The structure of the earthworm. The structure of the body and the main vital functions of earthworms

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 through the intestinal wall nutrients are absorbed 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, nervous system earthworm and other animals regulates and unites 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. Therefore, development in multicellular animals different forms symmetry is associated with a change in the conditions of their existence.

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 not only has circulatory system, but also nervous, tactile is also 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 pave their way, passing it through 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 summer, worms prefer to stay in the upper layers of the 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 oxygen. environment.

The skin of the 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.

Target: Explore external structure earthworm.

Equipment: live earthworms, Petri dishes (disposable cups), tweezers, filter paper, magnifiers, onion pieces.

Progress

The multimedia board reproduces the stages of laboratory work that students do and write down at their workplaces.

1. Examine the body of an earthworm.

Determine the size of the worm's body (length and thickness) using a ruler (bio_2007_053_p,:1.1, 1.2)

The body length of an adult earthworm is usually 15–20 cm.

Determine the segmentation of the body. Find out the same segmentation of the body throughout the body of the worm (BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.: hint)

the same segments.

Determine the shape of the body, find out how the dorsal side of the body differs from the abdominal.

Convex (dorsal) and flat (abdominal)

Determine body color. Find out how the dorsal side of the body differs from the ventral side.

Find the anterior (more pointed, closer to the girdle - thickening at the anterior end of the body) (bio_2007_053_p,:1.3; BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.1) and the posterior (more blunt) ends of the body (bio_2007_053_p,:1.4),

The anterior end of the body of the worm with a mouth opening. A small movable blade in front of the mouth is located on the ventral side of the body. In an earthworm, it has neither eyes nor tentacles.

The posterior end of the body of the worm with an anus. belt. Determine on which segments of the body the girdle is located. (bio_2007_053_p,:1.5; BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.2)

Glandular thickening of the integument. During reproduction, the cells of the girdle secrete the substance of a cocoon into which fertilized eggs are placed. Pay attention to the thinnest layer of the cuticle, which is distinguished by the skin epithelium and covers the entire body.

2. Pay attention to the skin of the worm. Determine if it is dry or wet?

3. Gently touch a piece of filter paper to the skin of the worm(bio_2007_053_p,:1.6).

The skin epithelium of earthworms is rich in mucous glands. Therefore, their skin is constantly moisturized. It has great importance in breathing, which occurs through the integument of the body when moving in the soil

4. Gently run your finger along the ventral or lateral side of the worm's body from the back to the front end(you will feel the touch of the bristles). Use a magnifying glass to examine the location of the bristles on the body of the worm (BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.3).

Each segment of the body, except for the head lobe, bears 8 setae arranged in pairs, so that 4 double rows of setae extend along the body. The earthworm moves with the help of body contractions. When moving in the soil, an important role is played by the alternating extension and expansion of the front end of the body, causing the separation of soil particles. The bristles with which the worm clings to the substrate also play a significant role in the process of locomotion.

5. What do you think is the significance of such skin and such bristles for the life of a worm in the soil?

6. Watch a worm crawl on paper(listen if he rustles bristles) (bio_2007_053_p,:2.1).

When the worm moves along rough paper, the bristles rustle against the paper. The worm clings to the substrate with bristles.

7. Watch a worm crawling on glass soaked in water. How does he move(bio_2007_053_p,:2.2)?

When moving on glass (smooth surface), the rustling of bristles is not audible: the worm does not cling to a smooth substrate with bristles. The body of the worm is strongly elongated, alternate muscle contractions are observed along the entire length of the body.

8. Touch different parts of the earthworm's body with the tip of a pencil. What are you watching?

9. Bring a piece of onion to the front end of the worm's body. What are you watching?

Irritability, defensive reflex.

10. Draw a conclusion about the features of the structure and movement of the earthworm in connection with the habitat.

Small bristle worms have an elongated segmented body. The surface of the body is constantly moistened due to the secretion of mucus by the glands of the skin epithelium. This is of great importance for breathing. The movement of oligochaetes occurs due to muscle contractions. But the bristles with which the worm clings to the substrate also play a significant role in the movement of oligochaetes. The nervous system is developed: they have irritability, protective reflexes.

Homework paragraph 13

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 of the nervous system, branching out 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.

Food

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.

It has a more complex organization than roundworms or flatworms.

In worms of the annelids species, for the first time, a secondary cavity, a highly organized blood supply system and a nervous system appear.

Earthworm: structure

In cross section, the body is almost round. The average length is about 30 cm. It is divided into 150-180 segments, or segments. The belt, located in the anterior third of the body, performs its function during sexual activity (the earthworm is a hermaphrodite). On the sides of the segments there are four stiff, well-developed small setae. They contribute to the movement of the body of the worm in the soil.

The color of the calf is reddish-brown, and on the abdomen is slightly lighter than on the back.

natural necessity

All animals have a circulatory system, starting with the secondary cavities. It was formed as a result of an increase in vital activity (compared, for example, with Life in constant motion requires stable energetic muscle work, which, in turn, causes the need for an increase in cells of incoming oxygen and nutrients, that only blood can deliver.

What is the circulatory system of an earthworm? The two main arteries are the dorsal and abdominal cavity. In each segment, looped vessels pass between the arteries. Of these, several are slightly thickened and covered with muscle tissue. In these vessels, which perform the work of the heart, the muscles, contracting, push the blood into the abdominal artery. The annular "hearts" at the exit to the spinal artery have special valves that prevent blood flow from going in the wrong direction. All vessels are divided into a large network of the thinnest capillaries. Oxygen in them comes from the air, and nutrients are absorbed from the intestines. Capillaries located in muscle tissues give off carbon dioxide and decay products.

The circulatory system of the earthworm is closed, since it does not mix with the liquid of the cavity during the entire movement. This makes it possible to significantly increase the rate of metabolism. In animals that do not have a blood pumping system, heat transfer is two times lower.

Nutrients absorbed by the intestines during the movement of the worm are distributed through a well-formed circulatory system.

Its scheme is quite complicated for this type of animal. Vessels run above and below the intestines along the entire body. The vessel passing in the back is supplied with muscles. It, contracting and stretching, pushes the blood in waves from the back to the front of the body. In the anterior segments (in certain types worms are 7-11, in others - 7-13) the vessel running along the back communicates with several pairs of vessels passing transversely to the main one (usually there are 5-7 of them). The circulatory system of the earthworm imitates hearts with these vessels. Their muscles are much more developed than the others, so they are the main ones in the entire system.

Functional features

An earthworm is similar to the hemodynamic functions of vertebrates. The blood that comes out of the hearts enters the vessel located in the abdominal cavity. It moves towards the posterior end of the body of the worm. On its way, this blood carries nutrients through smaller vessels located in the walls of the body. During puberty, blood also enters the genitals.

The structure of the circulatory system of the earthworm is such that the vessels in each organ pass into the smallest capillaries. The blood from them flows into the vessels located across the main ones, from which the blood flows into the spinal artery. Musculature is in all blood vessels, even the smallest. This allows the blood to not stagnate, especially in the peripheral part of the blood supply system of this type of annelids.

Intestines

In this part of the body of the worm there is a particularly dense plexus of capillaries. They seem to entangle the intestines. Part of the capillaries brings nutrients, the other part carries them throughout the body. The muscles of the vessels surrounding the intestines of this annular species are not as strong as those of the dorsal vessel or the heart.

Composition of the blood

The circulatory system of the earthworm is red in the light. This is due to the fact that in the blood there are substances that are similar in their chemical structure to hemoglobin, which is part of the blood composition of vertebrates. The difference lies in the fact that these substances are in the plasma (the liquid part of the blood composition) in a dissolved form, and not in the blood cells. The blood of the earthworm itself is cells without color, of several types. They are similar in structure to the colorless cells that make up the blood of vertebrates.

Transportation of oxygen cells

Oxygen cells in vertebrates transport hemoglobin from the respiratory organs. In the blood of earthworms, a substance similar in composition also brings oxygen to all the cells of the body. The only difference is that worms do not have respiratory organs. They "inhale" and "exhale" the surface of the body.

The thin protective film (cuticle) and epithelium of the skin of the worm, together with a large capillary network of the skin, guarantee a good absorption of oxygen from the air. The capillary cobweb is so large that it is even in the epithelium. From here, the blood moves through the wall vessels of the body and transverse vessels to the main stem channels, due to which the whole body is enriched with oxygen. The reddish tint of the body of this type of annelids is given precisely by a large capillary network of walls.

Here it must be taken into account that the thinnest film covering the body of the earthworm (cuticle) is very easily moistened. Therefore, oxygen is first dissolved in water droplets, which are retained by the skin epithelium. From this it follows that the skin should always be moisturized. Thus, it becomes clear that the humidity of the environment is one of the important conditions for the life of these animals.

Even the slightest drying of the skin stops breathing. For the circulatory system of the earthworm does not bring oxygen cells. It can not last very long in such conditions, using internal water supplies. The glands located in the skin help out. When the situation becomes really acute, the earthworm begins to utilize the cavity fluid, splashing it out in parts from the pores located on the back.

Digestive and nervous systems

The digestive system of earthworms consists of the foregut, midgut and hindgut. Due to the need to live more actively, earthworms have gone through several stages of improvement. The digestive apparatus has departments, each of which has a specific function.

The main organ of this system is the intestinal tube. It is divided into the oral cavity, pharynx, esophagus, stomach (muscular body), middle and hind intestines, anus.

The ducts of the glands go into the esophagus and pharynx, which affect the pushing of food. In the midgut, food is chemically processed and the products of digestion are absorbed into the blood. The rest comes out through the anus.

Along the entire length of the body of the worm, from the side of the peritoneum, there is a nerve chain. Thus, each segment has its own developed nerve lumps. In front of the neural chain is an annular jumper, consisting of two connected nodes. It is called the peripharyngeal nerve ring. A network of nerve endings radiates from it throughout the body.

The digestive, circulatory and nervous systems of the earthworm are much more complicated, due to the progress of the entire type of annulus. Therefore, in comparison with other types of worms, they have a very high organization.