How do earthworms move? The role of the earthworm in nature. How does an earthworm work. Consider it from all sides. And what are worms for?
Ringed worms have the most high organization compared to other types of worms; they first have a secondary body cavity, circulatory system, more highly organized nervous system. At annelids inside the primary cavity, another, secondary cavity was formed with its own elastic walls of 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
A characteristic feature of the internal structure is that earthworms have developed real 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 rhythmically pulsate, 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
For most annelids, including earthworms, skin respiration is characteristic, 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 soils. sandy soils, where their skin soon dries up, and after the rains, when there is a lot of water in the soil, they crawl to the surface.
Nervous system
In the anterior segment of the worm there is a peripharyngeal ring - the largest accumulation 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 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 evolutionary development ancestors.
Earthworm
annelids have the following aromorphoses: 1. The body was divided into segments (metamers) with repeating sets internal organs. 2. A secondary cavity appeared - the whole, which has its own mesodermal lining. 3. There was a further complication of the nervous system: the concentration of nerve cells on the ventral side in each segment (the ventral nerve chain was formed), a significant increase in the brain ganglia (nodes) (supraglottic, subesophageal nerve ganglia, peripharyngeal ring). 4. A closed circulatory system arose, which ensured the rapid transport of substances throughout the body. 5. Respiratory organs appeared, which increased the respiratory surface and the intensity of gas exchange. 6. Made it harder digestive system: there was a differentiation of the middle intestine into sections, which led to step by step process digestion. 7. Parapodia formed - limbs for movement. 8. There was a further complication of the excretory organs: a metanephridial multicellular excretory system.
Earthworm – Lumbricus terrestris(type Annelids, class Small-bristle worms, Lumbricidae family) lives in moist, humus-rich soil. It feeds on organic matter, passing earth with plant debris through the intestines. Ch. Darwin also noted useful influence earthworms on soil fertility. Dragging the remains of plants into the mink, they enrich it with humus. Laying passages in the soil, they contribute to the penetration of air and water to the roots of plants.
Active earthworms during the warm season. In winter they hibernate. Freezing kills worms instantly, so they must burrow deeper into the ground where low temperatures do not penetrate. In spring, when the temperature reaches suitable value and the earth is soaked with rainwater, they have a mating season. They reproduce very quickly, producing about a hundred young worms a year. In summer, the worms are not so active. Food - dying plant residues - is very scarce at this time, and the soil is devoid of moisture, which can cause the death of worms. The autumn period is again characterized by the activity of worms. At this time, the reproduction of offspring begins again, which lasts until the onset of winter.
Earthworms live relatively long lives. Some manage to live for about ten years if they do not become victims of birds and moles. Another threat to their lives is the pesticides so widely used in horticulture today.
So, the Earthworm has an elongated, cylindrical body from 10 to 30 cm long. dorsal side more rounded, it is darker, a dorsal blood vessel shines through its skin. Abdominal side somewhat flattened and lighter colored. The anterior end of the body is thicker and darker colored. The body is made up of rings segments. In an adult worm, their number reaches 200. In the area of \u200b\u200b32-37 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 the segment-by-segment (i.e., in each segment) arrangement of a number of 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 the unevenness of the soil with them, the worm moves forward with the help of the muscles of the skin-muscular sac.
Covers. The body of an earthworm is covered skin-muscle sac. He is educated cuticle, single layer epithelium and two layers of muscles - external ring and internal longitudinal. The skin epithelium of the worm is rich mucous pieces of iron that produce slime covering the entire body of the worm and protecting it from drying out. The mucus also makes it easier to crawl in burrows by reducing friction on the soil.
Earthworm movement. When the worm crawls, waves of muscle contractions run through its body, and both the length and thickness of individual sections of its body are constantly changing. The movements produced by each part of the body consist in the fact that the segments that make up it are either stretched out and at the same time become thinner, then they contract and become thicker. As a result of such alternating extensions and contractions, the worm gradually moves forward: first, its head end is extended 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 sticks even further forward, and thus the further advancement of the worm continues (it is convenient to observe it by letting the worm crawl along the paper spread on the table).
body cavity. Inside the skin-muscular sac in annelids is located secondary cavity body, or in general. This body cavity is not limited by muscles, as in roundworms, but has its own epithelial(coelomic) pavement, i.e. inner side longitudinal muscles is 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 - dissipations. The secondary cavity is divided into chambers, each segment contains a pair of coelomic sacs. The coelomic fluid is under pressure and plays a role hydroskeleton, so the worm is elastic to the touch.
Digestive system consists of front, middle And rear guts. 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 gap. Due to the nutrition of rotting plant remains and humus, the digestive system has a number of features. Its anterior section is differentiated into a muscular throat, esophagus, goiter and muscular stomach. To increase the suction surface, a fold has formed on the upper part of the intestine typhlosol(typhlozolis). Please note: differentiated parts of the foregut - pharynx, esophagus, goiter, 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 integuments of the worm's body do not dry out, but excessive moisture (for example, very wet soil after rain) is just as detrimental to them.
Circulatory system closed, that is, the blood moves through the vessels without spilling into the body cavity. The movement of blood is determined by the pulsation large vessels, mainly encircling the esophagus. These are kind of hearts. Blood supplies all organs and tissues with nutrients, transporting them from the intestines, and oxygen entering the capillaries of the skin from external environment. By dorsal vessel blood moves from the back end of the body to the front, and along abdominal vessel- in reverse direction. The blood of an earthworm is red. An iron-containing protein, close to vertebrate hemoglobin and transporting oxygen, is contained in a dissolved state in the blood plasma, and erythrocytes are absent.
Nervous system more complex than that of flat and roundworms. It consists of nerve parapharyngeal ring with ganglia and abdominal nervous chains. This is the so-called nervous system ladder type. supraesophageal double ganglion performs the functions of the brain and is more developed than subesophageal. The nerve chain originates from the subpharyngeal node and is a segment-by-segment pairs of nerve nodes, connected to each other by transverse and longitudinal commissures. From the ganglia, nerves depart to various organs. The sense organs are poorly developed in the earthworm: eyes and tentacles are absent, but numerous sensory cells and nerve endings are embedded in their skin.
excretory organs are presented segment by segment (i.e., in each segment) by located paired metanephridia. They look like convoluted tubules, begin in the body cavity with a funnel with cilia. A channel departs from the funnel, which penetrates the transverse partition, passes into the cavity of the next segment. The final department of metanephridium has an extension - uric bubble, which opens outward on the lateral side of the body of the worm (i.e., each segment has a pair of very small excretory openings). In addition to metanephridia, the excretion involves chloragogenic cells covering the intestinal surface 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 the girdle can only be seen during the breeding season - in the spring. To male
type Annelids Earthworm
reproductive system include two pairs of testicles located in segments 10 and 11, four vas deferens, which merge in pairs and open outward doubles male sexual hole located in segment 15. The female reproductive system includes pair ovaries located in segment 13, oviducts, which open outward in segment 14 couple women's genital holes. There are two pairs in segments 9 and 10 seminal receptacles, each of which opens outwards with an independent opening.
Earthworms reproduce sexually. Cross fertilization, in a cocoon. Two worms meet, wrap their bodies tightly around each other, attach themselves to each other with their ventral sides and exchange sperm, which enters the spermatic receptacles. After that, the worms disperse. Further, the girdle forms a mucous sleeve, eggs are laid in it. When the clutch is advanced through the segments containing the seed receptacles, the eggs are fertilized by sperm belonging to another individual. The clutch is dropped through the front end of the body, 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 aromorphoses of the type Annelids.
Name the classification of the type Annelids.
What is systematic position 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 circulatory system of the worm?
How does he breathe earthworm?
What is the structure of the excretory system of the worm?
What is the structure of the worm's nervous system?
What structure does reproductive system earthworm?
How does an earthworm reproduce?
What is the significance of the earthworm?
type Annelids Earthworm
Rice. Earthworm, its moves in the ground and movement.
Rice. The internal structure of the earthworm.
1, 16 - gut; 2 - partitions; 3 - epithelial lining of the secondary body cavity; 4 - dorsal (back) blood vessel; 5 - annular blood vessel; 6 - skin-muscular sac; 7 - cuticle; 8 - skin epithelium; 9 - whole; 10 - metanephridium; 11 - eggs; 12 - circular muscles; 13 - longitudinal muscles; 14 - ventral (abdominal) blood vessel; 15 - abdominal nerve chain.
type Annelids Earthworm
Rice. The structure of the anterior end of the body of an earthworm.
The prostomium is a protrusion of the upper part of the first segment that covers the mouth. The peristomium is the name of the first segment of the body.
type Annelids Earthworm
Rice. The structure of the 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 - annular blood vessels; 12 - abdominal blood vessel; 13 - metanephridia; 14 - ovaries; 15 - testes; 16 - seed bags; 17 - seed receptacles; 18 - peripharyngeal ganglion; 19 - peripharyngeal nerve ring; 20 - abdominal nerve chain; 21 - nerves.
type Annelids Earthworm
Rice. Longitudinal section of the body of an earthworm.
1 - mouth; 2 - throat; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - gut; 7 - peripharyngeal ring; 8 - abdominal nerve chain; 9 - "hearts"; 10 - dorsal blood vessel; 11 - abdominal blood vessel.
Rice. Reproduction of the earthworm.
1 - mucous sleeve; 2 - cocoon; 3 - exit of young worms from the cocoon.
type annelids
Rice. Structure polychaete worm Nereids.
type annelids
Rice. Appearance Medical leeches.
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 prolonged droughts and 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.
Nutrition
Earthworms feed mainly on half-decayed plant remains. They drag, usually at night, leaves, stems and other things into their minks. Earthworms also feed on humus-rich soil, passing it through their intestines.
Circulatory system
The earthworm has a circulatory system that the hydra does not have. This system consists of two longitudinal vessels - dorsal and abdominal - and branches that connect these vessels and carry blood. The muscular walls of the vessels, contracting, drive blood throughout the body of the worm.
The blood of the earthworm is red, it is very important for the worm, as well as for other animals. 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. asexual reproduction he doesn't have. 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.
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
A characteristic feature of the internal structure is that earthworms have developed real 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 rhythmically pulsate, 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.
biouroki.ru
There are no special respiratory organs: they breathe the entire surface of the body. A thin cuticle and tenderness of the skin, a rich network of skin blood vessels provide the ability to absorb oxygen from environment. The cuticle is well wetted by water, and oxygen first dissolves in water. This entails the need to keep the skin moist.
Earthworms (lat. Lumbricidae) - a family of worms from the class of oligochaeta (Oligochaeta), a type of annelids (Annelida). Rather large worms (from 10 to 30 cm long) with thick skin, red blood and devoid of eyes belong to this family; each ring has two pairs of small hooked setae protruding from each side.
The genera and species of this family differ in the shape of the head dopa (the so-called upper lip), in the position of the girdle and in the number of rings; in Russia there are several species of earthworms from the genera: Lumbricus, Dendrobaena and Allolobophora.
Earthworms live in the earth, in which they dig long tubular passages; at night they come to the surface of the earth; they drag various organic remains into their passages - particles of leaves and other plant parts. They feed on decaying organic matter. The excrement of earthworms, containing many crushed earthen particles, is deposited by them on the surface of the earth. By this, earthworms contribute to an increase in the arable layer of the earth, while at the same time they loosen the soil with their burrows, and by pulling out plant residues increase its content with organic parts.
The importance of earthworms in the process of soil formation was first pointed out by Darwin.
Fertilization takes place at night, on the surface of the earth, and takes place mutually; both individuals tightly adjoin each other, turning around with opposite ends, and the seed of one individual flows into the seed receivers of the other; at the same time, both individuals are interconnected by a ring formed by the secretion of special glands of the so-called girdle; at the end of the act, the ring is discarded.
Earthworms are used as bait for fishing.
answer.mail.ru
There are no special respiratory organs: they breathe the entire surface of the body.
1058; A thin cuticle and tenderness of the skin, a rich network of skin blood vessels provide the ability to absorb oxygen from the environment. The cuticle is well wetted by water, and oxygen first dissolves in water.
1069; This entails keeping the skin moist.
09mog.ru
Features and habitat
Earthworm , he is ringed - a well-known resident on any personal plot. And it would seem, absolutely imperceptible, useless creation.
However, any person, at least somehow connected with the earth, will be very happy with such inhabitants of his garden. IN Russian Federation there are no more than a hundred species of earthworm. But all over the world there are one and a half thousand varieties of them.
It belongs to the family of annelid worms, low-bristle class. Its entire long body consists of many rings. There may be seventy, or there may be three hundred. Since in length it grows more than twenty-five centimeters.
But there are also the smallest, two or three centimeters. The Australian earthworms reach two and a half meters in size. Its color is literally gray-brown - raspberry.
Also, on each ring, or it is also called a segment, there are bristles. In our ordinary garden worms, as a rule, eight bristles grow. They are classified as low-bristle.
However, there are also tropical polychaete species worms, in which the villi grow in dozens. The bristles help the worms crawl along absolutely all soil tubercles or burrow into holes.
You can find them by taking the worm in your hands and swiping your finger from back to front. But since it is difficult for an inexperienced person to determine where his butt is, you can simply lightly run your hand along the body and back. You can immediately feel it. In one direction, the worm will be absolutely smooth, and in the opposite direction, it will be rough.
Anyone who has ever taken a worm in his hands knows that he is covered with not very pleasant mucus, which is vital for him. Firstly, mucus helps the invertebrate to move freely in the ground. Secondly, since the worm does not have lungs, it breathes through the skin. And thanks to the moisture on the mucus, the body is saturated with oxygen.
Samo earthworm body, consists of two groups of muscle tissue. They are longitudinal and transverse. The transverse muscles are under protective top layer worm skin.
With their help, the worm becomes as long as possible. And the stronger muscles are longitudinal. They shorten, reduce the body. So, sometimes lengthening, sometimes shortening, the animal moves.
The earthworm belongs to the secondary cavity animals. Therefore, it has a complete closed circulatory system. Because they are active.
Muscles contract many times more often than in primary cavity worms. To do this, they need blood to provide the worm with all nutrients and oxygen.
IN earthworm structure there are a pair of blood vessels, one of them is called the dorsal, the second abdominal. Ring vessels connect them together. Blood flows through them from back to front, and vice versa.
In each ring, or as it is also called, a segment, there is a pair of tubules. The funnels at their ends open and feces are discharged through the bottom. earthworm. This is how the excretory system works.
As for the nervous system, it is nodal. Its components are the ventral nerve chain and the peripharyngeal nerve ring. These endings consist of fibers, and those, in turn, respond to the urges of the contracted muscles of the worm. Thanks to them, the worm can eat, purposefully move, multiply, and develop.
In the building earthworm organs, there are no those responsible for smell, touch, sight, sensation. But there are certain cells, they are located along the entire body of the invertebrate. With their help, the worm navigates in the dark and impenetrable land.
Character and lifestyle
Even Charles Darwin suggested that earthworms have intelligence. Watching them, he noticed that when he dragged a dry leaf into his dwelling, it was turned with its narrow side. This facilitates the passage of the leaf through a dense, earthy hole. But spruce needles, on the contrary, take it as a base so that they do not bifurcate.
All day, all rain life worm scheduled by the minute. He now and then climbs in the ground, makes moves, swallowing it. The worm digs holes in two ways. He or, as already mentioned, swallows the earth, gradually moving forward.
If the ground is too hard. And then leaving their biological waste. Or, he pushes it with his refined end, in different directions, and makes moves for himself. The passages are obliquely vertical.
Tek same, rain worm, hunting in soil, drags into its holes, for insulation, various leaves, veins from leaves, thin pieces of paper and even shreds of wool. Its burrows are up to one meter deep. And the worms are larger in size, and all ten meters. The worm works mainly at night.
BUT why earthworms come to the surface in great numbers. This means he can't breathe. This usually happens after heavy rains. The earth is clogged with moisture, and there is no oxygen at all. Upon the arrival of cold earthworm goes deep into the soil.
Earthworm food
The food of the worm is quite typical. swallowing in large quantities earth along with food. For food, they are suitable for wilted and slightly rotten leaves, mushrooms. But she shouldn't have bad smell otherwise the worm won't eat it.
It turns out that earthworms even build whole pantries for themselves, and put food there for the winter. They eat it only in case of critical need. For example, in winter time when the ground is completely frozen, and there can be no talk of any terrestrial food.
Having sucked food together with a clod of earth, through the pharynx, with muscular movements, then expanding his body, then narrowing, he pushes it to the back of the esophagus into the goiter. After, it enters the stomach. From the stomach it is sent to be overetched in the intestines, thanks to enzymes, it comes out with the most useful biomass.
Making moves, and at the same time snacking, rainy worm necessary crawl out periodically to the surface to throw off the ground. At the same time, he adheres to the hole with his edge of the tail, as if holding on to it.
And after, there are always earthen slides. The soil processed by the worm turns out to be sticky. Notice it dries up, and becomes small, with a match head balls.
These balls are saturated with vitamins, enzymes, organic substances, which, as a result, kill all bacteria in the ground, prevent decay, which is very important for plant roots. And they also act on the composition of the earth as an antiseptic, disinfecting it.
Reproduction and lifespan
Earthworms can be of different sexes, and hermaphrodites. All earthworms have thickenings on the front third of their body. They contain the ovary and testis. Hermaphrodites let the seed into each other. Already mature testicles, within ten pieces, are inseminated. And crawl away in different directions.
When a female is ready for reproduction, she approaches her partner and copulates. Something like a cocoon is formed on it, consisting of several dozen thickened segments.
It is separated by a kind of belt. This cocoon receives all the nutrients necessary for the brood. After fertilization, the worm removes this burden from itself, it simply slides off the animal.
The edges on the cocoon, on both sides, are quickly pulled together so that future offspring do not dry out before they are born. Then, throughout four weeks small worms ripen and hatch.
Once born, they spread in all directions. And already from the first days of their lives, they begin active work, processing the land. And already at the age of three months, grown children reach the size of adults.
Another fact about earthworms is the ability to regenerate. If someone or something divides it into two halves. Over time, each of the halves will become a full-fledged individual. This is one of the ways of reproduction, but not sexually.
The role of the earthworm very important in agriculture. Firstly, they saturate the soil with oxygen, which is so necessary for everything growing on it. With their moves, they help the roots to fully develop.
Moisture is evenly distributed, and the soil is well ventilated, loosened. Due to the constant movement of the earth, with the help of worms, stones are extracted from it.
Also, with their recycled sticky residues, they stick the soil together, preventing it from eroding. Well, of course, they fertilize the earth when they drag leaves, insect larvae into it. It all rots and serves as excellent, natural bio-additives.
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Variety of worms
The Worms type includes a group of multicellular animals that have an elongated body and no skeleton. Habitats are usually wet soil, sea and fresh water. They can range in size from those that can only be seen with a microscope to large forms, several meters long. In accordance with the shape of the body, there are: Flat, Round and Annelids. All types have three body layers. Germ layers - ectoderm, endoderm and mesoderm give rise to the development of all their tissues and organs.
The brightest and most famous representatives of flatworms: planaria, liver fluke, pork and bovine tapeworms, echinococci, schistosomes, etc. Known annelids include: earthworm, oligochaete worms, leeches and misostomids. Round protostomes are represented by well-known roundworms, pinworms, rishts, trichinella, etc.
Despite the diversity existing species worms, their types, structural features, methods of reproduction, nutrition, habitats, etc., there are a considerable number of similarities that are characteristic of all of them. For example, the respiration of flatworms, divided into aerobic and anaerobic, depending on the habitat, is also characteristic of the other two types.
flatworms
The organ system of flatworms is represented by a number of main structural components, united by common functional features and by type of structure. The main systems include: respiratory, reproductive, excretory, muscular, nervous and integumentary.
Previously, a number of other taxonomic elements were attributed to the class of ciliated protostomes, characterized by worm-like forms, the absence of body cavities, and were considered invertebrates.
The body shape of any type has a bilaterally symmetrical shape, in which the head and tail ends are expressed, both ends are slightly flattened, however, in large species, flattening is strongly pronounced. The organ system of flatworms for respiration and circulation is absent. The cavity in the body does not develop, but this is true for all representatives, except for tapeworms and flukes in certain life cycles.
The structure of the integument of the body
Getting to know the muscles
The muscle tissues of flatworms are represented by a muscular sac that lies under the epithelium. It consists of a number of layers of muscle-type cells that are not divided into muscles. However, some differentiation is observed in the areas of the pharynx and reproductive system. The outer part of the cells of the muscle layers are oriented across, and the inner ones along the posterior-anterior axis of the body. The outer musculature is called the annular layer, and the inner one is called the longitudinal musculature layer.
Breathing methods
All groups of flatworms are characterized by the presence of a pharynx that leads to the intestine. The exceptions are cestodes and tapeworms. This intestine opens into the parenchyma intended for digestion, blindly closes and is connected with the outside world only through the mouth opening. Some large turbellarians have anal pores in their presence, however, this is an exception only for some members of the species. Small forms are characterized by a straight intestine, while large ones (planarian, fluke) may have a branched one. The pharynx is located on the surface of the abdomen, often it can be found in the middle or closer to the back of the body. In some groups of worms, the pharynx moves forward.
Features of the nervous system and sensory organs
When characterizing the nervous system of flat protostomes, it is worth noting that they are characterized by the presence of nerve nodes located in front of the body, and there are also brain ganglia and nerve columns branching from them, which are connected by jumpers. Sensitive organs include individual skin cilia, which are outgrowths of cells nervous type. There are free-living species that have special light-sensitive eyes of a pigmented nature. Such organs serve as a primitive adaptation to the sense of balance and allow you to see, albeit primitively.
Selection system
Flat worms have an excretory system that takes the form of protonephridia. With their help, the process of osmoregulation and metabolism proceeds. The selection system takes the form of channels that branch and combine into 1-2 channels. Initially, these are stellate-type cells, which, branching into tubules, open a gap in themselves for the passage of a bundle of flagella. Merging, the tubules form a larger structure and are excreted in the form of excretory pores on the surface of the body. Such excretion systems are called protonephridial. Metabolic products dangerous for the life of the worm are excreted along with the liquids through the aforementioned protonephridia, as well as with the help of special cells parenchyma - atrocytes, which play the role of "storage kidneys".
Reproduction
- Germary - is actually the ovary. Produces eggs, poor in yolk, but capable of development.
- Vitellaria - sometimes called yolk, it produces abortive-type eggs, they are rich in yolk.
These composite reproductive systems form complex, or exolecithal, eggs. The common shell may contain one egg or a number of yolk balls secreted by accessory glands.
Conclusion
Summing up the above text, several conclusions can be made, among which the most significant are: the respiration of flatworms is carried out by the surface of the whole body, mainly flatworms are predators, there is a muscular sac, the body cover is represented by a tegument, most are hermaphrodites and only a few of them are dioecious.
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annelids have the following aromorphoses: 1. The body was divided into segments (metamers) with repeating sets of internal organs. 2. A secondary cavity appeared - the whole, which has its own mesodermal lining. 3. There was a further complication of the nervous system: the concentration of nerve cells on the ventral side in each segment (the ventral nerve chain was formed), a significant increase in the brain ganglia (nodes) (supraglottic, subesophageal nerve ganglia, peripharyngeal ring). 4. A closed circulatory system arose, which ensured the rapid transport of substances throughout the body. 5. Respiratory organs appeared, which increased the respiratory surface and the intensity of gas exchange. 6. The digestive system became more complicated: the midgut was differentiated into sections, which led to a gradual process of digestion. 7. Parapodia formed - limbs for movement. 8. There was a further complication of the excretory organs: a metanephridial multicellular excretory system was formed.
Earthworm – Lumbricus terrestris(type Annelids, class Small-bristle worms, Lumbricidae family) lives in moist, humus-rich soil. It feeds on organic matter, passing earth with plant debris through the intestines. Even C. Darwin noted the beneficial effect of earthworms on soil fertility. Dragging the remains of plants into the mink, they enrich it with humus. Laying passages in the soil, they contribute to the penetration of air and water to the roots of plants.
Earthworms are active in the warm season. In winter they hibernate. Freezing temperatures kill 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 value and the ground is saturated with rainwater, they have a mating season. They reproduce very quickly, producing about a hundred young worms a year. In summer, the worms are not so active. There is very little food - dying plant residues - at this time, and the soil is devoid of moisture, which can cause the death of worms. The autumn period is again characterized by the activity of worms. At this time, the reproduction of offspring begins again, which lasts until the onset of winter.
Earthworms live relatively long lives. Some manage to live for about ten years if they do not become victims of birds and moles. Another threat to their lives is the pesticides so widely used in horticulture today.
So, the Earthworm has an elongated, cylindrical body from 10 to 30 cm long. dorsal side more rounded, it is darker, a dorsal blood vessel shines through its skin. Abdominal side somewhat flattened and lighter colored. The anterior end of the body is thicker and darker colored. The body is made up of rings segments. In an adult worm, their number reaches 200. In the area of \u200b\u200b32-37 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 the segment-by-segment (i.e., in each segment) arrangement of a number of 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 the unevenness of the soil with them, the worm moves forward with the help of the muscles of the skin-muscular sac.
Covers. The body of an earthworm is covered skin-muscle sac. He is educated cuticle, single layer epithelium and two layers of muscles - external ring and internal longitudinal. The skin epithelium of the worm is rich mucous pieces of iron that produce slime covering the entire body of the worm and protecting it from drying out. The mucus also makes it easier to crawl in burrows by reducing friction on the soil.
Earthworm movement. When the worm crawls, waves of muscle contractions run through its body, and both the length and thickness of individual sections of its body are constantly changing. The movements produced by each part of the body consist in the fact that the segments that make up it are either stretched out and at the same time become thinner, then they contract and become thicker. As a result of such alternating extensions and contractions, the worm gradually moves forward: first, its head end is extended 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 sticks even further forward, and thus the further advancement of the worm continues (it is convenient to observe it by letting the worm crawl along the paper spread on the table).
body cavity. Inside the skin-muscular sac in annelids is located secondary cavity body, or in general. This body cavity is not limited by muscles, as in roundworms, but has its own epithelial(coelomic) pavement, i.e. the inner side of the longitudinal muscles is 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 - dissipations. The secondary cavity is divided into chambers, each segment contains a pair of coelomic sacs. The coelomic fluid is under pressure and plays a role hydroskeleton, so the worm is elastic to the touch.
Digestive system consists of front, middle And rear guts. 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 gap. Due to the nutrition of rotting plant remains and humus, the digestive system has a number of features. Its anterior section is differentiated into a muscular throat, esophagus, goiter and muscular stomach. To increase the suction surface, a fold has formed on the upper part of the intestine typhlosol(typhlozolis). Please note: the differentiated parts of the foregut - pharynx, esophagus, goiter, 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 integuments of the worm's body do not dry out, but excessive moisture (for example, very wet soil after rain) is just as detrimental to them.
Circulatory system closed, that is, the blood moves through the vessels without spilling into the body cavity. The movement of blood is determined by the pulsation of large vessels, mainly encircling the esophagus. These are kind of hearts. Blood supplies all organs and tissues with nutrients, transporting them from the intestines, and oxygen entering the capillaries of the skin from the external environment. By dorsal vessel blood moves from the back end of the body to the front, and along abdominal vessel- in the opposite direction. The blood of an earthworm is red. An iron-containing protein, close to vertebrate hemoglobin and transporting oxygen, is contained in a dissolved state in the blood plasma, and erythrocytes are absent.
Nervous system more complex than that of flat and roundworms. It consists of nerve parapharyngeal ring with ganglia and abdominal nervous chains. This is the so-called nervous system ladder type. supraesophageal double ganglion performs the functions of the brain and is more developed than subesophageal. The nerve chain originates from the subpharyngeal node and is a segment-by-segment pairs of nerve nodes, connected to each other by transverse and longitudinal commissures. From the ganglia, nerves depart to various organs. The sense organs of the earthworm are poorly developed: eyes and tentacles are absent, but numerous sensory cells and nerve endings are embedded in their skin.
excretory organs are presented segment by segment (i.e., in each segment) by located paired metanephridia. They look like convoluted tubules, begin in the body cavity with a funnel with cilia. A channel departs from the funnel, which penetrates the transverse partition, passes into the cavity of the next segment. The final department of metanephridium has an extension - uric bubble, which opens outward on the lateral side of the body of the worm (i.e., each segment has a pair of very small excretory openings). In addition to metanephridia, the excretion involves chloragogenic cells covering the intestinal surface 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 the girdle can only be seen during the breeding season - in the spring. To male
type Annelids Earthworm
reproductive system include two pairs of testicles located in segments 10 and 11, four vas deferens, which merge in pairs and open outward doubles male sexual hole located in segment 15. The female reproductive system includes pair ovaries located in segment 13, oviducts, which open outward in segment 14 couple women's genital holes. There are two pairs in segments 9 and 10 seminal receptacles, each of which opens outwards with an independent opening.
Earthworms reproduce sexually. Cross fertilization, in a cocoon. Two worms meet, wrap their bodies tightly around each other, attach themselves to each other with their ventral sides and exchange sperm, which enters the spermatic receptacles. After that, the worms disperse. Further, the girdle forms a mucous sleeve, eggs are laid in it. When the clutch is advanced through the segments containing the seed receptacles, the eggs are fertilized by sperm belonging to another individual. The clutch is shed through the front end of the body, 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 aromorphoses of the type Annelids.
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 circulatory system of the worm?
What is the structure of the excretory system of the worm?
What is the structure of the worm's nervous system?
What is the structure of the reproductive system of an earthworm?
How does an earthworm reproduce?
What is the significance of the earthworm?
type Annelids Earthworm
Rice. Earthworm, its moves in the ground and movement.
Rice. The internal structure of the earthworm.
1, 16 - gut; 2 - partitions; 3 - epithelial lining of the secondary body cavity; 4 - dorsal (back) blood vessel; 5 - annular blood vessel; 6 - skin-muscular sac; 7 - cuticle; 8 - skin epithelium; 9 - whole; 10 - metanephridium; 11 - eggs; 12 - circular muscles; 13 - longitudinal muscles; 14 - ventral (abdominal) blood vessel; 15 - abdominal nerve chain.
type Annelids Earthworm
Rice. The structure of the anterior end of the body of an earthworm.
The prostomium is a protrusion of the upper part of the first segment that covers the mouth. The peristomium is the name of the first segment of the body.
type Annelids Earthworm
Rice. The structure of the 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 - annular blood vessels; 12 - abdominal blood vessel; 13 - metanephridia; 14 - ovaries; 15 - testes; 16 - seed bags; 17 - seminal receptacles; 18 - peripharyngeal ganglion; 19 - peripharyngeal nerve ring; 20 - abdominal nerve chain; 21 - nerves.
type Annelids Earthworm
Rice. Longitudinal section of the body of an earthworm.
1 - mouth; 2 - throat; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - gut; 7 - peripharyngeal ring; 8 - abdominal nerve chain; 9 - "hearts"; 10 - dorsal blood vessel; 11 - abdominal blood vessel.
Rice. Reproduction of the earthworm.
1 - mucous sleeve; 2 - cocoon; 3 - exit of young worms from the cocoon.
type annelids
Rice. The structure of the polychaete worm Nereid.
type annelids
Rice. Appearance of a medical leech.
Earthworm belongs to the group of annelids. He doesn't have any special bodies, designed specifically for gas exchange, and gas exchange occurs by diffusion through 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 so much oxygen.
However, in annelids there is a circulatory system (unlike some simpler animals and unicellular organisms), and the respiratory pigment hemoglobin is dissolved in their blood. Contractions of large blood vessels drive the blood along with the 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 the 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.
A. Locust tracheal system. B. The structure of the trachea of an insect.Respiratory system of insects - locusts.
In insects, gas exchange carried out through a system of tubes, the so-called trachea. Such a system allows oxygen to flow from the air directly to the tissues and there is no need to transport it through the blood. It's much more fast way than the diffusion of dissolved oxygen through tissues; such gas exchange creates conditions for a high metabolic rate.
spiracles- paired openings on the second and third thoracic and on the first eight abdominal segments of the insect's body lead to the air cavities. Branched tubes - tracheas - depart from these cavities. Each trachea is lined with epithelium secreting a thin layer of chitinous material. Usually this rigid 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 segment of the body, the tracheae branch 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 flying muscles, they end blindly inside individual cells. The degree of branching of the tracheoles can vary depending on the metabolic needs of the tissues.
chitin lining in tracheoles missing. At rest, they are filled with a watery fluid; at this time, oxygen diffuses through them to the tissues (and CO 2 - in the opposite direction) at a rate that is quite sufficient to meet 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 is partially absorbed into the tissues by osmotic forces, and more air enters the tracheoles, and therefore more oxygen, and this oxygen is supplied directly to the tissues just when they need it.
Conditions created in the tissues of an insect at rest and in an active state (work of the tracheoles).
The total flow of air passing through the body of an insect is regulated by a mechanism closing spiracles. The opening of each spiracle is equipped with a system of valves controlled by very small muscles. The edges of this hole 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 body of the insect.
Increased activity leads to increased formation of CO 2 . Chemoreceptors catch it and the spiracles open. The same stimulus can also cause ventilation movements of the body, especially in large insects such as locusts. The dorsoventral muscles, contracting, make the body of the insect flatter, as a result of which the volume of the tracheal system decreases and air is pushed out of it (“exhalation”). The suction of air ("inhalation") occurs passively, when the segments of the body, due to their elasticity, take their original shape.
According to some data, thoracic and abdominal spiracles open and close alternately, and this, combined with the ventilation movements of the body, creates a unidirectional airflow that enters the body of the insect 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 is determined in most insects solely by the diffusion of oxygen through the tissues of the insect. Diffusion, on the other hand, is known to be effective only at short distances, and this imposes severe limits on the size that insects can reach. These small distances, at which diffusion is sufficiently effective, do not exceed 1 cm; therefore, although insects up to 30 cm long are found, their body should not be more than 2 cm thick.