The value of wet earthworm skin. 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 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.

Target: Explore external structure earthworm.

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

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

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.

Which circulatory system 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 environment- one of 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.

BODY COVERS - earthworms.

body of earthworms covered with a single layer of epithelium. It contains supporting, glandular, and cambial cells (Fig. 5).

Rice. 5. Skin epithelium of the earthworm. (According to Stephenson).

1 - protein gland; 2 - cuticle; 3 - supporting cells; 4 - mucous cells; b - cambial cells.

Supporting cells carry out a protective function. The outer part of these cells secretes the substance of the cuticle - a thin transparent film,
winged epithelium. The cuticle consists of two systems of parallel fibers intersecting each other at right angles. There may be holes in the cuticle at the intersections. The direction of the fibers is diagonal with respect to the longitudinal axis of the body (Fig. 6), which the best way ensures the strength of the cuticle when stretched from the inside (it is curious that the connective tissue fibers in the skin of mammals also have a diagonal arrangement with respect to the longitudinal axis of the body). The cuticle wears out all the time during life and is renewed by the activity of the epithelium. In canned specimens, the cuticle may lag behind, and sometimes it can be removed entirely, like a stocking.

The cuticle is responsible for the smoothness of the skin surface, which makes it easier for the body to glide over hard surfaces. It also determines the characteristic glossiness of the surface of the body.

Of great importance in the life of worms is activity of glandular cells. Most of them secrete a mucous substance, which is always smeared on the surface of the cuticle; it comes to the surface of the body through holes in it (Fig. 5 and 6). This increases the ease of gliding over the substrate and prevents the body from drying out. With any strong irritation, mucous secretions come to the surface of the body in huge quantities: the worm is instantly wrapped in a thick layer of thick sticky mucus. The formation of a mucous sheath on the body plays an important role in mating and the formation of egg cocoons. In addition, mucous secretions coat the walls of the worms' passages inside the soil, which gives them considerable strength *

Rice. 6. Cuticle of an earthworm from the surface. (From Stolte).

1 - cuticle fibers; 2 - openings of the glands.

In addition to the usual mucous cells, in the skin epithelium of earthworms there are on the entire surface of the body
the so-called protein glandular cells (Fig. 5). In the region of the girdle (Fig. 25), near the setae of the genital openings and in other places of the body, there are skin glands, the significance of which will be discussed later.

An important component of the skin epithelium are small cells located in its deep part, on the border with the subject and muscles, and not in contact with the outer parts of the supporting and glandular cells (fps. 5). These are the cambial cells, which are the reserve; due to them, worn-out functioning cells are renewed and tissue growth occurs in young animals. These cells are also mobilized during wound healing after wounds and other injuries.

Fig. 7. The bristle sac of an earthworm in longitudinal section. (From Stolte).

1 - he led; 2.3 - muscles; 4 - bristle mark wall

Bristles are also formed from special cells of the skin epithelium. Only the outer part of the setae protrudes from the surface of the body. With its inner end, it is deeply immersed in the body wall and can penetrate it through, almost reaching the body cavity. The bristles are placed in bristle sacs, which are ingrowths into the body of the skin epithelium (Fig. 7). They consist of a substance similar to the substance of the cuticle, are fragile and wear out quickly. Therefore, throughout life, new setae are formed in the depths of the bristle pouches. Each bristle is formed from one cell, which is part of the bottom of the pouch.

The bristles of earthworms are unequal in shape: they are rods, sometimes almost completely straight, sometimes with distinctly curved toes.

At some distance from the outer end of the seta there is a small thickening - a nodule, i.e., a place to which the muscles are attached that draw the seta into the depths of the body (retractor muscles; Fig. 7). In addition to them, in the bristle sacs there are protractor muscles, which are attached at one end to the end of the bristle, and at the other - to the body wall; by their contraction, the bristle is pushed outward, and also (if they are not simultaneously contracted) it can perform quite a variety of movements.

Speaking of integuments of the body, let us mention the interesting phenomenon of the glow of earthworms, which has long attracted the attention of many major naturalists. In particular, the well-known researcher of insect life, Fabre, wrote about luminous earthworms. AT different countries special types of "phosphoric" worms are described. It turned out however; that glow in the dark can be observed in the most common species. The well-known Czech explorer Vejdovsky reported that, while digging up a dunghill one night in search of earthworms, he saw patches of flickering bluish-white light that appeared and disappeared in different points. It turned out that the light came from ordinary striped dung worms, which he collected in large numbers. He noticed that his fingers, after he took the worms, began to glow in the dark. Thus, the mucous secretions of worms glow, and only under special conditions, since glow is not always observed. There are indications of the glow of the liquid protruding from the oral and anal openings.

There can be no doubt that in all these cases the glow is caused by bacteria contained in the secretions of the worms. In the process of vital activity of many bacteria, light energy is released, which is released during chemical reactions. It must be said that almost always the glow of animals owes its origin to bacteria, one way or another connected with it.

Some researchers believe that the glow is useful for worms: some think that flashes of light help individuals find each other on the surface of the earth when mating (although worms do not have eyes, they are still able to perceive light on the surface of the front of the body); others attribute the glow to the role of a factor that repels enemies; still others think that the glowing slime left by the worms in their path attracts the attention of enemies and makes them less visible. However, all this is nothing more than speculation, not supported by accurate observations.

Annelids have the highest organization compared to other types of worms; for the first time they have a secondary body cavity, a circulatory system, a more highly organized nervous system. In annelids, another, secondary cavity was formed inside the primary cavity with its own elastic walls from mesoderm cells. It can be compared to airbags, a pair in each segment of the body. They "swollen", filled the space between the organs and support them. Now each segment has received its own support from the bags of the secondary cavity filled with liquid, and the primary cavity has lost this function.

They live in soil, fresh and sea water.

External structure

The earthworm has an almost round body in cross section, up to 30 cm long; have 100-180 segments, or segments. In the anterior third of the body there is a thickening - a girdle (its cells function during the period of sexual reproduction and oviposition). On the sides of each segment, two pairs of short elastic bristles are developed, which help the animal when moving in the soil. The body is reddish-brown in color, lighter on the flat ventral side and darker on the convex dorsal side.

Internal structure

characteristic feature internal structure is that earthworms have developed true tissues. Outside, the body is covered with a layer of ectoderm, the cells of which form the integumentary tissue. The skin epithelium is rich in mucous glandular cells.

muscles

Under the cells of the skin epithelium there is a well-developed musculature, consisting of a layer of annular and a more powerful layer of longitudinal muscles located under it. Powerful longitudinal and annular muscles change the shape of each segment separately.

The earthworm alternately compresses and lengthens them, then expands and shortens them. Wave-like contractions of the body allow not only to crawl along the mink, but also to push the soil apart, expanding the course.

Digestive system

The digestive system begins at the front end of the body with a mouth opening, from which food enters sequentially into the pharynx, esophagus (in earthworms, three pairs of calcareous glands flow into it, the lime coming from them into the esophagus serves to neutralize the acids of rotting leaves that animals feed on). Then the food passes into an enlarged goiter and a small muscular stomach (the muscles in its walls contribute to the grinding of food).

From the stomach almost to the rear end of the body stretches the middle intestine, in which, under the action of enzymes, food is digested and absorbed. Undigested residues enter the short hindgut and are thrown out through the anus. Earthworms feed on half-decayed plant remains, which they swallow along with the earth. When passing through the intestines, the soil mixes well with organic matter. Earthworm excrement contains five times more nitrogen, seven times more phosphorus and eleven times more potassium than ordinary soil.

Circulatory system

The circulatory system is closed and consists of blood vessels. The dorsal vessel stretches along the entire body above the intestines, and under it the abdominal vessel.

In each segment, they are united by an annular vessel. In the anterior segments, some annular vessels are thickened, their walls contract and pulsate rhythmically, due to which blood is distilled from the dorsal vessel to the abdominal one.

The red color of blood is due to the presence of hemoglobin in the plasma. It plays the same role as in humans - the nutrients dissolved in the blood are carried throughout the body.

Breath

Most annelids, including earthworms, are characterized by skin respiration, almost all gas exchange is provided by the surface of the body, so the worms are very sensitive to wet soil and are not found in dry sandy soils, where their skin dries out quickly, and after rains, when in the soil a lot of water, crawl to the surface.

Nervous system

In the anterior segment of the worm there is a peripharyngeal ring - the largest accumulation of nerve cells. From it begins the abdominal nerve chain with nodes of nerve cells in each segment.

Such a nervous system of a knotty type was formed by the fusion of the nerve cords of the right and left sides of the body. It ensures the independence of the segments and the coordinated work of all organs.

excretory organs

The excretory organs look like thin loop-shaped curved tubes, which open at one end into the body cavity, and at the other outward. New, simpler funnel-shaped excretory organs - metanephridia - remove harmful substances into the external environment as they accumulate.

Reproduction and development

Reproduction occurs only sexually. Earthworms are hermaphrodites. Their reproductive system is located in several segments of the anterior part. The testicles lie in front of the ovaries. When mating, the spermatozoa of each of the two worms are transferred to the spermatozoa (special cavities) of the other. Worms are cross fertilized.

During copulation (mating) and oviposition, the cells of the girdle on the 32-37th segment secrete mucus, which serves to form an egg cocoon, and a protein liquid to feed the developing embryo. The secretions of the girdle form a kind of mucous sleeve (1).

The worm crawls out of it with its rear end forward, laying eggs in the mucus. The edges of the muff stick together and a cocoon is formed, which remains in the earthen burrow (2). Embryonic development of eggs occurs in a cocoon, young worms emerge from it (3).

sense organs

The sense organs are very poorly developed. The earthworm does not have real organs of vision, their role is performed by individual light-sensitive cells located in the skin. The receptors for touch, taste, and smell are also located there. Earthworms are capable of regeneration (easily restores the back).

germ layers

The germ layers are the basis of all organs. In annelids, the ectoderm (outer layer of cells), endoderm (inner layer of cells) and mesoderm (intermediate layer of cells) appear at the beginning of development as three germ layers. They give rise to all major organ systems, including the secondary cavity and the circulatory system.

These same organ systems are preserved in the future in all higher animals, and they are formed from the same three germ layers. Thus the higher animals in their development repeat the evolutionary development of their ancestors.