Why is the big eye of an insect spherical? What does the world look like through the eyes of a common fly? The structure of the compound eye

The organs of vision are developed in most insects. reach the greatest development compound or compound eyes . The number of visual elements - ommatidia, or facets, in the eye of a housefly reaches 4 thousand, and in dragonflies even 28 thousand. The ommatidium consists of a transparent lens, or cornea, in the form of a biconvex lens and a transparent crystal cone lying under it. Together they make optical system. Under the cone is the retina, which perceives light rays. retinal cells connected nerve fibers with the visual lobes of the brain. Each ommatidium is surrounded by pigment cells.

Depending on the perception of light different intensity Distinguish between apposition and superposition types of eyes. The first type of eye structure is characteristic of diurnal insects, the second - nocturnal.

AT apposition eye each ommatidium is isolated in its upper part by pigment from neighboring ommatidia. Thus, each structural unit of the eye works separately from all the others, perceiving only “its own” part of the external space. The overall picture is formed in the brain of an insect, as if from many pieces of a mosaic.

AT superposition eye ommatidia are only partially, albeit along the entire length, protected from lateral rays: they are semi-permeable. On the one hand, it interferes with insects in intense light, on the other hand, it helps them see better at dusk.

Ocelli (dorsal simple eyes)- these are small organs of vision that some adults have and are usually located on the top of the head. Usually presented in the amount of three, while one lies slightly in front, and two more - behind and to the side of the front. They do not contain ommatidium, the structure of simple eyes is greatly simplified. Outside, the cornea is located, consisting of rootagen cells, deeper is the light-perceiving apparatus of retinal (sensitive) cells, even lower are pigment cells that pass into the fibers of the optic nerve.

Of all the varieties of insect eyes, simple eyes have the weakest ability to see. According to some reports, they do not perform at all visual function, and are only responsible for improving the function of compound eyes. This, in particular, is proved by the fact that insects practically do not have simple eyes in the absence of complex ones. In addition, when painting over compound eyes, insects cease to orient themselves in space, even if they have well-defined simple eyes.

Stemmas, or lateral simple eyes- are present in insect larvae with complete metamorphosis. During the pupal stage, they "morph" into compound eyes. They perform a visual function, but, due to the simplified structure, they see relatively poorly. To improve vision, larval ocelli are often presented in larvae in the amount of several pieces. In sawfly larvae, they are similar to dorsal ones, and in butterfly caterpillars they resemble compound eye ommatidia. Caterpillars perceive the shape of objects, distinguish small details on their surface.

The most complex of the sense organs in insects are the organs of vision. The latter are represented by formations of several types, of which the most important are compound faceted eyes of approximately the same structure as the compound eyes of crustaceans.

The eyes consist of separate ommatidia (Fig. 337), the number of which is determined mainly by the biological characteristics of insects. Active predators and good fliers, dragonflies have eyes with up to 28,000 facets each. At the same time, ants (neg. Hymenoptera), especially working individuals of species living underground, have eyes consisting of 8 - 9 ommatidia.

Each ommatidium represents a perfect photooptical sensilla (Fig. 338). It consists of an optical apparatus, including the cornea, a transparent section of the cuticle above the ommatidium, and the so-called crystal cone. Together, they act as a lens. The perceiving apparatus of the ommatidium is represented by several (4 - 12) receptor cells; their specialization has gone very far, as evidenced by their complete loss of flagellar structures. Actually sensitive parts of the cells - rhabdomeres - are clusters of densely packed microvilli, located in the center of the ommatidium and closely adjacent to each other. Together they form photosensitive element eyes are a slave.

Shielding pigment cells lie along the edges of the ommatidium; the latter are quite significantly different in diurnal and nocturnal insects. In the first case, the pigment in the cell is immobile and constantly separates neighboring ommatidia, not allowing light rays to pass from one eye to another. In the second case, the pigment is able to move in the cells and accumulate only in their upper part. In this case, the rays of light fall on the sensitive cells of not one, but several neighboring ommatidia, which noticeably (almost two orders of magnitude) increases the overall sensitivity of the eye. Naturally, this kind of adaptation arose in twilight and nocturnal insects. Ommatidia depart from sensitive cells nerve endings forming the optic nerve.

In addition to compound eyes, many insects also have simple eyes (Fig. 339), the structure of which does not correspond to the structure of one ommatidium. The refractive apparatus is lenticular in shape, immediately below it is a layer of sensitive cells. The entire eye is covered with a sheath of pigment cells. The optical properties of simple eyes are such that they cannot perceive images of objects.

Insect larvae in most cases have only simple ocelli, which, however, differ in structure from the simple ocelli of adult stages. There is no continuity between the eyes of adults and larvae. During metamorphosis, the eyes of the larvae are completely resorbed.

The visual abilities of insects are perfect. However, the structural features of the compound eye predetermine a special physiological mechanism of vision. Animals with compound eyes have "mosaic" vision. The small size of ommatidia and their isolation from each other lead to the fact that each group of sensitive cells perceives only a small and relatively narrow beam of rays. Rays incident at a significant angle are absorbed by screening pigment cells and do not reach the photosensitive elements of ommatidia. Thus, schematically, each ommatidia receives an image of only one small point of an object located in the field of view of the entire eye. As a result, the image is made up of as many light points corresponding to different parts of the object as many facets are perpendicular to the rays from the object. The overall picture is combined, as it were, from a multitude of small partial images by applying them one to another.

The perception of color by insects is also distinguished by a certain peculiarity. Representatives higher groups Insecta have color vision, based on the perception of three primary colors, the mixing of which gives all the colorful diversity of the world around us. However, in insects, compared with humans, there is a strong shift to the short-wavelength part of the spectrum: they perceive green-yellow, blue and ultra-violet rays. The latter are invisible to us. Consequently, the color perception of the world by insects differs sharply from ours.

The functions of the simple eyes of adult insects still require serious study. Apparently, they "supplement" the compound eyes to some extent, influencing the activity of the behavior of insects in different lighting conditions. In addition, simple ocelli, along with compound eyes, have been shown to be able to perceive polarized light.

The question "How many eyes do you have? common fly?" is not as simple as it seems. Two big eyes located on the sides of the head, can be seen with the naked eye. But in fact, the device of the fly's organs of vision is much more complicated.

If you look at the enlarged image of the eyes of a fly, you can see that they are similar to honeycombs and are made up of many individual segments. Each of the parts has the shape of a hexagon with regular edges. This is where the name of such an eye structure came from - facet ("facette" in French means "edge"). Many and some arthropods can boast of complex compound eyes, and the fly is far from the champion in the number of facets: it has only 4,000 facets, and dragonflies have about 30,000.

The cells we see are called ommatidia. Ommatidia are cone-shaped, the narrow end of which extends deep into the eye. The cone consists of a cell that perceives light and a lens protected by a transparent cornea. All ommatidia are closely pressed to each other and connected by the cornea. Each of them sees "their" fragment of the picture, and the brain adds these tiny images into one whole.

The location of the large compound eyes differs between female and male flies. In males, the eyes are close-set, while in females they are more spaced apart, since they have a forehead. If you look at a fly under a microscope, then in the middle of the head above the faceted organs of vision, you can see three small dots arranged in a triangle. In fact, these points are simple eyes.

In total, the fly has one pair of compound eyes and three simple ones - a total of five. Why did nature take such a difficult path? The fact is that faceted vision was formed in order to first of all cover as much space as possible with a glance and catch movement. These eyes perform the main functions. With simple eyes, the fly was "provided" to measure the level of illumination. Compound eyes are the main organ of vision, and simple eyes are secondary. If the fly did not have simple eyes, it would be slower and could only fly in bright light, and without compound eyes it would be blind.

How does a fly see the world?

Large convex eyes allow the fly to see everything around it, that is, the viewing angle is 360 degrees. It is twice as wide as a human. The fixed eyes of the insect look simultaneously on all four sides. But the visual acuity of a fly is almost 100 times lower than that of a human!

Since each ommatidium is an independent cell, the picture is reticulated, consisting of thousands of separate small images that complement each other. Therefore, the world for a fly is an assembled puzzle, consisting of several thousand pieces, and rather vague. More or less clearly, the insect sees only at a distance of 40 - 70 centimeters.

The fly is able to distinguish colors and even invisible human eye polarized light and ultraviolet. The eye of a fly senses the slightest change in the brightness of the light. She is able to see the sun hidden by thick clouds. But in the dark, flies see poorly and lead a predominantly diurnal lifestyle.

Another interesting ability of the fly is a quick reaction to movement. A fly perceives a moving object 10 times faster than a human. It easily "calculates" the speed of an object. This ability is vital for determining the distance to the source of danger and is achieved by "transferring" the image from one cell - ommatidium to another. Aeronautical engineers have adopted this feature of the fly's vision and developed a device for calculating the speed of a flying aircraft, repeating the structure of its eye.

Thanks to this fast perception, flies live in a slow-motion reality compared to us. A movement lasting a second, from a human point of view, is perceived by a fly as a ten-second action. Surely people seem to them very slow creatures. The insect brain works at the speed of a supercomputer, receiving an image, analyzing it and transmitting the appropriate commands to the body in thousandths of a second. Therefore, it is not always possible to swat a fly.

So, the correct answer to the question "How many eyes does a common fly have?" will be the number five. The main ones are a paired organ in a fly, like in many living creatures. Why did nature create exactly three simple eyes- remains a mystery.

How do insects see?

The fly abruptly dodges an object flying at it, the butterfly chooses a certain flower, and the caterpillar crawls towards itself. tall tree. Insects, like humans, also have organs of vision, but they see and perceive the world in a special way. With its exceptional vision, inaccessible to humans. Some insects can only determine light and dark, while others are well versed in shades. So how do insects see the world?

Ways to see the world in insects

Their ability to see is divided into three ways.

Whole surface of the body

Interesting feature, in which it is not necessary to have eyes. But its big disadvantage is that the insect can only distinguish light from darkness. It does not see any objects or flowers. How does it work? Light passes through the cuticle outer layer skin, and penetrates to the head of the insect. There, a reaction takes place in the brain cells, and the insect understands that light is falling on it. Such a device is not available to everyone, but it helps a lot those insects that live underground, for example, earthworms or blind cave beetles. This type of vision is found in cockroaches, aphids and caterpillars.

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With simple eyes

Insects with simple eyes are more fortunate. They can not only determine darkness from light, but also distinguish between individual objects and even their shape. Such eyes are most often found in insect larvae. For example, mosquito larvae have eyes instead of dark spots that capture light. But the caterpillars have five to six eyes on each side of the head. Because of this, she is well versed in forms. But she sees vertical objects much better than horizontal ones. For example, if she has to choose a tree, then she will rather crawl to the one that is higher, and not to the one that is wider.

Compound or faceted eyes

Such eyes are most often found in adult insects. You can immediately identify them - they are usually located on the sides of the head. Compound eyes are much more complex and diverse than all the others. They can recognize the shapes of objects and identify colors. Some insects see well during the day, while others see well at night. An interesting feature of these eyes is that they do not see the whole picture as a whole, but only pieces. And already in the brain, the insect collects a puzzle from the received images in order to see complete picture. How does the fly manage to connect all the pieces of the fragment in flight? Surprisingly, it is in flight that she sees better than at rest. And for a landing site, any insect is more likely to choose something that moves or sways.

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Varieties of the structure of the organs of vision

In insects, the eyes can be represented in three varieties:

(faceted);
(dorsal, ocelli);
larval (lateral, larval). (a photo)

They have different structure and unequal ability to see.

Compound eyes are found in most insects, and the more highly developed the latter, the better their organs of vision are usually developed. also called faceted because they outside surface It is represented by a set of lenses located next to each other - facets.

Ommatidium

A (left) - appositional ommatidium,

B (right) - superpositional ommatidium

1 - axons of visual cells, 2 - retinular cells,

3 - cornea, 4 - crystalline cone,

5 - pigment cells, 6 - light guide, 7 - rhabdom

The compound eye is composed of various a large number individual structural units- ommatidians. include a number of structures that provide conduction, light refraction (facet, root cell, crystal cone) and perception of visual signals (retinal cells, rhabdom, nerve cells). In addition, each has a pigment isolation device, due to which it is completely or partially protected from lateral rays.

Diagram of the structure of a simple eye

Of all the varieties of insect eyes, they have the weakest ability to see. According to some reports, they do not perform a visual function at all, and are only responsible for improving the function of compound eyes. This, in particular, is proved by the fact that in insects there are practically no simple ones in the absence of complex ones. In addition, when painting over compound eyes, insects cease to orient themselves in space, even if they have well-defined ones.

Features of insect vision

Dedicated to the study of insect vision great amount scientific works. In view of such interest on the part of specialists, many features of the work of the eyes in Insecta have been reliably elucidated to date. However, the structure of the organs of vision in these organisms is so diverse that the quality of vision, the perception of color and volume, the distinction between moving and stationary objects, the recognition of familiar visual images, and other properties of vision differ enormously in different groups insects. The following factors can influence this: compound eye- structure of ommatidia and their number, bulge, location and shape of the eyes; in simple eyes and - their number and subtle features of the structure, which can be represented by a significant variety of options. The vision of bees has been best studied today.

A certain role in the perception of form is played by the movement of the object. Insects are more likely to sit on flowers that sway in the wind than on stationary ones. dragonflies rush after moving prey, and male butterflies react to flying females and have trouble seeing sitting ones. Probably, the matter is in a certain frequency of irritation of the ommatidia eyes during movement, flashing and flickering.

Recognition of familiar objects

Insects recognize familiar objects not only by color and shape, but also by the arrangement of objects around them, so the idea of \u200b\u200bthe exceptional primitiveness of their vision cannot be called true. For example, the Sand Wasp finds the entrance to the mink, focusing on those objects that are located around it (grass, stones). If they are removed or their location changed, this can confuse the insect.

distance perception

This feature is best studied on the example of dragonflies, ground beetles and other predatory insects.

The ability to determine the distance is due to the presence in higher insects binocular vision, that is, two eyes whose fields of view partially intersect. The structural features of the eyes determine how large the distance available for the review of an insect is. For example, jumping beetles react to prey and pounce on it when they are at a distance of 15 cm from the object.

Light compass movement

Many insects move in such a way that they constantly maintain the same angle of incidence of light on the retina. In this way, Sun rays are a kind of compass by which the insect is oriented. By the same principle, moths move in the direction of artificial light sources.