Do snakes have vision? How do snakes see us? There are many ways to see - it all depends on your goals

Reptile eyes indicate their way of life. In different species we observe a unique structure of the visual organs. To protect their eyes, some “cry”, others have eyelids, and still others “wear glasses”.
Reptile vision , like the diversity of species, is very different. How the eyes are positioned on a 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 intersect. 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 a reptile's eyes are set at the front of its 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, the eyes are set on both sides of the head, so they can clearly see everything that surrounds them. The snapping turtle has excellent spatial vision because its eyes are set at the front of its head. Chameleons' eyes, like cannons in defensive towers, can rotate independently 180° horizontally and 90° vertically - they can see behind them.

How do snakes exhibit their heat source?.
The most important sensory organ of a snake is the tongue in combination with Jacobson's organ. However, reptiles also have other adaptations necessary for successful hunting. To identify prey, snakes need more than just their eyes. Some snakes can sense heat emitted by the animal's body.
Pit-headed snakes, which include the true pit snakes, got their name due to the fact that they have a paired sensory organ in the form of facial pits located between the nostrils and the eye. With the help of this organ, snakes can sense warm-blooded animals by the difference in temperature between its body and the external environment with an accuracy of 0.2 ° C. The size of this organ is only a few millimeters, but it can detect infrared rays emitted by potential prey and transmit the received information through nerve endings in the brain. The brain perceives this information and analyzes it, so the snake has a clear idea of ​​what kind of prey it encountered on its way and where exactly it is located. Different types of reptiles see and perceive the world around them very differently. The field of vision, its expressiveness and the 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 related to their lifestyle.
Color vision
Many of the lizards can perfectly distinguish colors, which is an important means of communication for them. Some of them recognize scarlet poisonous insects against a black background. In the retina of the eyes of diurnal lizards there are special elements of color vision - bulbs. Giant tortoises are color-sensitive, and some respond particularly well to red light. They are even thought to be able to see infrared light, which the human eye cannot distinguish. 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 hatteria. The reptile needs to receive 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 may attack it. Reptiles that live underground or in water have rather small eyes. Those of them that live on earth depend more on visual acuity. The eyes of these animals are structured in the same way as human eyes. Their very part is the eyeball with the optic nerve. In front of it is the cornea, which allows light to pass through. The cornea is the iris. At its center is the pupil, which contracts or dilates, allowing a certain amount of light to pass onto the retina. Under the pupil there is a lens through which rays hit 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 the optic nerves to the brain, where all signals are sent and where an image of an object is created.
Eye protection
Some species of reptiles use eyelids to protect their eyes, just like mammals. However, reptile eyelids differ from mammalian eyelids in that the lower eyelid is larger and more mobile than the upper.
The snake's gaze appears glassy because its eyes are covered with a transparent film formed by the fused upper and lower eyelids. This protective coating is a kind of “glasses”. During molting, this film comes off along with the skin. Lizards also wear “glasses,” but only some. Geckos do not have eyelids. To clean their eyes, they use their tongue, sticking it out of their mouth and licking the eye shell. Other reptiles have a "parietal eye". This is a light spot on the head of a reptile; like a regular eye, it can perceive certain light stimuli and transmit signals to the brain. Some reptiles protect their eyes from pollution using lacrimal glands. When sand or other debris gets into the eyes of such reptiles, the lacrimal glands secrete a large amount of fluid that cleanses the animal's eyes, making the reptile seem to "cry." Soup turtles use this method.
Pupil structure

The pupils of reptiles indicate their lifestyle. Some of them, for example, crocodiles, pythons, geckos, hatteria, snakes, lead a nocturnal or twilight lifestyle, and take sunbathing during the day. They have vertical pupils that dilate in the dark and constrict in light. In geckos, pinpoint holes are visible on the 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.

You can read interesting things about penguins on the website kvn201.com.ua.

There are about three thousand snakes on earth. They belong to the scaly order and like to live in places with warm climates. Many people, walking through the forest in an area where snakes may live, wonder if they can see us? Or should we look at our feet so as not to disturb the reptile? The fact is that among the diversity in the animal world, only the eyes of a snake are capable of determining shades and colors, but their visual acuity is weak. For a snake, vision is, of course, important, but not as important as smell. In ancient times, people paid attention to the snake's eye, considering it cold and hypnotic.

How does a snake's eye work?

Reptiles have very dull eyes. This is because they are covered with a film that changes during molting along with the rest of the skin. Because of this, snakes have poor visual acuity. As soon as reptiles shed their skin, their visual acuity immediately increases. During this period they see best. They feel this way for several months.

Most people believe that all snakes are poisonous without exception. This is wrong. Most species are completely harmless. Poisonous reptiles use poison only in case of danger and when hunting. It occurs both during the day and at night. Depending on this, the pupil changes its shape. So, during the day it is round, and at night it is stretched into a gap. There are whip snakes with an inverted keyhole pupil. Each eye is capable of forming an entire picture of the world.

For snakes, the main organ is the sense of smell. They use it as thermolocation. So, in complete silence, they feel the heat generated by a possible victim and indicate its location. Non-poisonous species pounce on prey and strangle it, some of them begin to swallow it alive. It all depends on the size of the reptile itself and its prey. On average, the body of a snake is about one meter. There are both small and large species. Directing their gaze at the victim, they focus it. At this time, their tongue picks up the slightest odors in space.

Thermal locators of a different design have recently been studied in snakes. This discovery is worth telling in more detail.

In the east of the USSR, from the Caspian Trans-Volga region and the Central Asian steppes to Transbaikalia and the Ussuri taiga, there are small poisonous snakes, nicknamed copperheads: their heads are covered on top not with small scales, but with large shields.

People who have examined copperheads 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 than the nostril) and deep pits are clearly visible in copperheads.

Cottonmouths are close relatives of America's rattlesnakes, which locals sometimes call quartonaris, that is, four-nosed snakes. This means that rattlesnakes also have strange pits on their faces.

Zoologists combine all snakes with four “nostrils” into one family, the so-called crotalids, or pitheads. Pit snakes are found in America (North and South) and Asia. In their structure they are similar to vipers, but differ from them in the mentioned pits on the head.

For more than two hundred years, scientists have been solving nature's puzzle, trying to establish what role these pits play in the life of snakes. What assumptions were made!

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

Thorough research by anatomists thirty years ago showed that the facial pits of rattlesnakes are not connected to the ears, eyes, or

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

The external chamber lies in front and opens outward with a wide funnel-shaped opening, between the eye and nostril (in the area of ​​the auditory scales). The rear (inner) camera is completely closed. Only later was it possible to notice that it communicates with the external environment through a narrow and long channel, 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 equipped with an annular closing muscle.

The partition (membrane) separating both chambers is very thin (about 0.025 millimeters thick). Dense interweaving of nerve endings penetrates it in all directions.

Undoubtedly, the facial pits represent organs of some senses. But which ones?

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

D. Noble and A. Schmidt experimented with rattlesnakes artificially deprived of all sense organs known to science. Electric light bulbs wrapped in black paper were brought to the snakes. While the lamps were cold, the snakes did not pay any attention to them. But when the light bulb got hot, the snake immediately felt it. She raised her head and became wary. The light bulb was brought even closer. The snake made a lightning-fast throw and bit the warm “victim.” I didn’t see her, but she bit her accurately, without missing a beat.

Experimenters have found that snakes detect heated objects whose temperature is at least 0.2 degrees Celsius higher than 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 apparently adapted for night hunting. With their help, the snake searches for small warm-blooded animals and birds. It is not the smell, but the warmth of the body that gives away the victim! Snakes have poor eyesight and sense of smell and very poor hearing. A new, very special feeling came to their aid - thermal location.

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

American physiologists T. Bullock and R. Cowles conducted more thorough studies in 1952. As a signal notifying that an 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 electrical currents arising in the muscles and nerves. Their voltage is low - usually hundredths of a volt. These are the so-called “biocurrents of excitation”. Biocurrents are easy to detect using electrical measuring instruments.

T. Bullock and R. Cowles anesthetized snakes by injecting a certain dose of curare poison. We cleared one of the nerves branching in the membrane of the facial fossa from muscles and other tissues, brought it out and pressed 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 to them, and they were irritated with strong sound, vibration, and pinches. The nerve did not react: biocurrents did not arise.

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

They illuminated the pits with infrared rays - the nerve became even more excited. The weakest reaction of the nerve was detected when it was irradiated with infrared rays with a wavelength of about 0.001 millimeters. As the wavelength increased, the nerve became 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 the thermolocators of rattlesnakes detect not only objects that are warmer, but even colder than the surrounding air. It is only important that the temperature of this object is at least a few tenths of a degree higher or lower than the surrounding air.

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

The physical principle on which the thermolocators of snakes are based is completely different from those of squids.

Most likely, in the thermoscopic eyes of squids, the perception of a heat-emitting object is achieved through photochemical reactions. Processes of the same type probably occur here as on the retina of an ordinary eye or on a photographic plate at the time 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 brain to imagine the observed object.

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

Therefore, the ambient air temperature is maintained in the inner chamber (neutral level indicator!) The outer chamber is directed towards the object under study with a wide opening - a heat trap. The heat rays it emits heat the front wall of the membrane. Based on the temperature difference on the inner and outer surfaces of the membrane, which are simultaneously perceived by the nerves in the brain, the sensation of an object emitting thermal energy arises.

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

As an example, let's look at how a square profile pipe with side dimensions of mm and a wall thickness of 6 mm, made of SK steel, is marked: хх5 GOST / SK GOST Performance characteristics and scope of application of square pipes.

The performance characteristics of steel pipes with a square profile are determined both by the material of their manufacture and by the features of their design, which is a closed profile formed from a metal strip. GOST Interstate standard. Bent closed welded square and rectangular steel profiles for building structures. GOST Rolled thin-sheet carbon steel of high quality and ordinary quality for general purpose.

Technical conditions. GOST Rolled thin sheets of high strength steel. Technical conditions. GOST Rolled products made of high strength steel.

General technical conditions. GOST Hot rolled sheets. Active. GOST Group B INTERSTATE STANDARD. Technical specifications GOST Rolled products made of high-strength steel. General technical conditions GOST Hot-rolled sheet products. GOST assortment Rolled products for building steel structures. Home > Directories > GOST, TU, STO > Pipes > Profile pipes > GOST GOST Download. Bent closed welded square and rectangular steel profiles for building structures.

Technical conditions. Steel bent closed welded square and rectangular section for building. Specifications. GOST Rolled thick sheet carbon steel of ordinary quality. Technical conditions. GOST Machines, instruments and other technical products. Designs for various climatic regions. Categories, operating conditions, storage and transportation in terms of the impact of environmental climatic factors. GOST - Rectangular and square profile pipes.

GOST regulates the basic requirements for the production of closed welded profiles for building structures. The range of steel square pipes includes the main sizes: For a square profile: from 40x40x2 to xx14 mm. Carbon steel for universal use. Low-alloy thick-walled steel (from 3 mm or more), according to specifications. Burr removal from longitudinal seams is carried out from the outside of the structure, the following deviations are allowed: 0.5 mm - with a section of profile walls up to 0.4 cm.

GOST Interstate standard. Bent closed welded square and rectangular steel profiles for building structures. Technical conditions. Steel bent closed welded square and rectangular section for building. Specifications. Date of introduction 1 Scope. Technical specifications GOST Rolled thin sheets of high-strength steel. Technical specifications GOST Rolled products made of high-strength steel.

General technical conditions GOST Hot-rolled sheet products. GOST assortment Rolled products for building steel structures. Profiled pipe GOST, GOST Profile pipes of square, oval and rectangular sections are manufactured according to the assortment.

The range of profile pipes corresponds to: GOST standard - (general purpose profile pipe made of carbon steel); - square - GOST - (square profile pipe); - rectangular - GOST - (profile rectangular pipe); - oval - GOST - (oval profile pipe). Welded profile pipes are used in construction, production of metal structures, mechanical engineering and other industries. GOST profile pipe / Dimensions.

Steel grade. Technical conditions. Designation: GOST Status: valid. Classifier of state standards → Metals and metal products → Ordinary quality carbon steel → Long and shaped rolled products.

All-Russian Classification of Products → Equipment for traffic control, maintenance of agricultural machinery and auxiliary communications equipment, metal building structures → Steel building structures.

Categories Post navigation