The structure of an earthworm. Earthworm: lifestyle, habitat and benefits for the soil Organs of the circulatory system of the earthworm

Behind the mouth opening is a strong muscular pharynx, passing into a thin esophagus, and then into an extensive goiter. In the goiter, food accumulates and is wetted. After that, it enters the muscular chewing stomach, which looks like a bag with thick solid walls. Here the food is ground, after which, by contraction of the muscular walls of the stomach, it moves into a thin tube - the intestine. Here, under the action of digestive juices, food is digested, nutrients are absorbed through the intestinal wall into the body cavity and enter the bloodstream. With blood, nutrients are carried throughout the body of the worm. Undigested food remains are thrown out through the anus.

excretory organs

The excretory organs of the worm consist of the thinnest whitish convoluted tubules. They lie in pairs in almost every segment of the body of the worm. Each tube at one end opens with a funnel-shaped extension into the body cavity. The other end opens outwards on the ventral side of the animal with a very small opening. Through these tubes, unnecessary substances accumulating there are released from the body cavity.

Nervous system

The nervous system of earthworm more difficult than the hydra. It is located on the ventral side of the body and looks like a long chain - this is the so-called ventral nerve cord. Each segment of the body has one double ganglion. All nodes are interconnected by jumpers. At the anterior end of the body in the pharynx, two jumpers depart from the nerve chain. They cover the pharynx on the right and left, forming a peripharyngeal nerve ring. There is a thickening on top of the peripharyngeal ring. This is the supraesophageal ganglion. From it to the front, part of the body of the worm departs a lot of the finest nerves. This explains the great sensitivity of this part of the body. This feature of the structure of the earthworm has a protective value. Branching through the tissues and organs of the body, the nervous system of the earthworm and other animals regulates and integrates the activity of all organs, connecting them into one whole - the body of the animal.

body symmetry

Unlike the hydra and many other coelenterates, the body of the earthworm has a clearly pronounced bilateral symmetry of the body. In animals with such a structure, the body is divided into two identical halves, right and left - the only plane of symmetry that can be drawn along the main axis of the body from the mouth to the anus. Bilateral symmetry is characteristic of worms and many other animals.

The transition of worms from the radial radial symmetry of the body, characteristic of their ancestors - intestinal, to bilateral symmetry is explained by their transition from a floating or sedentary lifestyle to crawling, to a terrestrial lifestyle. Consequently, the development of different forms of symmetry in multicellular animals is associated with a change in the conditions of their existence.

The internal structure can be clearly seen when opening the worm.

Before opening, the worm is killed by immersing it in dilute alcohol (10%) for several minutes. Then the worm is placed in the dissecting bath with its back up (a red blood vessel is clearly visible along its back), two pairs of pins are pinned at the front and rear ends of the body to the bottom of the dissecting bath, and then, starting from the back end, they are made either with thin scissors or with a blade razor longitudinal incision of the skin-muscular sac, keeping slightly to the right of the midline (so as not to damage the translucent blood vessel).

Then the cut walls of the body are deployed on both sides, they are fixed with several pairs of pins and water is poured so that it covers the opened worm (then its internal structure will be more clearly visible).

On the opened worm, first of all, the body cavity is visible, in which various internal organs lie. Thin transverse partitions divide the body cavity into separate chambers corresponding to the external division of the body into segments (Fig. 89).

Of the internal organs, the straight and voluminous intestines, which run along the entire length of the body, are most clearly visible. It consists of several sections: from a small oral cavity, followed by a muscular pharynx, then passing into a narrow esophagus, leading first to the goiter, then to the muscular stomach, in which the food is rubbed, and finally to the long intestine, which stretches to the rear end of the body and ends in the anus, or anus, opening.

Vessels of the circulatory system are visible above the intestines; they are clearly visible in the earthworm, because its blood is red (recall that in lower worms, and even more so in bilayer animals, we do not find a circulatory system). A large dorsal vessel runs along the entire intestine from above.

In the anterior part of the body, clearly visible paired branches depart from the spinal vessel, which, like hoops, wrap around the esophagus and connect the dorsal vessel to the abdominal vessel, which runs along the body already under the intestines. These several pairs of vessels are called "hearts" because their muscular walls force the blood to move through the vascular system with their contractions.

Through the dorsal vessel, blood flows from the posterior end of the body to the anterior part, then through the "hearts" it passes into the abdominal vessel and here it flows already in reverse direction, that is, to the posterior end of the body.

In addition to these main vessels, the worm has even finer vessels; some of them, like "hearts", encircle the intestines, others go to various organs of the body.

The circulatory system brings to the tissues of the body the substances they need - the nutrient material that enters the blood from the intestines, and oxygen - and takes away the decay products from them - carbon dioxide and nitrogenous substances.

The excretory system of an earthworm has the appearance of small white convoluted tubes adjacent to those partitions that divide the body cavity into separate segments. One end of each such tube opens in the form of a small funnel into the body cavity, the other end opens outward. Since these excretory tubules (nephridia) are distributed in pairs among individual segments, or segments, of the body, they are also called segmental organs.

The worm does not have a special respiratory system, and its gas exchange occurs through the entire surface of the body, dressed in a thin and always wet cuticle. Respiratory gas exchange takes place in moist soil, where it penetrates and atmospheric air. In rainy weather, when the soil is saturated with water with a high content of carbon dioxide (released during the decomposition of humus), earthworms feel a lack of oxygen, and this causes them to come to the surface.

The nervous system of the earthworm forms a peripharyngeal ring in the anterior part of the body, consisting of the supraesophageal node, or “brain”, of a pair of nerve cords covering the pharynx on both sides, and of the subpharyngeal node, located already under the intestines.

The subpharyngeal node begins the abdominal nerve chain, which stretches along the lower wall of the body (to see it, you need to remove the intestines). The abdominal chain consists of nerve nodes - one node for each segment of the body - and of the nerve cords connecting them. All these nodes are double, that is, each was formed from a pair of nodes merged with each other, and nerves depart from each node to neighboring organs.

Thus, each ganglion is a special nerve center for its segment, but they all act in concert, depending on the activity of the supraesophageal ganglion, which is therefore called the "brain" of the worm.

Closer to the anterior end of the worm at the bottom of the body cavity are the reproductive organs. Earthworms are bisexual animals, or hermaphrodites, that is, each of them has both male and female reproductive organs - both testes and ovaries. Both testes and ovaries open with separate paired openings on the ventral side of the body.

In the structure of the body of an earthworm, one feature clearly stands out: its entire body is divided into segments that go one after another, which seem to repeat each other with their structure.

Outside, the segments are separated by intercepts and have the form of rings with eight bristles on each ring, and inside each intercept corresponds to a transverse septum and each segment has its own paired ganglion, its own pair of transverse blood vessels encircling the intestines, its own pair of excretory tubes, its own annular and longitudinal muscles. Such a structure, when repeating, almost identical parts go one after another in the body, is called metameric (Fig. 89, 91).

The body of an earthworm is distinguished by a round shape, most representatives of this genus are no more than 15 centimeters long, sometimes more than twenty, and the length of the largest is a little over thirty centimeters.

Consists of 100-180 segments. On the segments there is a small rather elastic bristle, which is practically invisible, but if you run your finger from the back tip to the front, you can immediately feel it. The bristles are needed by the worm in order to cling to the ground irregularities during movement.

On the front of the body of the worm there is a small thickening that serves as a place in which the genitals are located. The cells located in this thickening are activated during reproduction for laying eggs. If you look closely, you can see that the stomach of the earthworm is somewhat lighter than the rest of the parts. The worm has not only a circulatory system, but also a nervous, tactile system, as well as a digestive system.

What environment do earthworms live in?

In the daytime, worms prefer to stay in the soil of the swarm in it. Light soil, the worm drills with its front tip. To do this, he first compresses the front part, so that it becomes thinner, and tries to push it forward between soil lumps. Subsequently, the front tip becomes thicker, the lumps move apart, and the worm pulls the back. In hard ground, raincoats make their way, passing it through the intestinal tract. Earthen heaps are often visible on the surface of the earth; these are traces of the nocturnal activity of worms. From their minks, they get out after heavy rainfall (therefore they are called - rain). In the summer, worms prefer to stay in upper layers soil, and in winter, fleeing from the cold, they dig holes, the depth of which can be more than two meters.

With a decrease in temperature, they become less active, and their circulatory system circulates more slowly.

Taking the worm in hand, you can find that its skin is moist, and it is covered with mucus, which makes it easier to move in the ground. Apart from this, only through a moist skin, the oxygen required for breathing is in his body. This is how the worm breathes.

Directly under the skin are circular muscles fused with it, under them are longitudinal. Those. The earthworm is a kind of musculocutaneous sac. Thanks to the circular muscles, the body of the worm becomes thinner and longer, and thanks to the longitudinal muscles, it is shortened and thickened. Due to the alternate functioning of these muscles and the worm, it moves.

How does an earthworm work

The structure of the earthworm, when compared with the organisms of other animals, is quite primitive, but it has quite interesting features. Under the musculocutaneous sac is a fluid-filled cavity of the body, and it contains the internal organs. When compared with worms belonging to the round species, the body cavity of the roundworm is divided by partitions, the number of which is equal to the number of segments. They have their own separate walls and are located under the musculocutaneous sac.

Now let's take a closer look at all the available organs of the worm.

Digestive system

The mouth of the earthworm is in front. There is a raincoat prefers rotting vegetation, swallowing it with soil. In the same way, he often drags fallen leaves into his mink. Swallowing is done through the pharynx. Next, the food is in the intestines. Food that has not had time to be digested comes out through the anus located behind. This is how the digestive system works in almost all types of worms. The mouth of the worm is also necessary in order to drag various small objects to which it simply sticks. As you can see, the digestive system is quite primitive and lacks the organs that higher beings have.

The earthworm has a closed circulatory system, but there are some features. It is based on two main vessels, the dorsal and abdominal, which are interconnected by means of annular vessels, in some ways very similar to arteries and veins. Depending on the species, the blood of worms can be colorless, red, or even green.

Speaking about the circulatory system of the earthworm, the dorsal vessel deserves special attention, which pulsatingly drives blood through the body.

Special vessels that cover the intestines and are located in all segments distill blood into the cavity of the abdominal vessel, which cannot pulsate on its own. Blood flow in the worm from front to back. In addition to these blood flows, there are also vessels that carry blood from the spinal to the parapodial vessels. In them, the blood is oxidized, in contact with the oxygen of the environment.

The skin of an annelids also has its own vessels, which are connected to the general circulatory system. Those. the circulatory system of worms is quite complex, but it is thanks to it that worms survive in rather difficult conditions.

Nervous system

The nervous system of annelids is represented by two nerve trunks. In the segment on them, nerve nodes are formed. those. a kind of nerve circuit emerges. In front, two nodules are interconnected by circular bridges - a perioral nerve ring is obtained. Nerves run from the nodules to various organs.

sense organs

Worms do not have special organs of touch, however, sensitive cells in the skin enable it to feel touched and distinguish when it is light and when it is dark.

reproductive system

As you know, and we have already talked about this, worms are hermaphrodites, that is, they can do without mating. But most often, after all, reproduction occurs after the contact of two individuals and the exchange of sperm between them. Then they spread, and mucus begins to stand out from a kind of clutch located in front. In which the eggs subsequently enter. Then a lump of mucus slides off the body of the worm, forming a cocoon. From which small worms are subsequently obtained.

This video talks about the structural features of earthworms.

Well known to all earthworms constitute a large group of species belonging to different families of oligochaetes.

Our common earthworm, reaching 30 centimeters in length and a centimeter in thickness, belongs to the most fully studied family of Lumbricidae, which includes about 200 species, about a hundred of which are found in Russia.

Types of earthworms

According to the characteristics of the biology of earthworms, earthworms can be divided into two types: the first includes worms that feed on the surface of the soil, the second - those that feed in the soil. In the first type, litter worms can also be distinguished, which live in the litter layer and under no circumstances (even when the soil dries out or freezes) do not sink into the ground deeper than 5-10 centimeters. This type also includes soil-litter worms that penetrate the soil deeper than 10-20 centimeters, but only under unfavorable conditions, and burrowing worms that make constant deep passages (up to 1 meter or more), which they usually do not leave, but when feeding and mating, only the front end of the body protrudes to the surface of the soil. The second type can be divided into burrowing worms, living in the deep soil horizon, and burrowing worms, which have constant moves, but feed in the humus horizon.

Litter and burrowing worms inhabit places with waterlogged soils - the banks of water bodies, swampy soils, soils of humid subtropics. In the tundra and taiga, only litter and soil-litter forms live, and in the steppes, only soil forms proper. They feel best in conditions of coniferous-deciduous forests: all types of Lumbricidae live in these zones.

Lifestyle of worms

According to the way of life, worms are nocturnal animals, and at night you can observe how they swarm everywhere in large numbers, while remaining with their tails in minks. Stretching out, they rummage around the surrounding space, grab with their mouths (at the same time, the pharynx of the worm turns slightly outward and then retracts back) damp fallen leaves and drag them into minks.

Earthworms are omnivores. They swallow a huge amount of earth, from which they assimilate organic matter, in the same way they eat a large number of all kinds of half-decayed leaves, with the exception of very hard or having an unpleasant smell for them. When keeping worms in pots of earth, you can watch them eat fresh leaves some plants.

Very interesting observations of earthworms were made by C. Darwin, who devoted a large study to these animals. In 1881, his book "The Formation of the Vegetative Layer by the Activity of Earthworms" was published. Charles Darwin kept earthworms in pots of earth and conducted interesting experiments to study the nutrition and behavior of these animals. So, in order to find out what kind of food, besides leaves and earth, worms can eat, he pinned pieces of boiled and raw meat on the surface of the earth in a pot and watched how every night the worms pulled the meat, and most of the pieces were eaten. They also ate pieces of dead worms, for which Darwin even called them cannibals.

Half-rotted or fresh leaves are dragged by worms through the holes of minks to a depth of 6-10 centimeters and eaten there. Darwin observed how worms capture food items. If to the surface of the earth flower pot pin fresh leaves, then the worms will try to drag them to their minks. Usually they tear off small pieces, grabbing the edge of the leaf between the prominent upper and lower lip. At this time, a thick, powerful pharynx protrudes forward and thereby creates a fulcrum for the upper lip. If the worm comes across a flat, large surface of a leaf, it acts differently. The anterior rings of the body are slightly drawn into the subsequent rings, due to which the anterior end of the body expands, becomes blunt with a small hole at the end. The pharynx moves forward, is pressed against the surface of the sheet, and then, without detaching, is pulled back and slightly expanded. As a result, a "vacuum" is formed in the hole at the front end of the body, applied to the leaf. The pharynx acts like a piston, and the worm sticks very firmly to the surface of the leaf. If you put a thin fading cabbage leaf on the worm, then with reverse side from the worm you can see a depression just above the head end of the animal. The worm never touches the veins of the leaf, but sucks out the delicate tissues of the leaves.

Worms use the leaves not only for food, but also plug the entrances to the minks with them. To this end, they also drag pieces of stems, withered flowers, scraps of paper, feathers, and tufts of wool into holes. Sometimes bundles of leaf petioles or feathers protrude from the worm's hole.

Leaves dragged into the burrows of worms are always crumpled or folded into a large number of folds. When the next leaf is pulled in, it is placed on the outside of the previous one, all the leaves are tightly folded and pressed against each other. Sometimes the worm enlarges the hole of its mink or makes another next to it in order to collect even more leaves. The worms fill the gaps between the leaves with moist earth thrown out of their intestines in such a way that the minks are completely clogged. Such clogged minks are especially common in the autumn before the wintering of the worms. The upper part of the passage is lined with leaves, which, according to Darwin, prevents the worm's body from contacting the cold and wet ground near the soil surface.

Darwin also described how earthworms dig holes. They do this either by pushing the earth in all directions, or by swallowing it. In the first case, the worm pushes the narrow front end of the body into the gaps between the particles of the earth, then inflates and contracts it, and thereby the soil particles move apart. The front end of the body works like a wedge. If the earth or sand is very dense, compacted, the worm cannot push the soil particles apart and acts in a different way. It swallows the earth, and, passing it through itself, gradually sinks into the ground, leaving behind a growing pile of excrement. The ability to absorb sand, chalk or other substrates completely devoid of organic matter is a necessary adaptation in the event that the worm, plunging into the soil from excessive dryness or cold, finds itself in front of unbroken dense layers of soil.

Minks of worms go either vertically or a little sideways. Almost always they are lined from the inside with a thin layer of black earth processed by animals. Lumps of earth ejected from the intestines are compacted along the walls of the mink by the vertical movements of the worm. The lining thus formed becomes very hard and smooth and closely adheres to the body of the worm, and the setae curved back have excellent points of support, which allows the worm to move forward and backward very quickly in the hole. The lining, on the one hand, strengthens the walls of the mink, on the other hand, protects the body of the worm from scratches. Minks leading down usually end with an extension, or a chamber. Here the worms spend the winter, singly or weaving into a ball of several individuals. The mink is usually lined with small stones or seeds, which creates a layer of air for the worms to breathe.

After the worm swallows a portion of the earth, whether it is done for food or for digging a passage, it rises to the surface to throw the earth out of itself. The discarded earth is saturated with intestinal secretions and, as a result, becomes viscous. After drying, lumps of excrement harden. The earth is thrown out by the worm not randomly, but alternately in different sides from the entrance to the hole. The tail works like a shovel. As a result, a kind of tower of excrement lumps is formed around the entrance to the burrow. Such turrets in worms different types have different shape and height.

Earthworm exit

When the worm protrudes from the mink to throw out excrement, it stretches its tail forward, but if it is to collect leaves, it puts out its head. Therefore, worms have the ability to roll over in their burrows. Worms do not always throw excrement on the surface of the soil. If they find some kind of cavity, for example, near the roots of trees, in newly dug up earth, they deposit their excrement there. It is easy to see that the space under stones or fallen tree trunks is always filled with small pellets of earthworm excrement. Sometimes animals fill the cavities of their old minks with them.

Life of earthworms

Earthworms in the history of the formation of the earth's crust played a much more important role than it might seem at first glance. They are numerous in almost all humid areas. Due to the digging activity of the worms, the surface layer of the soil is in constant motion. As a result of this “digging”, soil particles are rubbed against each other, new layers of soil brought to the surface are exposed to carbon dioxide and humic acids, which contributes to the dissolution of many minerals. The formation of humic acids is due to the digestion of semi-decomposed leaves by earthworms. It has been established that worms contribute to an increase in the content of phosphorus and potassium in the soil. In addition, passing through the intestinal tract of worms, earth and plant residues stick together with calcite, a derivative of calcium carbonate secreted by calcareous glands. digestive system worms. The excrement compressed by contractions of the intestinal muscles is thrown out in the form of very strong particles, which are washed out much more slowly than simple lumps of earth of the same size and are elements of the granular structure of the soil. The amount and mass of excrement produced annually by earthworms is enormous. During the day, each worm passes through its intestines an amount of earth approximately equal to the weight of its body, i.e. 4-5 grams. Every year, earthworms throw a layer of excrement 0.5 cm thick onto the surface of the earth. C. Darwin counted them up to 4 tons of dry matter per hectare of pastures in England. Near Moscow, in a field of perennial grasses, earthworms annually form 53 tons of excrement per hectare of land.

Worms the best way they prepare the soil for the growth of plants: they loosen it so that there is no lump larger than they can swallow, they facilitate the penetration of water and air into the soil. Dragging the leaves into their burrows, they crush them, partially digest them and mix them with earthen excrement. Evenly mixing the soil and plant residues, they prepare a fertile mixture, like a gardener. The roots of plants move freely in the soil along the paths of earthworms, finding rich nutritious humus in them. It is impossible not to be surprised when you think that the entire fertile layer has already passed through the bodies of earthworms and will pass through them again in a few years. It is doubtful, Darwin believes, that there are still other animals that would occupy such a prominent place in the history of the earth's crust as these essentially lowly organized creatures.

Thanks to the activity of worms, large objects, stones gradually sink deep into the earth, and small fragments of stones are gradually ground in their intestines to sand. Darwin, describing how abandoned castles in old England were gradually sinking underground, emphasized that archaeologists should be indebted to earthworms for the preservation of a large number of ancient objects. After all, coins, gold jewelry, stone tools, etc., falling on the surface of the earth, are buried under the excrement of worms for several years and are thus reliably preserved until the earth covering them is removed in the future.

Earthworms, like many other animals, are affected by human activities. Their numbers are declining due to the excessive use of fertilizers and pesticides, cutting down of trees and shrubs, under the influence of overgrazing of livestock. 11 species of earthworms are included in the Red Book of the Russian Federation. Successful attempts have been repeatedly made to relocate and acclimatize worms of different species to those areas where they are not enough. Such activities are called zoological reclamation.

Animals, suborder earthworms. The body of an earthworm consists of annular segments, the number of segments can reach up to 320. When moving, earthworms rely on short bristles that are located on the body segments. When studying the structure of an earthworm, it is clear that, unlike the whipworm, its body looks like a long tube. Earthworms are distributed throughout the planet, except for Antarctica.

Appearance

Adult earthworms are 15 - 30 cm in length. In the south of Ukraine, it can reach large sizes. The body of the worm is smooth, slippery, has a cylindrical shape and consists of piece rings - segments. This form of the body of the worm is explained by the way of its life, it facilitates movement in the soil. The number of segments can reach 200. The ventral side of the body is flat, the dorsal side is convex and darker than the ventral side. Approximately where the front of the body ends, the worm has a thickening called a girdle. It contains special glands that secrete a sticky liquid. During reproduction, an egg cocoon is formed from it, inside which the eggs of the worm develop.

Lifestyle

If you go out into the garden after rain, you can usually see small piles of earth thrown out by earthworms on the path. Often at the same time, the worms themselves crawl along the path. It is because they appear on the surface of the earth after rain that they are called rain. These worms crawl out to the surface of the earth also at night. The earthworm usually lives in humus-rich soil and is not common in sandy soils. He also does not live in swamps. Such features of its distribution are explained by the way of breathing. The earthworm breathes on the entire surface of the body, which is covered with mucous, moist skin. Too little air is dissolved in the water, and therefore the earthworm suffocates there. He dies even faster in dry soil: his skin dries up, and breathing stops. In warm and humid weather, earthworms stay closer to the surface of the earth. During a prolonged drought, as well as during a cold period, they crawl deep into the ground.

moving

The earthworm moves by crawling. At the same time, it first draws in the anterior end of the body and clings with the bristles located on the ventral side to the unevenness of the soil, and then, contracting the muscles, pulls up the posterior end of the body. Moving underground, the worm makes its own passages in the soil. At the same time, he pushes the earth apart with the pointed end of the body and squeezes between its particles.

Moving in dense soil, the worm swallows the earth and passes it through the intestines. The worm usually swallows the earth at a considerable depth, and throws it out through the anus at its mink. So on the surface of the earth long "laces" of earth and lumps are formed, which can be seen in the summer on garden paths.

This method of movement is possible only in the presence of well-developed muscles. Compared to the hydra, the earthworm has more complex musculature. She lies under his skin. Muscles together with the skin form a continuous musculocutaneous sac.

The muscles of the earthworm are arranged in two layers. Beneath the skin lies a layer of circular muscles, and beneath them is a thicker layer of longitudinal muscles. Muscles are made up of long contractile fibers. With the contraction of the longitudinal muscles, the body of the worm becomes shorter and thicker. When the circular muscles contract, on the contrary, the body becomes thinner and longer. Contracting alternately, both layers of muscles cause the movement of the worm. Muscle contraction occurs under the influence nervous system branching in muscle tissue. The movement of the worm is greatly facilitated by the fact that there are small bristles on its body from the ventral side. They can be felt by running a finger dipped in water along the sides and along the ventral side of the worm's body, from the rear end to the front. With the help of these bristles, the earthworm moves underground. With them, he lingers when he is pulled out of the ground. With the help of bristles, the worm descends and rises along its earthen passages.

Nutrition

Earthworms feed mainly on half-decayed plant remains. They drag, usually at night, leaves, stems and other things into their minks. Earthworms also feed on humus-rich soil, passing it through their intestines.

Circulatory system

The earthworm has a circulatory system that the hydra does not have. This system consists of two longitudinal vessels - dorsal and abdominal - and branches that connect these vessels and carry blood. The muscular walls of the vessels, contracting, drive blood throughout the body of the worm.

The blood of an earthworm is red, it has a very importance. With the help of blood, the connection between the organs of the animal is established, metabolism occurs. Moving through the body, it carries nutrients from the digestive organs, as well as oxygen entering through the skin. At the same time, the blood carries carbon dioxide out of the tissues into the skin. Various unnecessary and harmful substances formed in all parts of the body, together with the blood, enter the excretory organs.

Irritation

The earthworm does not have special sense organs. He perceives external stimuli with the help of the nervous system. The earthworm has the most developed sense of touch. Sensitive tactile nerve cells are located all over the surface of his body. The sensitivity of the earthworm to various kinds of external irritation is quite high. The slightest vibrations of the soil make him quickly hide, crawling into a mink or into deeper layers of soil.

The value of sensitive skin cells is not limited to touch. It is known that earthworms, having no special organs of vision, still perceive light stimuli. If at night you suddenly illuminate the worm with a lantern, it quickly hides.

The response of an animal to stimulation, carried out with the help of the nervous system, is called a reflex. There are different types of reflexes. The contraction of the body of the worm from touch, its movement when suddenly illuminated by a lantern, has a protective value. This is a protective reflex. Grabbing food is a digestive reflex.

Experiments also show that earthworms smell. The sense of smell helps the worm find food. Charles Darwin also established that earthworms can smell the leaves of the plants they feed on.

reproduction

Unlike the hydra, the earthworm reproduces exclusively sexually. It does not have asexual reproduction. Each earthworm has male organs - the testes, in which the gums develop, and the female genital organs - the ovaries, in which the eggs are formed. The worm lays its eggs in a slimy cocoon. It is formed from a substance secreted by the girdle of the worm. In the form of a clutch, the cocoon slides off the worm and is pulled together at the ends. In this form, the cocoon remains in the earthen burrow until young worms emerge from it. The cocoon protects the eggs from moisture and other adverse effects. Each egg in the cocoon divides many times, as a result of which tissues and organs of the animal are gradually formed, and, finally, small worms similar to adults emerge from the cocoons.

Regeneration

Like hydras, earthworms are capable of regeneration, in which lost parts of the body are restored.