The change of horny cover occurs through complete or partial molting, which in many species occurs several times a year. Thick and dry skin contains scent glands. IN axial skeleton 5 sections of the spine: cervical, trunk, lumbar, sacral and caudal. In snakes, the spine is clearly divided only into the trunk and caudal sections; the sternum is absent. The skull of reptiles is much more ossified than that of amphibians. A pair of forelimbs of reptiles consists of a shoulder, forearm and hand. A pair of hind limbs - from the thigh, lower leg and foot. There are claws on the phalanges of the limbs. The nervous system of reptiles is represented by the brain and spinal cord. Reptiles have 6 main senses: vision, smell, taste, thermal sensitivity, hearing and touch. Since the body is covered with scales, reptiles do not have cutaneous respiration (with the exception of soft-bodied turtles and sea snakes), and the lungs are the only respiratory organ. There is a trachea and bronchi. All modern reptiles are cold-blooded animals. The excretory system of reptiles is represented by the kidneys, ureters and bladder.
Reproduction. Reptiles are dioecious animals, bisexual reproduction. The male reproductive system consists of a pair of testes. The female reproductive system is represented by the ovaries. Majority reptiles reproduces by laying eggs. The incubation period lasts from 1-2 months. up to a year or more.
Lifestyle. Due to the unstable body temperature, the activity of modern birds reptiles largely depends on the ambient temperature. When the body is cooled to 8-6 °C, most people reptiles stops moving. Reptiles can be exposed to prolonged sun exposure and tolerate increases in body temperature up to 40 °C. Avoiding overheating, reptiles They go into the shadows and hide in holes. Great impact on activity reptiles provide seasonal changes climatic conditions; in temperate countries reptiles fall into winter torpor, and in dry heat conditions - into summer torpor. For most reptiles, the characteristic method of movement is crawling. Many species are good swimmers.
Nutrition. Most reptiles are carnivores. Some (for example, agamas, iguanas) have a mixed diet. There are also almost exclusively herbivorous reptiles (land turtles).
Biology of lizards. Most lizards (with the exception of some legless forms) have developed limbs to varying degrees. Although legless lizards are similar in appearance to snakes, they retain a sternum, and most have limb girdles. Many species of lizards are capable of throwing off part of their tail (autotomy). After some time, the tail is restored, but in a shortened form. During autotomy, special muscles compress the blood vessels in the tail, and almost no bleeding occurs. Most lizards are predators. Small and average size species feed mainly on various invertebrates: insects, arachnids, mollusks, worms. Large predatory lizards (monitor lizards, tegus) attack small vertebrates: other lizards, frogs, snakes, small mammals and birds, and also eat the eggs of birds and reptiles. Most lizards lay eggs. Lizard eggs have a thin leathery shell, less often, as a rule in geckos, a dense, calcareous shell. Number of eggs various types can range from 1-2 to several dozen.
The female may lay eggs one or more times throughout the year. She always lays eggs in the most secluded places - in cracks, under snags, etc. Some geckos glue eggs to tree trunks and branches, and on rocks. As a rule, after laying eggs, lizards do not return to them.
Biology of turtles. A characteristic feature of turtles is their shell, which consists of a convex dorsal (carapace) and flat ventral (plastron) shields. Both shields are connected by side bridges or leather. The basis of the shell is made up of skin ossifications, as well as ribs and vertebrae. Lumpy thickenings give the frame increased strength. A durable shell significantly reduces the mobility of land turtles. The turtles' brain and sensory organs are poorly developed. A sedentary lifestyle also corresponds to a low metabolic rate. Turtles live up to 100 years. Some of them live on land, where they dig holes. Other turtles live in the sea, coming ashore only during the breeding season. But most turtles lead a semi-aquatic lifestyle in rivers, lakes and swamps. During unfavorable periods (winter, drought), these turtles can hibernate. They can go without food for several months. In the second or third years of life, sexual maturity occurs; eggs are laid in sand.
Biology of snakes. The snake's body is divided into head, torso and tail. In most cases, the skeleton consists of a skull and a vertebral column (141 to 435 vertebrae in some fossil forms), to which the ribs are attached. Snakes are perfectly adapted to absorbing large prey, this is reflected in the structure of the skeleton. The right and left halves of the lower jaws are connected movably, the ligaments have special extensibility. The tops of the teeth are directed backwards: when swallowing food, the snake seems to “sit” on it, and the food bolus gradually moves inward. Snakes do not have a sternum and the ribs end freely. Therefore, the part of the body in which the digested prey is located can be greatly stretched.
Many snakes are poisonous. Their upper jaw has large canalized or grooved teeth. The poison, produced by modified salivary glands, enters the base of the tooth and flows down a canal or groove to the top. There is no bladder.
The brain of snakes is relatively small, but the spinal cord is well developed, therefore, despite the primitiveness of reactions, snakes are distinguished by good coordination of movements, their swiftness and accuracy.
The surface layer of the skin forms scutes and scales in the form of elongated plates, arranged in a tiled manner; longitudinal elevations - ribs - are often noticeable on them. They play a big role in the movement of snakes living among rocks or in trees.
Snakes eat everything. Their diet includes a wide variety of animals: from worms to small ungulates. And everyone also knows that they eat insects and birds. Almost all snakes hunt live prey, and only a few prefer carrion.
The digestive system of all snakes is similar: they swallow food whole without chewing it.
The size of the victim depends on the size of the snake itself.
Some snakes favorable conditions can bear offspring up to several times per season, others do not reproduce every year (for example, the Caucasian viper). Usually the cubs hatch from eggs, but viviparity is also widespread (typical of sea snakes, boa constrictors, and vipers). The female develops a placenta through which the embryos receive oxygen, water and nutrients. Sometimes the female does not have time to lay her clutch, and the cubs hatch inside her reproductive tract. This case is called ovoviviparity (vipers, copperheads).
Reptiles are dioecious and may differ in secondary sexual characteristics. Often these differences are minor or even non-existent. Sometimes males are only larger than females, as is usually the case with species of the genus Lacerta, with the exception of the viviparous lizard (Lacerta vivipara), where the female is larger, which is associated with the development of young in the body. Same thing with viviparous snakes. The males of many species of lizards, snakes and turtles have a swollen tail at the base. This depends on the fact that the double copulatory member is in a collapsed state. In turtles, the sexes can be distinguished by the appearance of the chest shield - in males it is concave, while in females it is flat or convex. In other cases the meaning of secondary sex differences is unclear; for example, the difference in the number of scutes in many snakes, the greater narrowness of the neck. Many female snakes have keeled ridges on their dorsal scales during sexual activity. This sign serves to irritate the female during mating.
The meaning of the differences in color observed in some reptiles is not clear. For example, male Cistudo turtles have red eyes, while females have brown eyes. In the bloodsucker (Calotes versicolor), the body color of the male can change at will. Sometimes it is all brilliant red with black spots; in some cases, the skin color changes only on the head, in others - on the entire body, not excluding the tail. The female remains monochromatic. However, bright colors are not always associated with gender. The sexes may further differ in the presence of numerous projections on the head, for example in some species of chameleon, where the male develops horns similar to those of a rhinoceros. This also includes the ridges on the back of the head and on the back of many iguanas. The so-called femoral pores in male lizards are more highly developed. In some reptiles, males also differ in their voice, and it is possible that it serves to attract females. In geckos and alligators, the voice definitely serves to attract females during the breeding season.
The ratio of the number of individuals of both sexes is not always the same. In snakes it is 1:1, 1:3, 1:4, 4:11. Sometimes the same species has different sex ratios in different areas. Thus, the Chinese form Dinodon septentrionale throughout its habitat gives the numbers 3:13, and in South Asia - 0:8. The smaller number of males is apparently due to the higher mortality of the latter.
On the other hand, sometimes there is a temporary predominance of males. Thus, in Central Asia at the end of summer (August) only male snakes are found, while females are absent and it is unknown where they are at this time.
During the mating period, fighting often occurs between males. Crocodiles ferociously chase each other at this time and get into fights. The same thing is observed in lizards; some of them change color during a fight. During the breeding season, snakes gather in large numbers, curl into balls and hiss until they connect with the female, after which sexual arousal subsides.
In reptiles, during the mating season, love games. Male lizards bite females to force them to mate; the same thing was sometimes observed in turtles, where the males emit a whistling tone, crawl behind the female, bite her on the head and push her until she becomes excited. After mating, the excitement disappears and the individuals disperse. Only rarely is a male and female staying together for a long time. The turtle Testudo polyphemus was observed to live in pairs in burrows. There are several other similar examples.
Most reptiles lay eggs, while others give birth to live young. Eggs are covered with a hard or parchment-like shell. The first state, typical of turtles, is apparently more primitive. Among lizards, shelled eggs are found only in geckos. But their shell hardens only gradually, absorbing carbon dioxide from the air. In snakes, eggs with shells are no longer found. When most snakes lay eggs, they are sticky and stick to objects they come into contact with. They often vary both in size and shape.
The number of eggs is from 2 to 150. Both the number of eggs and the method of reproduction show signs of adaptation to the conditions of the outside world and are determined by them. The highest (up to 400 per year) egg production is observed in sea turtles. This is apparently due to the fact that young turtles are poorly adapted to life in water at first: they swim, but do not dive, are thrown ashore and serve as prey for fish and birds. Excessive increase in body weight from such a mass of eggs and excessive need for nutritional material are avoided by laying eggs in batches and losing the shell. A very small number of eggs can also be considered an adaptive phenomenon. Turtles that breed in China in cultivated areas where animal enemies are almost entirely absent lay a minimal number of eggs (2). Geckos lay more eggs in the south of Asia than in the north, which can be attributed to the presence of their enemy tree snake - Chrisopelea ornata. Climbing forms lay fewer eggs than terrestrial ones.
Eggs are laid either in specially dug holes, or among moss and foliage, in damp warm places. The US snake Diodophys punctatus lays its faces in a variety of places: in dirt thrown out of a quarry, in dust under a rotten tree, in a stump, under a stone, in the passages of ants with dust - generally in damp, but not wet places exposed to the sun. In 95% of cases it is a hole in the ground. Usually the female leaves the eggs to their fate. Only some snakes and crocodiles behave differently; some American forms of the latter make real nests for their eggs in damp places. This nest consists of a layer of plants on which eggs are laid, again then covered with plants. Due to the rotting of plants in the nest, such heat that the nest is smoking. This warmth serves for the rapid development of the young.
In Madagascar, a female crocodile guards the nest until the young develop. The female allegedly recognizes this by the special sound that young crocodiles make in the egg, helps them dig out of the sand and immediately leads them to the water. The female caiman behaves the same way. African crocodiles do not appear to guard their nests. North American alligators lay a nest near the habitat of the female, who rushes at everyone who approaches her, and in this way guards the nest. Here we have an interesting series of gradual complication of instinct, showing how it could arise. As stated in the systematic part, dinosaurs laid eggs in nests.
Some females large snakes(pythons, for example), having laid eggs, lie on them in such a way that they form a flat arch above them, inside which the temperature is 10-12° Celsius higher than the surrounding one, which promotes the development of eggs. The copperhead Ancistrodon does the same. At this time, the female does not take any water or food and protects the eggs from any attack on them. This can also be seen as caring for the offspring. A lizard called teyu (Tupinambis teguixin) excavates termite nests and lays its eggs there. Young lizards emerging from the latter immediately find food in the form of termites.
Many reptiles give birth to live young and are viviparous. The cubs break through the thin membranes of the eggs while still in the mother’s body or immediately after birth. It is more correct to call them not viviparous, but ovoviviparous. Ovoviviparous forms are not known only in crocodiles and turtles. We find this type of reproduction in many lizards, especially those living in the mountains, in many gigantic American snakes, sea snakes, vipers, various snakes and others. Only in a few reptiles do we find true viviparity, when the nutrition of the embryo in the mother’s body occurs with the help of blood vessels the yolk sac, which comes into contact with the vessels of that section of the oviduct, which plays the role of the uterus. Fossil ichthyosaurs (Ichtyosauria) were also viviparous. This feature stood out to them, like sea snakes, in connection with the transition to pelagic life in the sea. Based on the structure of the limbs of ichthyosaurs, it can be judged that ichthyosaurs never came ashore, but led a life similar to the life of modern whales.
The primary form of reproduction in reptiles is reproduction by laying eggs. From it a series of transitions leads to ovoviviparity and further to viviparity. This transition is facilitated in reptiles by the fact that when circumstances unfavorable for the laying of eggs occur, the latter can be delayed for weeks and the egg remains in the body. The conditions under which viviparity arose in reptiles as an adaptation to them can be named as follows: a) purely aquatic life(Hydrophis); in species of large oviparous genera (Natrix, Elaphe) that transition to life in water (Natrix annularis, Elaphe rufodorsata), viviparity develops; b) distribution in cold areas, at the cold boundaries of their vertical and horizontal range, where night temperatures are too low for eggs and require protection in the mother's body (Phrynocephalus from the Central Asian highlands, Lacerta vivipara, Vipera herus, Ancistrodon in Asia). Living in Tibet at an altitude of 4,200 m but near hot springs, the Natrix species lays eggs; c) life underground (Scincus officinalis, Echis carinata, Vipera ammodytes); d) life on trees and shrubs (Dryophis, Boiga). If any group of reptiles has lived since ancient geological times in conditions that cause viviparity, then the latter is characteristic of all members of the group. Thus, in Scincidae, the skinks, viviparity is a characteristic of the entire group.
The duration of incubation varies among reptiles. It depends on the conditions in which the eggs develop; On average, snakes last between 2 and 3 months. Hatching from an egg can take many hours, up to a day. Not all eggs hatch at the same time. It takes 2-3 days for snakes to emerge from all eggs in a clutch.
Having emerged from the egg or being born alive, reptiles grow quickly but reach sexual maturity very slowly: for example, the Chinese snake (Natrix piscator) in the 4th year, the tree snake (Dryophis) at the end of the 2nd year, male pythons at the end 3rd and females - 4th year. But reptiles reach a very old age. Regarding turtles, for example, there are cases where they survived in captivity for up to 54 years. The giant tortoise (Testudo sunieri) reached the age of 150 years in captivity. There are cases where turtles lived up to 250 years. Great age crocodiles also reach. Reptiles are apparently little susceptible to diseases, although parasites of the protozoa type are often found in the blood of reptiles. It must be assumed that in a natural environment, most reptiles die not from old age and disease, but from a violent death or from some external unfavorable causes. However, there is a suspicion that lizards are carriers and transmitters of certain diseases (for example, leishmaniasis).
