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

The organs of vision are developed in most insects. The greatest development is achieved 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 ommatidia consists of a transparent lens, or cornea, in the form of a biconvex lens and an underlying transparent crystal cone. Together they make up optical system. Under the cone is the retina, which perceives light rays. Retinal cells connected nerve fibers with the optic lobes of the brain. Each ommatidium is surrounded by pigment cells.

Depending on the perception of light varying intensity There are appositional and superpositional types of eyes. The first type of eye structure is characteristic of diurnal insects, the second - nocturnal.

IN apposition eye each ommatidia 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” part of the external space. The overall picture is formed in the insect’s brain as if from many pieces of a mosaic.

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

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

Of all the types of insect eyes, simple ocelli 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 the compound eyes. This, in particular, is proven by the fact that insects practically do not have simple eyes in the absence of complex ones. In addition, when compound eyes are painted over, insects cease to orient themselves in space, even if they have well-defined simple eyes.

Stemmas, or lateral simple eyes– present in insect larvae with complete metamorphosis. During the pupal stage, they "morph" into compound eyes. They perform a visual function, but, due to their simplified structure, they see relatively poorly. To improve vision, larval eyes are often present in several pieces. In sawfly larvae they are similar to the dorsal ones, and in butterfly caterpillars they resemble the ommatidia of the compound eye. Caterpillars perceive the shape of objects and 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 complex faceted eyes of approximately the same structure as the complex eyes of crustaceans.

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

Each ommatidium represents a perfect photooptic 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 perceptive apparatus of the ommatidia is represented by several (4 - 12) receptor cells; their specialization has gone very far, as evidenced by their complete loss of flagellar structures. The actual 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 - rhabdom.

Shielding pigment cells lie along the edges of the ommatidium; the latter differ quite significantly between diurnal and nocturnal insects. In the first case, the pigment in the cell is motionless and constantly separates neighboring ommatidia, preventing light rays from passing from one eye to the other. In the second case, the pigment is able to move in the cells and accumulate only in their upper part. In this case, the light rays hit the sensitive cells of not one, but several neighboring ommatidia, which significantly (almost two orders of magnitude) increases the overall sensitivity of the eye. Naturally, this kind of adaptation arose in twilight and nocturnal insects. Ommatidia originate from sensory cells nerve endings forming the optic nerve.

In addition to compound eyes, many insects also have simple ocelli (Fig. 339), the structure of which does not correspond to the structure of a single ommatidium. The light-refracting apparatus is lens-shaped; immediately below it is a layer of sensitive cells. The entire eye is covered with a cover 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 differ, however, in structure from the simple ocelli of the adult stages. There is no continuity between the ocelli 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 shielding pigment cells and do not reach the photosensitive elements of the 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 composed of as many light points corresponding to different parts of the object as the number of facets the rays from the object fall perpendicularly to. The overall picture is combined, as it were, from many small partial images by applying them one to another.

The perception of color by insects is also distinguished by a certain originality. 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 to humans, there is a strong shift to the short-wave 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 is sharply different from ours.

The functions of simple eyes of adult insects still require serious study. Apparently, they to some extent “supplement” the compound eyes, influencing the activity and behavior of insects in different lighting conditions. In addition, it has been shown that simple ocelli, along with compound eyes, are capable of perceiving polarized light.

The question "How many eyes does 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 reality, the structure of the fly's visual organs is much more complex.

If you look at a magnified view of a fly's eyes, you can see that they are honeycomb-like and made up of many individual segments. Each part has the shape of a hexagon with regular edges. This is where the name for this eye structure comes from – facet (“facette” translated from French means “edge”). Many arthropods can boast of complex faceted eyes, and the fly is far from holding the record for the number of facets: it has only 4,000 facets, while dragonflies have about 30,000.

The cells we see are called ommatidia. Ommatidia have a cone-shaped shape, 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 puts these tiny images into one whole.

The arrangement of the large compound eyes is different in female and male flies. In males, the eyes are set close together, 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 facet 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 - five in total. Why did nature take such a difficult path? The fact is that facet vision formed to primarily cover as much space as possible with the gaze and capture movement. Such eyes perform basic 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 a secondary organ. If a fly did not have simple eyes, it would be slower and could only fly in bright light, and without compound eyes it would go blind.

How does a fly see the world around it?

Large, convex eyes allow the fly to see everything around it, that is, the visual angle is 360 degrees. This is twice as wide as a human's. The insect's motionless eyes simultaneously look in all four directions. But the visual acuity of a fly is almost 100 times lower than that of a human!

Since each ommatidia is an independent cell, the picture turns out to be a mesh, consisting of thousands of individual small images that complement each other. Therefore, for a fly, the world is an assembled puzzle consisting of several thousand pieces, and a rather vague one at that. The insect sees more or less clearly at only a distance of 40 - 70 centimeters.

The fly is able to distinguish colors and even invisible to the human eye polarized light and ultraviolet. The fly's eye senses the slightest changes in the brightness of 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 a fly is its 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 “transmitting” the image from one cell - the ommatidia - to another. Aviation engineers took advantage of 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 such fast perception, flies live in a slower reality compared to us. A movement that lasts a second, from a human point of view, is perceived by a fly as a ten-second action. Surely people seem to them to be very slow creatures. The insect's 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 an ordinary fly have?” the number will be five. The main ones are a paired organ in the fly, as in many living beings. Why did nature create exactly three simple eyes- remains a mystery.

How do insects see?

A fly sharply dodges an object flying at it, a butterfly chooses a certain flower, and a caterpillar crawls towards the very tall tree. Insects, like people, also have visual organs, but they see and perceive the world in a special way. With his 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?

Insects' ways of seeing the world

Their ability to see is divided into three ways.

Whole body surface

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 colors. How does it work? Light passes through the cuticle outer layer skin and penetrates the insect's head. There a reaction occurs in the brain cells, and the insect understands that light is falling on it. Such a device is not available to everyone, but it is very helpful for 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 luckier. 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 eyes. dark spots that catch light. But caterpillars have five to six eyes on each side of their heads. Thanks to 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, she will rather crawl to the one that is taller than to the one that is wider.

Compound or compound eyes

Such eyes are most often found in adult insects. You can identify them immediately - they are usually located on the sides of the head. Compounded eyes are much more complex and varied 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 assembles a puzzle from the received images in order to see full picture. How does a fly manage to connect all the pieces of a 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, eyes can be presented in three varieties:

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

They have different structure and unequal ability to see.

Compound eyes are found in most insects, and the more highly developed the latter are, the better their visual organs 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) - superposition ommatidium

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

3 - cornea, 4 - crystalline cone,

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

The compound eye consists of various, usually large quantity individual structural units- ommatidia. include a number of structures that provide conduction, refraction of light (facet, corneal cells, crystalline cone) and perception of visual signals (retinal cells, rhabdom, nerve cells). In addition, each has a pigment insulation device, due to which it is fully or partially protected from side rays.

Diagram of the structure of a simple eye

Of all types of eyes, insects 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 the compound eyes. This, in particular, is proven by the fact that in insects there are practically no simple ones without complex ones. In addition, when the compound eyes are painted over, insects cease to orient themselves in space, even if they have well-defined eyes.

Features of insect vision

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

The movement of an object plays a certain role in the perception of shape. Insects are more likely to land 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. This is probably due to a certain frequency of irritation of the ommatidia of the eyes during movement, flickering and flickering.

Recognizing 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 the exceptional primitiveness of their vision cannot be called true. For example, the Sand Wasp finds the entrance to a burrow, guided by the objects that are located around it (grass, stones). If they are removed or their location is changed, this can confuse the insect.

Perception of distance

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

The ability to determine distance is due to the presence of higher insects binocular vision, that is, two eyes whose fields of vision partially intersect. The structural features of the eyes determine how large the viewing distance of a particular 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.

Luminous movement

Many insects move in such a way that they constantly maintain the same angle of incidence of light on the retina. Thus, 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.