reptile eyes testify to their way of life. At different types we observe a peculiar structure of the organs of vision. To protect their eyes, some "cry", others have eyelids, and still others "wear glasses".
reptile vision , like the variety of species, is very different. The way the eyes are located on the reptile's head largely determines how much the animal sees. When the eyes are set on both sides of the head, the visual fields of the eyes do not overlap. Such animals see well everything that happens on both sides of them, but their spatial vision is very limited (they cannot see the same object with both eyes). When the eyes of a reptile are set in front of the head, the animal can see the same object with both eyes. This position of the eyes helps reptiles more accurately determine the location of prey and the distance to it. IN land turtles and many lizards have eyes set on both sides of the head, so they can see everything that surrounds them well. The Cayman tortoise has excellent spatial vision because its eyes are set in front of its head. The eyes of chameleons, like cannons in defense towers, can rotate independently 180° horizontally and 90° vertically - they see behind them.

How do snakes show a source of heat?.
The most important sense organ of the snake is the tongue in combination with Jacobson's organ. However, reptiles have other adaptations necessary for successful hunting. In order to identify prey, snakes need more than just eyes. Some snakes can perceive heat radiated from the animal's body.
The pit-headed snakes, which include the real grimuchnik, got their name due to the fact that they have a paired sense organ, in the form of facial pits located between the nostrils and the eye. With the help of this organ, snakes can feel warm-blooded animals by the difference in body temperatures and external environment with an accuracy of 0.2 ° C. The size of this organ is only a few millimeters, but it can capture the infrared rays emitted by potential prey and transmit the information received through the nerve endings to the brain. The brain perceives this information, analyzes it, so the snake has a clear idea of ​​what kind of prey it met on the way and where exactly it is located. Different kinds reptiles are very differently seen and perceived the world. The field of view, its expressiveness and ability to distinguish colors depend on how the animal's eyes are set, on the shape of the pupils, as well as on the number and type of light-sensitive cells. In reptiles, vision is also associated with a way of life.
color vision
Many of the lizards can perfectly distinguish colors, which for them is an important means of communication. Some of them on a black background recognize scarlet poisonous insects. In the retina of the eyes of diurnal lizards there are special elements of color vision - flasks. Giant tortoises are color-aware, some of them responding particularly well to red light. They are even thought to be able to see infrared light, which the human eye cannot see. Crocodiles and snakes are color blind.
American night lizards react not only to shape, but also to color. However, their retina still contains more rods than cones.
reptile vision
The class of reptiles, or reptiles, includes crocodiles, alligators, turtles, snakes, geckos, and lizards such as the tuatara. The reptile needs to get accurate information about the size and color of its potential prey. In addition, the reptile must detect and quickly react when other animals approach and determine who it is - a potential partner, a young animal of the same species, or an enemy that can attack it. Reptiles that live underground or in water have rather small eyes. Those of them that live on earth are more dependent on visual acuity. The eyes of these animals are arranged in the same way as the eyes of a person. Their most part is the eyeball with the optic nerve. In front of it is the cornea, which transmits light. On the cornea - the iris. In its center is the pupil, which narrows or expands, letting a certain amount of light into the retina. The lens is located under the pupil, through which the rays enter the light-sensitive back wall of the eyeball - the retina. The retina is made up of layers of light and color sensitive cells connected by optic nerves to the brain, where all signals are sent and where an image of an object is created.
Eye protection
In some species of reptiles, eyelids are used to protect the eyes, as in mammals. However, reptilian eyelids differ from mammalian eyelids in that the lower eyelid is larger and more mobile than the upper eyelid.
The snake's gaze seems to be glassy, ​​since its eyes are covered with a transparent film, which is formed by the fused upper and lower eyelids. This protective coating is a kind of "glasses". During molting, this film comes off with the skin. "Points" are worn by lizards, but only a few. Geckos do not have eyelids. To cleanse the eyes, they use the tongue, sticking it out of the mouth and licking the eye membrane. Other reptiles have a "parietal eye". This is a bright spot on the head of a reptile; like an ordinary eye, it can perceive certain light stimuli and transmit signals to the brain. Some reptiles use their lacrimal glands to protect their eyes from pollution. When sand or other debris gets into the eyes of such reptiles, the lacrimal glands secrete a large number of liquid that cleans the eyes of the animal, while it seems as if the reptile is "crying". Soup turtles use this method.
The structure of the pupil

The pupils of reptiles testify to their way of life. Some of them, for example, crocodiles, pythons, geckos, hatteria, snakes, lead a nocturnal or twilight lifestyle, and take sunbaths during the day. They have vertical pupils that dilate in the dark and constrict in the light. In geckos, pinholes are visible on constricted pupils, each of which focuses an independent image onto the retina. Together they create the necessary sharpness, and the animal sees a clear image.

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Thermolocators of a different design have recently been studied in snakes. This discovery deserves more details.

In the east of the USSR, from the Caspian Trans-Volga region and the Central Asian steppes to Transbaikalia and the Ussuri taiga, medium-sized Poisonous snakes, nicknamed muzzles: their head is covered on top not with small scales, but with large shields.

People who have looked at muzzles up close claim that these snakes seem to have four nostrils. In any case, on the sides of the head (between the real nostril and the eye), two large (larger nostrils) and deep fossae are clearly visible in muzzles.

Cottonmouths are close relatives rattlesnakes America, which locals sometimes called kvartonaritsy, that is, four-nosed. This means that rattlesnakes also have strange pits on their faces.

All snakes with four "nostrils" are combined by zoologists into one family of so-called crotalids, or pit-headed ones. Pit snakes are found in America (North and South) and in Asia. In their structure, they are similar to vipers, but differ from them in the mentioned pits on the head.

For more than 200 years, scientists have been solving a puzzle given by nature, trying to determine what role these pits play in the life of snakes. What assumptions were made!

They thought that these were organs of smell, touch, hearing enhancers, glands that secrete lubricant for the cornea of ​​​​the eyes, traps of subtle air vibrations (like the lateral line of fish) and, finally, even air blowers that deliver oxygen to the oral cavity, allegedly necessary for the formation of poison.

Careful studies carried out by anatomists thirty years ago showed that the facial pits of rattlesnakes are not connected with either the ears, or the eyes, or

by any other known authority. They are depressions in the upper jaw. Each hole at a certain depth from the inlet is divided by a transverse partition (membrane) into two chambers - internal and external.

The outer chamber lies in front and opens outwards with a wide funnel-shaped opening, between the eye and the nostrils (in the area of ​​\u200b\u200bthe auditory scales). The rear (inner) chamber is completely closed. Only later was it possible to notice that it communicates with the external environment by a narrow and long canal, which opens on the surface of the head near the anterior corner of the eye with an almost microscopic pore. However, the size of the pore, when necessary, can apparently increase significantly: the opening is provided with an annular closing muscle.

The partition (membrane) separating both chambers is very thin (about 0.025 mm thick). Dense weaves of nerve endings permeate it in all directions.

Undoubtedly, the facial pits are the organs of some senses. But what?

In 1937, two American scientists - D. Noble and A. Schmidt published great job, in which they reported the results of their many years of experience. They managed to prove, the authors argued, that the facial pits are thermolocators! They capture heat rays and determine the location of the heated body emitting these rays by their direction.

D. Noble and A. Schmidt experimented with rattlesnakes artificially devoid of all known to science sense organs. Electric bulbs wrapped in black paper were brought to the snakes. As long as the lamps were cold, the snakes paid no attention to them. But then the light bulb warmed up - the snake immediately felt it. She raised her head, worried. The light bulb is still closer. The snake made a lightning throw and bit the warm "victim". I didn’t see her, but she bit exactly, without a miss.

Experimenters have found that snakes detect heated objects, the temperature of which is at least 0.2 degrees Celsius above the surrounding air (if they are brought closer to the muzzle itself). Warmer objects are recognized at a distance of up to 35 centimeters.

In a cold room, thermolocators work more accurately. They are obviously adapted for night hunting. With their help, the snake searches for small warm-blooded animals and birds. Not smell, but body heat betrays the victim! After all, snakes have poor eyesight and smell, and completely unimportant hearing. A new, very special feeling came to their aid - thermal location.

In the experiments of D. Noble and A. Schmidt, an indicator that the snake found a warm light bulb was its throw. But after all, the snake, of course, even before it rushed to the attack, already felt the approach of a warm object. This means that it is necessary to find some other, more accurate signs by which one could judge the subtlety of the thermolocation sense of the snake.

American physiologists T. Bullock and R. Cowles conducted more thorough research in 1952. As a signal announcing that the object was detected by the snake's thermolocator, they chose not the reaction of the snake's head, but a change in biocurrents in the nerve serving the facial fossa.

It is known that all processes of excitation in the body of animals (and humans) are accompanied by reactions arising in muscles and nerves. electric currents. Their voltage is small - usually hundredths of a volt. These are the so-called "biocurrents of excitation". Biocurrents are easy to detect with the help of electrical measuring instruments.

T. Bullock and R. Kauls anesthetized snakes by introducing a certain dose of curare poison. They cleaned one of the nerves branching in the membrane of the facial fossa from muscles and other tissues, brought it out and clamped it between the contacts of a device that measures biocurrents. Then the facial pits were subjected to various influences: they were illuminated with light (without infrared rays), strong-smelling substances were brought close, irritated strong sound, vibration, tweaks. The nerve did not react: there were no biocurrents.

But it was worth bringing a heated object closer to the snake's head, even just human hand(at a distance of 30 centimeters), as excitement arose in the nerve - the device recorded biocurrents.

Illuminated the pits with infrared rays - the nerve was even more excited. The weakest reaction of the nerve was found when it was irradiated with infrared rays with a wavelength of about 0.001 millimeters. The wavelength increased - the nerve was more excited. The greatest reaction was caused by the longest-wavelength infrared rays (0.01 - 0.015 millimeters), that is, those rays that carry the maximum thermal energy emitted by the body of warm-blooded animals.

It also turned out that rattlesnake thermolocators detect not only warmer, but even colder objects than the surrounding air. It is only important that the temperature of this object be at least a few tenths of a degree higher or lower than the surrounding air.

The funnel-shaped openings of the facial pits are directed obliquely forward. Therefore, the range of the thermolocator lies in front of the snake's head. Up from the horizontal, it occupies a sector of 45, and down - at 35 degrees. To the right and to the left of the longitudinal axis of the body of the snake, the field of action of the thermolocator is limited to an angle of 10 degrees.

physical principle, on which the thermolocator device of snakes is based, is completely different from that of squids.

Most likely, in the thermoscopic eyes of squids, the perception of a heat-radiating object is achieved through photochemical reactions. Here, probably, processes of the same type take place as on the retina of an ordinary eye or on a photographic plate at the moment of exposure. The energy absorbed by the organ leads to the recombination of light-sensitive (in squids - heat-sensitive) molecules, which act on the nerve, causing the representation of the observed object in the brain.

Snake thermolocators act differently - according to the principle of a kind of thermoelement. The thinnest membrane separating the two chambers of the facial fossa is exposed to two different temperatures from different sides. The inner chamber communicates with the external environment through a narrow channel, the inlet of which opens in opposite side from the working field of the locator.

Therefore, the ambient temperature is maintained in the inner chamber, (Neutral level indicator!) The outer chamber, with a wide opening - a heat trap, is directed towards the object under study. The heat rays that it emits heat the front wall of the membrane. According to the temperature difference on the inner and outer surfaces of the membrane, simultaneously perceived by the nerves in the brain, there is a feeling of a radiating thermal energy subject.

In addition to pit snakes, thermolocation organs have been found in pythons and boas (in the form of small pits on the lips). The little pits above the nostrils in the African, Persian, and some other species of viper seem to serve the same purpose.

To be fair, snakes are not as blind as is commonly believed. Their vision varies greatly. For example, tree snakes have fairly sharp eyesight, and those leading an underground lifestyle are only able to distinguish light from darkness. But for the most part, they are really blind. And during the molting period, they can generally miss during the hunt. This is due to the fact that the surface of the snake's eye is covered with a transparent cornea and at the time of molting it also separates, and the eyes become cloudy.

What they lack in vigilance, however, snakes make up for with a thermal sensing organ that allows them to track the heat radiated by prey. And some representatives of reptiles are even able to track the direction of the heat source. This organ was called a thermolocator. In fact, it allows the snake to "see" prey in the infrared spectrum and successfully hunt even at night.

snake hearing

With regard to hearing, the statement that snakes are deaf is true. They lack the outer and middle ear, and only the inner ear is almost completely developed.

Instead of an organ of hearing, nature gave snakes a high vibrational sensitivity. Since they are in contact with the ground with their whole body, they very keenly feel the slightest vibrations. However, snake sounds are still perceived, but in a very low frequency range.

Smell of a snake

The main sense organ of snakes is their surprisingly subtle sense of smell. An interesting nuance: when immersed in water or when buried in sand, both nostrils close tightly. And what is even more interesting - in the process of smelling, a long tongue forked at the end takes a direct part.

With a closed mouth, it protrudes out through a semicircular notch in the upper jaw, and during swallowing it hides in a special muscular vagina. With frequent vibrations of the tongue, the snake captures microscopic particles of odorous substances, as if taking a sample, and sends them into the mouth. There she presses her tongue against two pits in the upper palate - Jacobson's organ, which consists of chemically active cells. It is this organ that provides the snake with chemical information about what is happening around, helping it find prey or notice a predator in time.

It should be noted that in snakes living in water, the tongue works just as effectively underwater.

Thus, snakes do not use their tongue to determine taste in the truest sense. It is used by them as an addition to the body to determine the smell.

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Of all the many different animals living on Earth, snake eyes are able to distinguish colors and shades. Vision for a snake plays a big role in life, although it is not the main sense for familiarization with outside world. Serpents on our planet approx. As many people know from school, snakes belong to the scaly order. Their habitat is territories with warm or temperate climate. .

How are the eyes of a snake arranged?

The snake eye, unlike other animals, does not differ in visual acuity. And all because their eyes are covered with a thin leathery film, they are very cloudy, and this greatly affects visibility. During molting, the snake parted with the old skin, and with it the film. Therefore, after molting, snakes are especially “big-eyed”. Their vision becomes sharper and clearer for several months. Because of the film on the eyes, people from ancient times gave the snake's gaze a special coldness and hypnotic power.

Most snakes that live near humans are harmless and do not pose any danger to humans. But there are also poisonous ones. Snake venom is used for hunting and protection.

Depending on the way of hunting - in the daytime or at night, the shape of the pupil of snakes changes. For example, the pupil is round, and the snakes leading the twilight hunt have acquired vertical and elongated eyes with long slits.

But the most unusual eyes have the appearance of whip-shaped snakes. Their eye is very similar to a keyhole located horizontally. Because of this unusual structure the snake's eye skillfully uses its binocular vision - that is, each eye forms a complete picture of the world.

But the main sense organ in snakes is still the sense of smell. This organ is the main one for thermolocation of vipers and pythons. The sense of smell allows you to catch the warmth of your victims in pitch darkness and accurately determine their location. Snakes that are non-venomous strangle or wrap their prey with their body, and there are those who swallow their prey alive. Most of the snakes are small, no more than one meter. During the hunt, the eyes of the snake are focused on one point, and their forked tongue, thanks to the Jacobson's organ, traces the subtlest smells in the air.