How do earthworms move? The role of the earthworm in nature. Breath of an earthworm. Respiratory system of insects - locusts Does an earthworm breathe oxygen?

Type Annelids

General characteristics of the type Annelids (ringed worms)

General characteristics of the type

Annelids (ringworms) are a large type (about 9 thousand species) of higher free-living marine, freshwater and soil animals that have a more complex organization than flatworms and roundworms. This primarily applies To marine polychaete worms, which are a key group in the evolution of higher invertebrates: mollusks and arthropods evolved from their ancient ancestors.

The main progressive features of the ring structure are as follows:

1. The body consists of numerous (5-800) segments(rings). Segmentation is expressed not only in external, but also in internal organization, in the repetition of many internal organs, which increases the survival of the animal in case of partial damage to the body.

2. Groups of segments similar in structure and function in polychaete worms are combined into body parts- head, trunk and anal lobes. The head section was formed by the fusion of several anterior segments. Body segmentation in oligochaete worms homogeneous.

3. Body cavity secondary, or in general, lined with coelomic epithelium. In each segment, the coelom is represented by two isolated sacs filled with coelomic fluid.

Figure 11.7. Head end of the Nereid: I1-eyes; 2 - tentacles; 3 -antennae; 4 - parapodia with tufts of setae.

4. The skin-muscle bag consists of a thin elastic cuticles, located underneath single layer epithelium and two muscle layers: outer - roundabout, and internal - highly developed longitudinal

5. For the first time, specialized organs of movement appeared - parapodia - They are lateral bilobed outgrowths of the body walls of the trunk segments into which the coelom extends. Both lobes (dorsal and ventral) bear more or less number of setae (Fig. 11.7). In oligochaete worms there are no parapodia, there are only tufts with a few setae.

6. In the digestive system, which has three sections, the foregut is highly differentiated into a number of organs (mouth, pharynx, esophagus, crop, stomach).

7. First developed circulatory system closed. It consists of large longitudinal dorsal And abdominal vessels, connected in each segment ring vessels(Fig. 11.8). The movement of blood is carried out due to the pumping activity of the contractile areas of the spinal cord, and less commonly of the annular vessels. Blood plasma contains respiratory pigments similar to hemoglobin, thanks to which ringworms have populated habitats with very different oxygen content.

8. Respiratory organs polychaete worms -gills; these are thin-walled, leaf-shaped, feathery or bushy outer outgrowths of part of the dorsal lobes of the parapodia, penetrated by blood vessels. Oligochaete worms breathe over the entire surface of their body.

9. Excretory organs - located in pairs in each segment metanephridia, removing end products of vital activity from the cavity fluid. The funnel of metanephridia is located in the coelom of one segment, and the short tubule coming from it opens outward in the next segment (see Fig. 11.8,6).

10. Nervous system ganglion type. It consists of pairs supraglottic And subpharyngeal ganglia, connected nerve trunks in the peripharyngeal nerve ring, and many pairs of ganglia ventral nerve cord, one pair in each segment (Fig. 11.8, a). The sense organs are varied: vision (in polychaete worms), touch, chemical sense, balance.

11. Overwhelming majority kolchetsov- dioecious animals, less often hermaphrodites. The gonads develop either under the coelomic epithelium in all body segments (in polychaete worms), or only in some (in oligochaete worms). In polychaete worms, germ cells enter the coelomal fluid through breaks in the coelomic epithelium, from where they are released into the water by special sex funnels or metanephridia. In most aquatic ringlets, fertilization is external, while in soil forms it is internal. Development with metamorphosis(in polychaete worms) or direct (in polychaete worms, leeches). Some types of ringworms, in addition to sexual reproduction, also reproduce asexually (by fragmentation of the body with subsequent regeneration of the missing parts). The phylum Annelids are divided into three classes - Polychaetes, Oligochaetes and Leeches.

Type Annelids. general characteristics

The main characteristic features of annelids are:

-secondary, or coelomic, cavity bodies;

Appearance circulatory And respiratory systems;

Excretory system in the form metanephridia.

a brief description of

Class oligochaetes

Class Oligochaete worms unites 4-5 thousand species. Their body length ranges from 0.5 mm to 3 m.

Audio fragment "Class Oligochaete worms"(00:54)

Internal structure earthworm

Body coverings and muscles. The skin of a worm consists of a single layer of integumentary cells. Among them there are cells that secrete mucus. Under the skin there are circular and longitudinal muscles. When the ring muscles contract, the earthworm's body lengthens, becomes thinner, and moves forward. When the longitudinal muscles contract, the back part is pulled towards the front. Movement occurs in waves.

Virtual laboratory work

Body cavity. As we already know, the earthworm is a three-layered animal. Its body consists essentially of two tubes nested inside one another. The outer tube represents the wall of the body, and the inner tube represents the wall of the digestive tract. body cavity, lined inside with a layer of cells , is located between them. In the cavity fluid (it gives the body elasticity) there are internal organs.

Digestive system. The digestive tract begins with the mouth, followed by the pharynx, esophagus, crop, stomach, intestines and anus.

Circulatory system. The circulatory system is designed to move oxygen, carbon dioxide, nutrients and other substances within the body. In an earthworm, blood does not flow freely into the body cavity, but moves only inside the vessels. This circulatory system is called closed . The circulatory system consists of two main vessels : dorsal and abdominal. Blood flows forward through the spinal cord, and backward through the abdominal tract. In the region of the esophagus, these vessels are connected by ring vessels called “hearts”. They have muscular walls with which they pump blood into the abdominal vessel. Small blood vessels extend to all organs and to the walls of the body.

Respiratory system.

Respiratory system. The earthworm has no respiratory organs. Breathing occurs through moist skin riddled with blood vessels.

Excretory system. The excretory system is represented by paired organs (excretory tubes) located in each segment of the body. With the help of the excretory system, the body removes excess water and other substances.

Nervous system. The nervous system consists of a peripharyngeal nerve ring and a ventral nerve cord with thickenings in each segment from which nerves arise. The peripharyngeal ring consists of the suprapharyngeal and subpharyngeal nerve nodes, connected by an annular bridge. There are no special sense organs, but sensitive cells in the skin allow the earthworm to sense touch and distinguish light from dark. The excitation that arises in these cells is transmitted along nerve fibers to the nearest nerve node, and from there to others. nerve fibers– to the muscles, which causes their contraction. Thus nervous system carries out the body's response to irritation (reflex).

2. Reproduction and development

The earthworm is capable of reproducing both asexually and sexually. During asexual reproduction, the earthworm's body splits into two parts, and then, through regeneration, each of them “completes” the missing parts of the body.

3. The importance of earthworms

Annelids serve as important links in the food chains of natural biogeocenoses. For example, moles, hedgehogs, frogs, toads, and birds feed on earthworms. Other worms (for example, tubifex) – fish (carp, crucian carp).

Earthworms bring great benefits to humans by loosening the soil. They make it more porous, more accessible for the penetration of air and water, which facilitates plant growth and increases the yield of agricultural crops. While burrowing in the ground, worms swallow pieces of soil, crush them and throw them away along with organic matter.

Charles Darwin became interested in earthworms as a young man. In 1837, he made a report at the Geological Society of London on the topic: “On the formation of the soil layer,” in which he outlined the theory according to which soil particles are constantly carried by earthworms from the depths to the surface, due to which objects lying on the ground end up on after a few years at a depth of 6–10 cm under the turf. Thus, the entire soil layer ends up passing through the stomach of the earthworms.

Charles Darwin was struck by the following observations: worms pull leaves into a hole by grabbing them by the top (not by the petiole), so the leaf offers the least resistance when dragged into the hole (after all, the top of the leaf is narrower than its base). But pine needles are always pulled by the worms by the petiole, that is, the base common to double needles. And in this case the object offers the least resistance. In his experiments, Darwin placed triangles cut out of paper on the worms, and they pulled them in in the most appropriate way: by one of the sharp corners. Further research showed that reflexes play a leading role in this process.

Earthworms are capable of learning. They were placed in a T-maze: the longest corridor that formed the base of the letter T. When the worms crawled to the end, they were given the choice of turning right or left. On the right, darkness and food awaited them; on the left, a weak electric shock awaited them. After a series of such “lessons,” the worms developed a reflex to unerringly move in the right direction, toward food.

Type Annelids. Class Oligochaetes

GENERAL CHARACTERISTICS

Structure and covers . Body of oligochaete worms (oligochaete) highly elongated, cylindrical, consists of lying one after another rings, or segments. All segments have a similar structure, i.e. for the organization of oligochaetes (and all annelids) is typical repeatability of structure, or metamerism. Each segment, except the very first, is equipped small bristles, usually arranged in four bundles - a pair of side And a pair of abdominal. The anterior segment is head blade - prostomium devoid of eyes and antennae. He carries mouth opening. Last segment - anal paddle, or pygidium, - carries powder.

The integuments of oligochaetes are represented epithelium, forming a thin surface elastic cuticle (Fig. 1). The epithelium is rich glandular cells.

Skin-muscle bag . Under the epithelium there are well-developed muscle layers. Outer layer presented circular muscle fibers. Due to the contraction of this layer, the body of the worm becomes thinner and elongated. Inner layer, more powerful, introduced longitudinal muscle fibers, due to the contraction of which the body of the worm thickens and shortens.

Rice. 1.Cross section of the middle part of the body of an earthworm: 1 - cuticle; 2 - epidermis; 3 - layer of circular muscles; 4 - layer of longitudinal muscles; 5 - coelomic epithelium; 6 - metanephridium; 7 - bristles; 8 - mesentery; 9 - abdominal vessel; 10 - subneural vessel; 11 - abdominal nerve chain; 12 - chloragogenic cells; 13 - intestinal cavity; 14 - vascular plexus; 15 - typhlosol; 16 - typhlosol vessel; 17 - dorsal vessel

Between the intestines and the skin-muscular sac is located secondary body cavity , or in general -space bounded by its own epithelial walls of mesodermal origin and containing coelomic fluid (Fig. 2). The structure of the coelom differs from the primary body cavity in the presence coelomic lining - own wall. The lining is formed two sheets of paper. One is adjacent to the body wall, the other is adjacent to the intestinal walls. Above and below the intestine, both leaves grow together, forming mesentery(mesentery), which divides the whole to the left And right side. In addition, there are transverse partitions which divide the body cavity into cameras, corresponding to the boundaries of the rings. The whole is filled with liquid in which phagocytes, eggs, and sperm float. Coelomic fluid, washing the internal organs, supplies them with oxygen and nutrients, and also promotes the removal of metabolic products and the movement of phagocytes. Just like the fluid that fills the primary body cavity in roundworms, coelomic fluid may play a role hydroskeleton.

Digestive system oligochaete well differentiated (Fig. 3). It begins mouth opening. The intestines consist from three departments - front, average And rear. The most differentiated part of the intestine is the anterior part of the intestine, consisting of the pharynx, esophagus and muscular stomach. Sometimes there is a goiter in front of the stomach. In the midgut, to increase the absorption surface, an invagination is formed into the intestinal lumen - typhlosol.

Rice. 2.Development of the coelom in annelids. A-B - cross sections of three successive stages of segment development: 1 - intestine; 2 - primary body cavity; 3 - whole; 4 - outer wall of the coelomic sac; 5 - dorsal mesentery; 6 - inner wall of the coelomic sac; 7 - abdominal mesentery; 8 - abdominal nerve trunks

Circulatory system closed and consists of two main longitudinal vessels - dorsal and abdominal. The dorsal vessel runs along the entire body above the intestine, the abdominal vessel - below it. The cavity of the blood vessels is a remnant of the primary body cavity. Both vessels are connected by ring vessels located metamerically. The movement of blood through the vessels is ensured by the pulsation of the dorsal vessel and some annular vessels of the anterior part of the body, therefore called the lateral, or annular, hearts. In the dorsal vessel, blood flows forward, in the abdominal vessel - backward. Through the annular vessels, blood moves from the dorsal vessel to the abdominal vessel in the anterior part of the body and in the opposite direction - in the posterior segments. The blood may be red in color from iron, similar to vertebrate hemoglobin, dissolved in the blood fluid.

Rice. 3.The structure of an earthworm (dissected worm): 1 - pharynx; 2 - esophagus; 3 - calcareous glands; 4 - goiter; 5 - stomach; 6 - midgut; 7 - dorsal fold of the intestine (in section); 8 - suprapharyngeal nerve ganglion; 9 - node of the abdominal nerve chain; 10 - dorsal blood vessel; 11 - annular vessels covering the pharynx; 12 - abdominal nerve chain; 13 - metanephridia; 14 - testes; 15 - seed ducts; 16 - seed sacs; 17 - ovaries; 18 - oviducts; 19 - seminal receptacles; 20 - partitions of the body cavity

Excretory system presented metanephridia. Metanephridia begins in the body cavity as a funnel - nephrostomy. From the funnel there is a duct that passes through the septum, enters the adjacent segment and opens outward excretory time in the lateral wall of the body. Each segment contains a pair of metanephridia - right and left. The funnel and duct are equipped with cilia, causing the movement of the secreted fluid.

Nervous system. central part nervous system consists of paired cerebral ganglia - suprapharyngeal and subpharyngeal, connected by two peripharyngeal connectives (nerve trunks connecting opposite ganglia). This way it is formed peripharyngeal ring. The central part of the nervous system includes paired ventral nerve trunk. In each segment the trunks have thickenings - ganglia, which are connected to each other by jumpers - commissures (transverse nerve trunks connecting the ganglia of one segment). Formed ventral nerve cord, similar to a staircase. Each ganglion innervates all organs of the segment in which it is located.

Sense organs Oligochaetes have very poorly developed due to their burrowing lifestyle. Eyes almost always are missing. However, there are light sensitive cells scattered in large numbers in the skin, which allows oligochaetes to have sensitivity to light.

Reproductive system. Oligochaetes - hermaphrodites, But fertilization they have - cross internal. The reproductive gonads are localized in the genital segments. Male gonads - testes - lie in seed capsules, which are located in the seed sacs. Women's reproductive system presented a pair of ovaries, a pair of oviducts And egg sacs.

Reproduction and development. Development is direct without a larval stage. The eggs develop inside an egg cocoon, which is formed in the girdle area.

In addition to sexual reproduction, oligochaetes exhibit asexual reproduction, similar to asexual reproduction eyelash worms. The body of the worm is divided into two halves: the rear part of the body regenerates in the front, and the head part of the body in the back.

Annelids have the most high organization compared to other types of worms; For the first time, they have a secondary body cavity, a circulatory system, and a more highly organized nervous system. In annelids, inside the primary cavity, another, secondary cavity has formed with its own elastic walls made of mesoderm cells. It can be compared to airbags, one pair in each segment of the body. They “swell”, fill the space between the organs and support them. Now each segment received its own support from the bags of the secondary cavity filled with liquid, and the primary cavity 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 - the girdle (its cells function during the period of sexual reproduction and egg laying). On the sides of each segment there are two pairs of short elastic setae, 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

A characteristic feature of the internal structure is that earthworms have developed real tissues. The outside of 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 muscle, consisting of a layer of circular muscles and a more powerful layer of longitudinal muscles located under it. Powerful longitudinal and circular 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 crawling through the burrow, but also pushing the soil apart, expanding the movement.

Digestive system

The digestive system begins at the front end of the body with the mouth opening, from which food enters sequentially into the pharynx and 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 on which the animals feed). Then the food passes into the enlarged crop and a small muscular stomach (the muscles in its walls help grind the food).

The midgut stretches from the stomach almost to the posterior end of the body, in which, under the action of enzymes, food is digested and absorbed. Undigested remains enter the short hindgut and are thrown out through the anus. Earthworms feed on half-rotted plant remains, which they swallow along with the soil. As it passes 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 regular 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 below it is the abdominal vessel.

In each segment they are united by a ring vessel. In the anterior segments, some annular vessels are thickened, their walls contract and pulsate rhythmically, thanks to which blood is driven 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 - nutrients dissolved in the blood are distributed throughout the body.

Breath

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

Nervous system

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

This nodular type nervous system was formed by the fusion of nerve cords on the right and left sides of the body. It ensures the independence of the joints and the coordinated functioning 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 outside. New, simpler funnel-shaped excretory organs - metanephridia excrete 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 testes lie in front of the ovaries. When mating, the sperm of each of the two worms is transferred to the seminal receptacles (special cavities) of the other. Cross fertilization of worms.

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

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

Sense organs

The sense organs are very poorly developed. The earthworm does not have real organs of vision; their role is played 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 restore the back part).

Germ layers

The germ layers are the basis of all organs. In annelids, the ectoderm ( outer layer cells), endoderm (inner layer of cells) and mesoderm (intermediate layer of cells) appear early in 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 subsequently preserved in all higher animals, and they are formed from the same three germ layers. This is how higher animals repeat in their development evolutionary development ancestors

And the cylindrical shape provides an optimal ratio of volume and surface area involved in oxygen production. Considering that they move quite little, we can say that such breathing through the skin is quite enough for them.

However, worms have a circulatory system, unlike single-celled organisms and some types of insects, rain hemoglobin is dissolved, which is distributed throughout the body through contraction of large vessels during the movement of the worm. This distributes oxygen throughout the body, helping to maintain diffusion. Large vessels are one vein and one artery, which is exactly how many vessels the worm has (except for the capillaries located under the cuticle).

In principle, the earthworm does not have skin as such, like mammals, but has a very thin covering - the cuticle. Such skin is moistened by epithelial secretions, and due to its minimal thickness allows the worm to breathe. However, such skin is not protected from drying out, so the worms must live in some kind of moist environment in order to protect the skin from drying out. Oxygen is first dissolved in the water that covers the body of the worm, and only then is absorbed into the blood through the capillaries. If the worm's skin dries out, it cannot receive environment oxygen dies.

Since rainwater practically does not come to the surface, such a breathing system turns out to be extremely beneficial for it - it can take oxygen directly from the soil for gas exchange. There is enough oxygen between the earth particles to supply the worm. When it rains, worms crawl out of the ground to the surface, this is due to the fact that water glues the particles of the earth together, and there is no air between them. To get the oxygen they need, the worms must rise to the surface.

To test the breath of an earthworm, you can conduct a simple experiment: pour earth into a jar and place several on top. After a short time, the worms will burrow into the ground, but if you water the ground, they will rise to the surface. In a similar way, all annelids use the skin, covering the entire surface of the body.

An earthworm is a representative of the annelid phylum. Its long, elongated body consists of separate segments - rings, separated by annular constrictions, which explains the name of the species. Thanks to this structure, it can move freely both in dense soil and on the soil surface.

Instructions

The body of the earthworm is elongated by 10-16 cm in length. It is round in cross section, but is longitudinally divided by annular constrictions into 100-180 segments. They contain elastic bristles with which the worm clings to uneven soil while moving.

During the day, worms are in the soil and make tunnels in it. They easily drill through the soft one with the front end of the body: first it becomes thin, and the worm pushes it forward between lumps of earth, then, thickening, the front end pushes the soil apart, and the worm pulls up the back part of the body. In dense soil, worms can eat their way through the digestive tract. At night they come to the surface of the soil and leave behind characteristic earthen piles.

The skin of an earthworm is moist to the touch because it is covered, which facilitates the movement of the worm in the soil. Oxygen needed for breathing can also only penetrate through moist skin. Below it is skin-muscle sac– circular (transverse) muscles fused with the skin, under which lies a layer of longitudinal muscles. The former make the animal's body long and thin, the latter - thickened or shortened. The coordinated alternating work of these muscles ensures the movement of the worm.

Under the skin-muscle sac you can see a body cavity filled with fluid. It contains the internal organs of the animal. Unlike roundworms, the body cavity of earthworms is not solid, but segmented, divided by transverse walls.

Earthworm belongs to the group of annelids. It does not have any special organs specifically designed for gas exchange, and gas exchange occurs by diffusion across the entire surface of the body. In essence, they do not need specialized organs, since, due to the cylindrical shape of the body, their surface area to volume ratio is large, and with their relatively low activity, they do not consume much oxygen.

However, in annelids there is a circulatory system (unlike some simpler animals and single-celled organisms), and the respiratory pigment hemoglobin is dissolved in their blood. Contractions of large blood vessels drive blood along with gases dissolved in it throughout the body; this also contributes to the maintenance of steep diffusion gradients.

Thin skin of an earthworm(cuticle) is constantly moistened by the secretion of the glands located in the epithelium. Capillaries are located in the epithelium directly under the cuticle. The distance between the blood vessels and the surface of the body is small and this ensures rapid diffusion of oxygen into the blood. Earthworms are practically not protected from drying out and therefore try to stay only in a humid environment.

Respiratory system of insects - locusts.

Gas exchange in insects carried out through a system of tubes, the so-called trachea. This system allows oxygen to flow from the air directly to the tissues and there is no need for its transportation by blood. It's much more quick way, rather than the diffusion of dissolved oxygen through tissue; Such gas exchange creates conditions for high metabolic rate.

Spiracles- paired openings located on the second and third thoracic and on the first eight abdominal segments of the insect’s body lead to air cavities. Branched tubes - tracheas - extend from these cavities. Each trachea is lined by an epithelium that secretes a thin layer of chitinous material. Typically, this tough layer is further reinforced by spiral and annular thickenings, due to which the airways remain open even if the pressure in the lumen of the trachea is negative (compare with the cartilaginous rings in the human trachea and bronchi). In each body segment, the trachea branches into numerous smaller tubes called tracheoles; tracheoles also branch, penetrating the tissues of the insect, and in the most active tissues, for example in the flight muscles, they end blindly inside individual cells. The degree of branching of tracheoles can vary depending on the metabolic needs of the tissues.

Tracheoles have chitinous lining absent. At rest they are filled with watery fluid; at this time, oxygen diffuses through them to the tissues (and CO 2 in the opposite direction) at a speed quite sufficient to satisfy the needs of the insect. In the active state, increased metabolic activity of the muscles leads to the accumulation of certain metabolites, in particular lactic acid, and the osmotic pressure in the tissues increases accordingly. When this happens, the fluid from the tracheoles, under the influence of osmotic forces, is partially absorbed into the tissues, and more air enters the tracheoles, and therefore more oxygen, and this oxygen is supplied directly to the tissues just when they need it.

The overall air flow passing through the insect's body is regulated by a mechanism closing the spiracles. The opening of each spiracle is equipped with a system of valves controlled by very small muscles. The edges of this opening are covered with hairs, which prevent foreign particles from entering the spiracles and prevent excessive loss of moisture. The size of the hole is adjusted depending on the amount of CO 2 in the insect’s body.

Increased activity leads to increased formation of CO 2. Chemoreceptors they catch this and the spiracles open. The same stimulus can also cause ventilatory movements of the body, especially in large insects such as locusts. The dorsoventral muscles, contracting, make the insect's body flatter, as a result of which the volume of the tracheal system decreases and air is pushed out of it (“exhalation”). Air absorption (“inhalation”) occurs passively when the body segments, due to their elasticity, return to their original shape.

Judging by some data, thoracic and abdominal spiracles open and close alternately, and this, combined with the ventilation movements of the body, creates a unidirectional flow of air that enters the insect's body through the thoracic region and exits through the abdominal region.

Tracheal system, of course, is very effective in terms of gas exchange, however, it should be borne in mind that gas exchange in most insects is determined exclusively by the diffusion of oxygen through the tissues of the insect. Diffusion, as is known, is effective only over short distances, and this imposes severe restrictions on the size that insects can reach. These small distances at which diffusion is quite effective do not exceed 1 cm; therefore, although there are insects up to 30 cm long, their body should not be more than 2 cm thick.

Earthworm – Lumbricus terrestris(type Annelids, class Oligochaetes, family Lumbricidae) lives in moist, humus-rich soil. It feeds on organic matter, passing soil and plant debris through its intestines. Even Charles Darwin noted the beneficial effect of earthworms on soil fertility. By dragging the remains of plants into the burrows, they enrich it with humus. By making passages in the soil, they facilitate the penetration of air and water to the roots of plants.

Active earthworms in the warm season. In winter they hibernate. Freezing kills the worms instantly, so they must burrow deeper into the ground, where low temperatures do not penetrate. In the spring, when the temperature reaches a suitable level and the ground is saturated with rainwater, their mating season begins. They reproduce very quickly, producing about a hundred young worms per year. In summer, worms are not as active. There is very little food - dying plant debris - at this time, and the soil is deprived of moisture, which can cause the death of worms. Autumn period again characterized by worm activity. At this time, reproduction of offspring begins again, which lasts until the onset of winter.

Earthworms live relatively long. Some manage to live for about ten years if they do not become victims of birds and moles. Another threat to their life is the pesticides that are so widely used in gardening today.

So, the earthworm has an elongated, cylindrical body from 10 to 30 cm long. Dorsal side more rounded, it is darker, the dorsal blood vessel is visible through its skin. Abdominal side somewhat flattened and lighter colored. The anterior end of the body is thicker and darker in color. The body consists of rings - segments. In an adult worm, their number reaches 200. In the area of ​​32-37 body segments there is belt, rich in mucous glands. External segmentation corresponds to the division of the body cavity by partitions into separate chambers and segmental (i.e. in each segment) row arrangement internal organs. On each segment 8 bristles(they are easy to detect if you run your finger along the body of the worm in the direction from the rear end of the body to the front). The setae are arranged in four pairs on the lateral sides of the segments. Clinging to uneven soil, the worm moves forward with the help of the muscles of the skin-muscular sac.

Veils. The earthworm's body is covered skin-muscle bag. He is educated cuticle, single layer epithelium and two layers of muscles - external circular and internal longitudinal. The skin epithelium of the worm is rich mucous glands, which produce slime, covering the entire body of the worm and protecting it from drying out. Mucus also makes crawling in burrows easier by reducing friction with the soil.

Movement of an earthworm. When a worm crawls, waves of muscle contractions run through its body, and both the length and thickness of individual parts of its body are constantly changing. The movements produced by each part of the body consist in the fact that its constituent segments either stretch and become thinner, or contract and become thicker. As a result of such alternating stretching and contraction, the worm gradually moves forward: first, its head end is pulled forward, and then the posterior segments of the body are gradually pulled towards it; after this, the rear end of the body remains in place, and the head end is pushed even further forward, and thus the further advancement of the worm continues (it is convenient to observe it by letting the worm crawl along paper spread on the table).

Body cavity. Inside the skin-muscle sac of annelids there is secondary body cavity, or in general. This body cavity is not limited by muscles, like in roundworms, but has its own epithelial(coelomic) lining, i.e. inner side The longitudinal muscles are lined with epithelium of mesodermal origin, and there is also an epithelial lining on the side of the intestine lying in the body cavity. Due to the coelomic epithelium, internal two-layer transverse partitions are formed between the segments - dissepiments. The secondary cavity is divided into chambers, each segment containing a pair of coelomic sacs. The coelomic fluid is under pressure and plays a role hydroskeleton, so the worm feels elastic to the touch.

Digestive system comprises front, average And hindgut. Mouth located on the second segment on the ventral side of the body. Anal hole

type Annelids Earthworm

At the posterior end of the body, it looks like a small slit. Due to feeding on rotting plant remains and humus, the digestive system has a number of features. Its anterior section is differentiated into muscular throat, esophagus, goiter and muscular stomach. To increase the absorption surface, a fold has formed on the upper part of the intestine typhlosol(typhlozolis). Please note: differentiated sections of the foregut - pharynx, esophagus, crop, stomach - were absent in previous types of worms.

Breath. An earthworm breathes over the entire surface of its body due to the presence of a dense subcutaneous network of capillary blood vessels. Therefore, it is important that the worm’s body covers do not dry out, but excessive moisture (for example, very wet soil after rain) is just as destructive for them.

Circulatory system closed, that is, blood moves through the vessels without spilling into the body cavity. The movement of blood is determined by the pulsation of large vessels, mainly surrounding the esophagus. These are kind of hearts. Blood supplies all organs and tissues with nutrients, transporting them from the intestines, and oxygen entering the skin capillaries from external environment. By spinal vessel blood moves from the back end of the body to the front, and along abdominal vessel- in the opposite direction. An earthworm's blood is red. An iron-containing protein, similar to vertebrate hemoglobin and transporting oxygen, is found in a dissolved state in the blood plasma, and red blood cells are absent.

Nervous system more complex than that of flatworms and roundworms. It consists of peripharyngeal nerve ring with ganglia and abdominal nerve cord. This is the so-called nervous system ladder type. Suprapharyngeal paired ganglion performs the functions of the brain and is more developed than subpharyngeal. The nerve chain originates from the subpharyngeal node and consists of segmentally located pairs of ganglia, connected to each other by transverse and longitudinal commissures. Nerves extend from the ganglia to various organs. The earthworm's sense organs are poorly developed: there are no eyes or tentacles, but their skin contains numerous sensory cells and nerve endings.

Excretory organs presented segment by segment (i.e. in each segment) arranged in pairs metanephridia. They look like convoluted tubes and begin in the body cavity as a funnel with cilia. A channel departs from the funnel, which penetrates the transverse septum and passes into the cavity of the next segment. The terminal section of the metanephridium has an extension - bladder , which opens outward on the side of the worm’s body (i.e., in each segment there is a pair of very small excretory holes). In addition to metanephridia, the secretion involves chloragogenic cells, covering the surface of the intestine with a thin brown-yellow coating. Chlorogenic cells accumulate excretion products. Filled with metabolic products, these cells die, and their contents enter the body cavity, from where they are removed by metanephridia.

Reproduction. Earthworms hermaphrodites. The reproductive organs and girdle can be examined only during the breeding season - in the spring. To male

type Annelids Earthworm

the reproductive system includes two pairs of testes, located in segments 10 and 11, four vas deferens, which merge in pairs and open outwards paired male genital opening, located in the 15th segment. The female reproductive system includes pair of ovaries located in segment 13, oviducts, which open outwards in the 14th segment a pair of female genital orifices. There are two pairs in segments 9 and 10 spermatheca, each of which opens outward with an independent hole.

Earthworms reproduce sexually. Cross fertilization, in a cocoon. Two worms meet, tightly wrap their bodies around each other, attach their ventral sides to each other and exchange sperm, which ends up in the spermatic receptacles. After this, the worms disperse. Next, the belt forms a mucous muff, in which eggs are laid. As the coupling moves through the segments containing the spermatheca, the eggs are fertilized by sperm belonging to another individual. The muff is shed through the anterior end of the body, becomes compacted and turns into an egg cocoon, where young worms develop.

Regeneration. Earthworms are characterized by a high ability to regenerate, i.e. From each piece of the torn body of an earthworm, a whole worm is restored.

Questions for self-control

Name the aromorphoses of the annelid type.

Name the classification of the type Annelids.

What is the systematic position of the earthworm?

Where do earthworms live?

What body shape do earthworms have?

What is the body of an earthworm covered with?

What body cavity is characteristic of an earthworm?

What is the structure of the worm's digestive system?

What is the structure of the worm's circulatory system?

How does an earthworm breathe?

What is the structure of the worm's excretory system?

What is the structure of the worm's nervous system?

What structure does the reproductive system of an earthworm have?

How does an earthworm reproduce?

What is the significance of an earthworm?

type Annelids Earthworm

Rice. Earthworm, its passages in the ground and movement.

Rice. Internal structure of an earthworm.

1, 16 - intestine; 2 - partitions; 3 - epithelial lining of the secondary body cavity; 4 - dorsal (back) blood vessel; 5 - ring blood vessel; 6 - skin-muscle bag; 7 - cuticle; 8 - skin epithelium; 9 - whole; 10 - metanephridium; 11 - eggs; 12 - ring muscles; 13 - longitudinal muscles; 14 - ventral (abdominal) blood vessel; 15 - abdominal nerve cord.

type Annelids Earthworm

Rice. The structure of the anterior end of the earthworm's body.

The prostomium is the protrusion of the upper part of the first segment, covering the mouth. Peristomium is the name of the first segment of the body.

type Annelids Earthworm

Rice. The structure of an earthworm.

A - head end; B - internal structure; B - nervous system.

1 - mouth opening; 2 - male genital opening; 3 - female genital opening; 4 - belt; 5 - pharynx; 6 - esophagus; 7 - goiter; 8 - stomach; 9 - intestines; 10 - dorsal blood vessel; 11 - ring blood vessels; 12 - abdominal blood vessel; 13 - metanephridia; 14 - ovaries; 15 - testes; 16 - seed sacs; 17 - seminal receptacles; 18 - peripharyngeal nerve node; 19 - peripharyngeal nerve ring; 20 - abdominal nerve cord; 21 - nerves.

type Annelids Earthworm

Rice. Longitudinal section of the body of an earthworm.

1 - mouth; 2 - pharynx; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - intestine; 7 - peripharyngeal ring; 8 - abdominal nerve chain; 9 - “hearts”; 10 - dorsal blood vessel; 11 - abdominal blood vessel.