Angina

What leeches can treat? External and internal structure of a leech. Features of the external structure of leeches.

ABSTRACT

On the topic: "Leeches".

1) History of the leech

2) Characteristics of a leech

3) Types of leeches

4) Leeches in medicine. Hirudotherapy

1) History of the leech

The history of the leech goes back to ancient times. Even in time immemorial, our distant ancestors recognized the unique healing properties of this animal. The first information about the use of leeches with medical purposes belong to Ancient Egypt. Fragments of wall paintings depicting treatment with leeches were discovered in the tomb of the pharaohs of the 18th dynasty (1567-1308 BC). At its dawn, medicine saw leeches as a panacea, a remedy for almost all diseases. In the East, leeches were used by the great scientist and healer Abu Ali Ibn Sina (Avicenna), who dedicated an entire section to them in his book “The Science of Healing.” IN Ancient Rome The famous physician Claudius Galen treated people with leeches. Leeches were also used in Ancient Greece. The Greek name for the leech “geruda” has survived to this day - in modern medicine, treatment with leeches is called gerudotherapy.

The most ancient species in origin - Acanthobdella peledina - occupies an intermediate position between oligochaete worms and leeches. Traveling through Siberia in 1842-1845, the outstanding Russian naturalist Alexander Fedorovich Middendorf discovered these then unknown worms on peled. Having fixed them in a special solution, he sent them to his colleague, a great expert on annelids, the Swiss zoologist E. Grube. The scientist described them and assigned them to the new genus Asapthobdella. In Russia, leeches were once revered much more than many medicines. The leech industry also flourished. Up to 70 million little saviors were taken to countries every year Western Europe, especially to Germany and France, and one piece cost 10 kopecks (for comparison: a chicken could be bought for 20 kopecks). The famous Russian doctor Pirogov during the Crimean War of 1854 daily administered from 100 to 300 leeches to wounded soldiers in Sevastopol.

2) Characteristics of a leech

Leeches (Hirudinei) are a detachment of the class of annelids. The body is elongated or oval, more or less flattened in the dorso-ventral direction, clearly divided into small rings, which, 3-5 in number, correspond to one body segment; there are numerous glands in the skin that secrete mucus; at the posterior end of the body there is usually a large sucker; often at the anterior end there is a well-developed sucker, in the center of which the mouth is placed; more often the mouth is used for suction. At the anterior end of the body there are 1 - 5 pairs of eyes, located in an arc or in pairs one behind the other. Powder on the dorsal side above the posterior sucker.

Nervous system consists of a two-lobed suprapharyngeal ganglion or brain, connected to it by short commissures under the pharyngeal node (derived from several fused nodes of the abdominal chain) and the abdominal chain itself, located in the abdominal blood sinus and having about 20 nodes. The head node innervates the sensory organs and the pharynx, and from each node of the abdominal chain there are 2 pairs of nerves, and the corresponding body segments that nerve them; the lower wall of the intestine is equipped with a special longitudinal nerve that gives branches to the blind sacs of the intestine.

The digestive organs begin with a mouth armed either with three chitinous serrated plates (jaw leeches - Gnathobdellidae), which serve to cut through the skin when sucking blood in animals, or a proboscis capable of protruding (in proboscis leeches - Rhynchobdellidae); Numerous salivary glands open into the oral cavity, sometimes secreting a poisonous secretion; the pharynx, which plays the role of a pump during sucking, is followed by an extensive, highly extensible stomach, equipped with lateral sacs (up to 11 pairs), of which the posterior ones are the longest; the hindgut is thin and short.

The circulatory system consists partly of real, pulsating vessels, partly of cavities - sinuses, which represent the remainder of the cavity (secondary) of the body and are connected to each other by ring canals; The blood of proboscis leeches is colorless, while that of jawed leeches is red, due to hemoglobin dissolved in the lymph. Only the river has special respiratory organs. Branchellion, shaped like leaf-like appendages on the sides of the body.

Excretory organs are arranged according to the type of metanephridia or segmental organs of annelids and most leeches have a pair of them in each of the middle segments of the body. Leeches are hermaphrodites: Most male genital organs consist of vesicles (testes), a pair in 6 - 12 middle segments of the body, connected on each side of the body by a common excretory duct; these ducts open outward with one opening lying on the ventral side of one of the anterior rings of the body; The female genital opening lies one segment behind the male and leads into two separate oviducts with sac-like ovaries. Two individuals copulate, each simultaneously playing the role of a female and a male. During the laying of eggs, leeches are secreted by glands located in the genital area, thick mucus, surrounding in the form of a cover middle part P.'s body, eggs are laid in this case, after which P. crawls out of it, and the edges of its holes come together, stick together and thus form a capsule with eggs inside, usually attached to bottom surface seaweed sheet; The embryos, leaving the egg shell, sometimes (Clepsine) remain for some time on the underside of the mother’s body. All P. are predators, feeding on the blood of mostly warm-blooded animals, or mollusks, worms, etc.; they live mainly in fresh waters or in wet grass; but there are also marine forms (Pontobdella), just as there are terrestrial forms (in Ceylon).

Thanks to hirudin and other substances secreted by the salivary glands, blood can remain in a liquid state in the leech’s stomach for months without rotting.

3) Types of leeches

Surveyor leech - Piscicola geometra. 1-5 cm in length. Thin round body with a very large rear sucker. Swims in water (fresh and brackish) or stays on plants, lying in wait for fish, whose blood it feeds on. When a fish appears, the leech begins searching movements. During mass reproduction they harm fisheries, causing blood loss in fish and transmitting the causative agent of abdominal dropsy. After mating, which occurs on the host fish, both leeches (hermaphrodites) lay up to 90 cocoons on aquatic plants.

Common leech, or false horse leech, Haemopis sanguisuga. About 10 cm in length. Common in ponds, rivers and ditches; goes ashore. Predator. Attacks any animal it can overcome, such as earthworms. Cocoons are laid in moist soil on the shore. widespread in water bodies of Russia, Ukraine, Belarus, Moldova, and the Caucasus. But, unlike the medical one, it is painted in gray-black tones and does not have orange-red spots. This leech is not a bloodsucker - it either swallows its prey whole or tears off pieces from it. If you set out to fatten the false horse leech, you can grow a specimen up to 40 centimeters long. A strong voracious predator eats worms (including other leeches), mollusks, larvae of aquatic insects, tadpoles, and sometimes small fish. It is very easy to distinguish them from other leeches: their front sucker is sharply separated from the rest of the body and usually has the shape of a disk or cup, which helps it securely attach to the fish. In most species, two pairs of eyes are located on the anterior sucker, and there are often eye-like points on the posterior one.

Medical leech - Hirudo medicinalis. The largest (more than 20 cm in length) leech in Europe. Found in lakes, ponds, swamps; Currently, not as often as before, but again there is a slight increase in numbers. Young leeches feed on larvae and worms, while adults suck the blood of vertebrates (especially mammals) and can, having pumped to the limit, go without food for more than a year. Cocoons are laid in damp coastal soil. Leeches, like oligochaetes, are hermaphrodites and are similar to them in their reproductive features (they lay cocoons through the girdle); however, their ability to regenerate is much lower and they reproduce only sexually. Medical leeches were previously widely used mainly for bloodletting.

Currently, the scale of medicinal use of medicinal leeches is increasing again.

Eight-eyed leech - Herpobdella octoculata. Up to 6 cm in length, rather flat. It is common in stagnant or slow-flowing bodies of water, and can tolerate even severe pollution. Attacks various (living and dead) insect larvae, mainly bell-bellied mosquitoes, and other small animals. It lays its brown cocoons on stones, plants, etc.

The flattened leech - Glossiphonia complanata. 1-3 cm in length. Transparent; The color may be different, but the dorsal side is greenish or brownish. Lives in standing and flowing bodies of water; on plants and stones. It attaches mainly to lung snails, but also attacks worms and insect larvae. Shows care for the offspring, carrying a cocoon and young leeches.

Pond leech - Helobdella stagnalis. Up to 1 cm in length. Easily recognized by the dark round plate on the back between the 12th and 13th segments. It is found everywhere: on plants and stones, in standing and flowing bodies of water. Sucks out small animals (worms, isopods, molluscs and insect larvae, such as mosquito larvae).

Asapthobdellaoccupies intermediate position between oligochaete worms and leeches. This leech attacks salmon fish and graylings. It lives in freshwater bodies of northern Europe and Asia, from Norway to Kolyma, and its southernmost location is Lake Onega.

On fish, these leeches appear in late spring or early summer, when they weigh only 5-10 milligrams, but by the beginning of winter, when the worms reach sexual maturity and their weight is more than 200 milligrams, they leave the victim. Their further fate is unknown. Most likely, worms reproduce and develop in small places overgrown with plants. But no one has yet caught these leeches in a free state and observed how they reproduce and develop, although for some time it was possible to keep them in aquariums.

In Russian water bodies, with the exception of the European northeast and Western Siberia, the flat leech Hemiclepsis marginata is widespread. The length of its body is 30 millimeters with a width of 7. In calmly sitting leeches the body is flat and short, but in stretched ones it becomes very long, and in this position they can be mistaken for an ordinary fish leech. The dorsal side of the body is convex, the ventral side is slightly concave. The color is variegated, greenish-brown, and greenish-blue in young ones. There are seven longitudinal rows of yellow spots along the dorsal side of the body; there are also yellow spots on the rear sucker. These leeches suck blood not only from fish, but also from amphibians (newts, frogs).

Like all flat leeches, N. marginata takes care of its offspring. The mother leech covers with her body the thin-walled, shapeless cocoons she lays, which contain many eggs. After hatching, the young are attached to the mother's belly and move with her. In case of danger, the leech stops moving, protecting the offspring with its body. Growing up, the juveniles begin to live independently - initially temporarily, and later permanently.

Another representative of flat leeches - the snail leech (Glossiphonia complanata) - is not an enemy of fish, but also causes damage to aquarium farming. Its victims, as the name suggests, are mollusks, so aquarists who collect, in addition to fish, various snails, should know it well by sight, especially since it ends up in the aquarium (with plants, soil, etc.) more often other of its relatives and remains unnoticed longer.

The body length of the snail leech rarely exceeds 20 millimeters, and the color is greenish-brown. Due to the fact that her body is translucent, it is easy to see internal organs and the whole process of bearing offspring.

The snail leech cannot swim and moves by crawling. She is extremely lazy and spends a lot of time lying motionless, clinging to underwater objects or plants. It is not easy to tear it away from the substrate, and if it succeeds, it curls up into a ball like a hedgehog.

Clepsiue tesselata - Tatar leech, with a broad oval body, greenish-brown color, with several rows of warts on the back and 6 pairs of triangular eyes located one after the other; lives in the Caucasus and Crimea, where it is used by the Tatars for medicinal purposes;

The leech Cystobranchus fasciatus, which poses a danger to fish, lives in the Dnieper, Volga, Urals, and Kura. Its elongated body reaches a length of 75 millimeters with a width of 8. The rear sucker is very large; the eye-like spots on it, like those of the common fish leech, are located between radial pigment stripes. The body color is gray with a violet tint; against this background, wide dark gray transverse stripes with blurred edges stand out.

In reservoirs Leningrad region lives the leech C. respirans, which is also very undesirable in an aquarium. Its body is relatively short (up to 40 millimeters with a width of 10), grayish-yellow, completely dotted with small brown age spots.

4) Leeches in medicine. Hirudotherapy

It is known that a leech, when clinging to the skin of a person or animal, quietly bites through it and sucks out a small amount of blood, up to about 10-15 ml. This bloodletting with the help of leeches was considered a universal means of treatment. It was used for diseases of the heart, liver, lungs, stomach, eyes, tuberculosis and many other ailments. The famous healer Hippocrates, whose oath all young doctors take upon receiving their diploma, said: “The doctor heals, Nature heals.” The leech is precisely part of nature, its small but very effective doctor.

Later it turned out that the point is not that the leech sucks out a little of the patient’s blood, but that its saliva, which enters the human body, has unique healing properties. It contains more than 60 biologically active substances who are able to cope even with severe diseases. A special protein substance, hirudin, is injected into the wound of the leech, which prevents blood clotting. If hirudin were not released, damaged vessels would quickly become clogged blood clots which prevents blood from being sucked out

There are about 400 species of leeches in the world. There are only two of them in Russia: the medicinal leech (Hirudo medicinalis) and the Nile leech (Limnatis nilotica), usually called the horse leech. Leeches are found in ponds, lakes and quiet rivers in central and southern Russia. They are also widespread abroad. Leeches love clean, running water, but they are also found in damp places near water - in clay, damp moss, where they can remain alive for months and even years. But if during a drought they do not have time to burrow into the wet soil, they will inevitably die.

Only medicinal leech is suitable for use in medicine. It comes in black, dark gray, dark green, green, and red-brown colors. She has six stripes on her back - red, light brown, yellow or black. The sides are green with a yellow or olive tint. The abdomen is motley: yellow or dark green with black spots.

On its head, the leech has ten small eyes arranged in a semicircle: six in front and four in the back, on the back of the head. At the narrower end of the body is the head, at the other is the so-called powder. Both ends of the body are equipped with special suction cups. The anterior sucker, surrounding the oral opening, is the sucking circle (the shroud behind). It is triangular in shape and equipped with three strong jaws, each of which has up to sixty teeth arranged in the form of a semicircular saw. The leech uses them to bite through the skin without causing much pain. Another flying bloodsucker stings much more strongly.

Among medicinal leeches in Russia, three subspecies are distinguished. The medicinal leech is brown-olive in color with six red-yellow stripes on the back, speckled with black dots, with a motley abdomen and rough rings. This form is common in Ukraine, but is also found in southern Russia. Pharmacy leech - unlike the medicinal one, it is dark green in color, with the same six stripes on the back, but without dots; the abdomen is yellowish, without spots, the rings are smooth. There are many of these leeches, also called Hungarian, in the Krasnodar Territory, Moldova, and Armenia. The eastern leech is brighter than the previous ones; narrow orange stripes covered with black triangular spots stretch along its back; the abdomen is black with green dots.

Abstract on the topic:

Plan:

1 Building
2 Food
3 Movement
4 Reproduction and life cycle
5 Hirudotherapy
6 Biology of the organism
7 Story medical use

Introduction

(lat. Hirudinea) - a subclass of annelids from the class of belt worms ( Clitellata). Most representatives live in fresh water bodies. Some species have mastered terrestrial and marine biotopes. There are about 500 species of leeches known in the world, and 62 species in Russia.

1. Structure

Body length different representatives varies from a few millimeters to tens of centimeters. The largest representative is Haementeria ghilianii(up to 45 cm).

The anterior and posterior ends of the body of leeches bear suckers. At the bottom of the anterior there is an oral opening leading to the pharynx. In proboscis leeches (order Rhynchobdelida) the pharynx is able to move outward. In jawed leeches (for example, the medicinal leech), the oral cavity is armed with three movable chitinous jaws that serve to cut through the skin.

2. Food

Leeches feed on the blood of vertebrates, mollusks, worms, etc.; there are also predator species that do not feed on blood, but swallow the prey whole (for example, mosquito larvae, earthworms). In the intestines of a leech, blood is digested slowly, and therefore, after pumping, the leech can remain without food for a long time.

3. Movement

The method of movement of leeches is interesting. There are suction cups on both ends of the worm, which it can use to attach itself to underwater objects. The leech attaches itself to them with its front end, bends into an arc, and approaches.

4. Reproduction and life cycle

Leeches are hermaphrodites. Copulation involves two individuals that simultaneously release seed material. Before laying eggs, a specialized part of the worm's integument is belt- separates the mucous cocoon containing the protein albumin. During the process of shedding from the body of the worm into the cocoon, fertilized eggs are released from the female genital opening. Subsequently, the mucous tube closes and forms a membrane that protects the embryos and subsequently young worms. Albumin acts as a food source.

5. Hirudotherapy

Hirudotherapy - treatment with leeches. A sucking leech causes local capillary bleeding, which can eliminate venous congestion, increase blood supply to the body area, in addition, substances that have an analgesic and anti-inflammatory effect enter the blood. As a result, blood microcirculation improves, the likelihood of thrombosis decreases, and swelling subsides. A reflexogenic effect is expected.

IN medical practice After use, the leech is removed by applying an alcohol swab to its head end. Getting rid of an unwanted leech is quite simple - you just need to pour a little salt on the suction cup.

It should also be noted that leeches, when attacking a person, cause hirudinosis.

6. Biology of the body

The body is elongated or oval, more or less flattened in the dorso-ventral direction, clearly divided into small rings, which, 3-5 in number, correspond to one body segment; there are numerous glands in the skin that secrete mucus; at the posterior end of the body there is usually a large sucker; often at the anterior end there is a well-developed sucker, in the center of which the mouth is placed; more often the mouth is used for suction. At the anterior end of the body there are 1-5 pairs of eyes, located in an arc or in pairs one behind the other. Powder on the dorsal side above the posterior sucker. The nervous system consists of a two-lobed suprapharyngeal ganglion, or brain, connected to it by short commissures of the subpharyngeal node (derived from several fused nodes of the abdominal chain) and the abdominal chain itself, located in the abdominal blood sinus and having about 20 nodes. The head node innervates the sensory organs and pharynx, and from each node of the abdominal chain 2 pairs of nerves depart, innervating the corresponding body segments; the lower wall of the intestine is equipped with a special longitudinal nerve that gives branches to the blind sacs of the intestine. The digestive organs begin with a mouth, armed either with three chitinous serrated plates (jawed P. - Gnathobdellidae), which serve to cut through the skin when sucking blood in animals, or capable of protruding with a proboscis (in proboscis P. - Rhynchobdellidae); Numerous openings into the oral cavity salivary glands, sometimes secreting a poisonous secretion; the pharynx, which plays the role of a pump during sucking, is followed by an extensive, highly extensible stomach, equipped with lateral sacs (up to 11 pairs), of which the posterior ones are the longest; the hindgut is thin and short. The circulatory system consists partly of real, pulsating vessels, partly of cavities - sinuses, which represent the remainder of the cavity (secondary) of the body and are connected to each other by ring canals; The blood of proboscideans is colorless, while that of jawed animals is red due to hemoglobin dissolved in the lymph. Only the river has special respiratory organs. Branchellion, shaped like leaf-like appendages on the sides of the body. The excretory organs are arranged according to the type of metanephridia, or segmental organs of annelids, and most P. have a pair of them in each of the middle segments of the body. P. are hermaphrodites: the majority of male genital organs consist of vesicles (testes), a pair in 6-12 middle segments of the body, connected on each side of the body by a common excretory duct; these ducts open outward with one opening lying on the ventral side of one of the anterior rings of the body; The female genital opening lies one segment behind the male and leads into two separate oviducts with sac-like ovaries. Two individuals copulate, each simultaneously playing the role of a female and a male. During the laying of eggs, P. secretes, through the glands located in the genital area, thick mucus, which surrounds the middle part of P.'s body in the form of a sheath; eggs are laid in this sheath, after which P. crawls out of it, and the edges of its holes come together, stick together and thus form a capsule with eggs inside, usually attached to the lower surface of the algae leaf; The embryos, leaving the facial membrane, sometimes (Clepsine) remain for some time on the underside of the mother’s body. All P. are predators, feeding on the blood of mostly warm-blooded animals or mollusks, worms, etc.; They live mainly in fresh water or in wet grass, but there are also marine forms (Pontobdella), just like terrestrial forms (in Ceylon). Hirudo medicinalis - medical P. up to 10 cm long and 2 cm wide, black-brown, black-green, with a longitudinal patterned reddish pattern on the back; the belly is light gray, with 5 pairs of eyes on the 3rd, 5th and 8th rings and strong jaws; distributed in the swamps of the South. Europe, South Russia and the Caucasus. In Mexico, Haementaria officinalis is used medicinally; another species, N. mexicana, is poisonous; In tropical Asia, Hirudo ceylonica and other related species living in humid forests and grass are common, causing painful, bleeding bites to humans and animals. Aulostomum gul o - horse P., black-green in color, with a lighter underside, has weaker mouth armament and is therefore unsuitable for therapeutic purposes; most common appearance in the north And Central Russia. Nephelis vulgaris - small P. with a thin narrow body, gray, sometimes with brown pattern on the back; equipped with 8 eyes located in an arc at the head end of the body; related to it is the original Archaeobdella Esmonti, pink color, without rear sucker; lives on the silt bottom in the Caspian and Seas of Azov. Clepsine tessel ata - Tatar P., with a broad oval body, greenish-brown color, with several rows of warts on the back and 6 pairs of triangular eyes located one after the other; lives in the Caucasus and Crimea, where it is used by the Tatars for medicinal purposes; Acanthobdella peledina, found in Lake Onega, occupies a transitional place to the order of chaetopoda Oligochaeta worms.

7. History of medical use

When writing this article, material was used from the Encyclopedic Dictionary of Brockhaus and Efron (1890-1907).

Medical leech ( Hirudo officinalis) - found in the north of Russia, especially in the south, in the Caucasus and Transcaucasia, in Poti, Lankaran. Leeches were a profitable export item in the 19th century: Greeks, Turks, Italians, etc. came to the Caucasus for them. In addition, artificial propagation leeches in special pools or parks according to the Sale system in Moscow, St. Petersburg, Pyatigorsk and Nizhny Tagil. Based on current laws catching leeches during their location - in May, June and July - is prohibited; when fishing, only those suitable for medical use should be selected, that is, at least 1 1/2 inches in length; leeches that are small or too thick should be thrown back into the water when caught. To supervise compliance with these rules, provincial medical departments are entrusted with the responsibility of verifying the stocks of leeches among barbers and other traders who trade in them. Since medicine drove leeches out of use, the leech industry has fallen completely.

With the exception of two ancient species, all leeches are divided into two large groups: some have a muscular trunk in the front part of the digestive tube, others are equipped with jaws lined with teeth. With the help of these “tools,” blood-sucking species damage the skin or mucous membranes of their victims.

A special protein substance, hirudin, is injected into the wound of the leech, which prevents blood clotting. If hirudin were not released, the damaged vessels would quickly become clogged with blood clots, which prevents blood from being sucked out.

Thanks to hirudin and other substances secreted by the salivary glands, blood can remain in a liquid state in the leech’s stomach for months without rotting.

Later it turned out that this leech attacks salmon and grayling. It lives in freshwater bodies of northern Europe and Asia, from Norway to Kolyma, and its southernmost location is Lake Onega.

Well known, widespread in almost all reservoirs of Moldova, Ukraine, the Caucasus and Central Asia(except Turkmenistan) medicinal leeches (Hirudo medicinalis). IN natural conditions they usually attack frogs and mammals that come to drink. In an aquarium, hungry medicinal leeches can attack any animal from which blood can be sucked; Naturally, the fish die after such bloodletting.

The large false horse leech (Haemopis sanguisuga), widely distributed in water bodies of Russia, Ukraine, Belarus, Moldova, and the Caucasus, is similar to the medical one. But, unlike the medical one, it is painted in gray-black tones and does not have orange-red spots. This leech is not a bloodsucker - it either swallows its prey whole or tears off pieces from it. If you set out to fatten the false horse leech, you can grow a specimen up to 40 centimeters long. A strong voracious predator eats worms (including other leeches), mollusks, larvae of aquatic insects, tadpoles, and sometimes small fish.

Representatives of the family Fish leeches (Ichthyobdellidae, or Piscicolidae) are much smaller than the species described above. It is very easy to distinguish them from other leeches: their front sucker is sharply separated from the rest of the body and usually has the shape of a disk or cup, which helps it securely attach to the fish. In most species, two pairs of eyes are located on the anterior sucker, and there are often eye-like points on the posterior one.

Piscicola lives only in water sufficiently saturated with oxygen. It is extremely rare in stagnant ponds and especially swamps.

During reproduction, the leech lays eggs enclosed in cocoons 1.5 millimeters long, which it attaches to aquatic plants and other substrates. Depending on the water temperature, after 1-3 months young leeches emerge from the cocoons and are immediately able to attack fish.

The water bodies of the Leningrad region are inhabited by the leech C. respirans, which is also very undesirable in an aquarium. Its body is relatively short (up to 40 millimeters with a width of 10), grayish-yellow in color, completely dotted with small brown pigment spots.

The body length of the snail leech rarely exceeds 20 millimeters, and the color is greenish-brown. Due to the fact that her body is translucent, it is easy to see the internal organs and the entire process of bearing offspring.

For the inquisitive naturalist, leeches can become interesting object observations. But, of course, they should be kept in a separate vessel. To prevent them from getting into the aquarium, you need to carefully examine everything that comes into it from a natural reservoir (mature leeches are visible to the naked eye) or pre-treat special techniques. If young leeches still go unnoticed and you later find them on the inhabitants of the aquarium, it is necessary to treat your pets. For fish these are short-term salt baths: 25 grams dissolved in 1 liter of water table salt and process for 10 minutes.

References

S. Sharaburin “Leeches.”

In total, about 250 species of leeches are known, the vast majority of which live in fresh water bodies.

Veils. The body is covered on the outside with cuticle. The underlying epithelium is rich in glandular mucous cells, and in ossia epithelial cells Numerous pigment cells are scattered, causing the color of leeches.

Rice. 116. Anatomy of a medicinal leech:

/ - suprapharyngeal ganglion; 2 pharynx; 3 ■-esophagus; 4 - stomach;
5 - the back will dig out the stomach; V- midgut; 7 - hindgut; N- anus; U posterior sucker; 10- ganglion of the ventral nerve cord; // - meta-pefrndpi; 12 - soaked bladder; 13 - seed sacs; 14 - vas deferens; 15 - meta-nephridnev funnels; 16
- vagina; 17 ovaries; IS epididymis; 19 - conulular organ; 20 - prostate; 21 bokonalakuna

The muscles are very developed. There are three layers in the skin-muscle bag muscle fibers, which stretch in the transverse, diagonal and longitudinal directions to the axis of the body.

The body cavity is greatly reduced and has the appearance of a system of lacunae.

Nervous system. There is a ventral nerve cord.

Sense organs. Eyes, if present, are distinguished by their primitive structure.

The integument contains sensory cells and nerve endings.

The mouth leads into the oral cavity, in which some species (for example, the medicinal leech) have

three jaws equipped with many teeth (jaw leeches), others have a proboscis with which they penetrate the integument of the victim (proboscis leeches).

The oral cavity leads to the pharynx, which plays the role of a sucking apparatus. Single-celled salivary glands open into the pharynx.

In medicinal leeches, the salivary glands secrete a special substance - hirudin, which has the property of preventing blood clotting.

Anterior section intestinal tract has several pairs of pocket-like lateral outgrowths that increase their volume, which allows for a large supply of blood, which is enough for a medicinal leech for 2-3 months. Thanks to the admixture of hirudin, the blood of leeches does not clot and remains in the blood for a long time. fresh. Digestion occurs in the endodermal part of the intestine.

Respiration in most species occurs through the integument of the body, but some species have gills.

The excretory organs are metanephridia.

Reproductive system. Leeches are hermaphrodites. Mating of medicinal leeches occurs in the spring near a reservoir in damp soil above the water level. Their large cocoons resemble acorns. They are formed by the end of June. The development of leeches in the cocoon lasts about 5 weeks. Leeches reach sexual maturity by 5 years. They live up to 20 years.

Of practical interest is the medicinal leech used to treat sick people.

External structure

Medical leech

The body of leeches is noticeably flattened in the dosoventral direction. At the anterior end there is a muscular anterior sucker, in the center, which fits the mouth opening. At the posterior end there is a second, very strongly developed posterior sucker, above which the anal opening opens on the dorsal side.

Leeches do not have any appendages or parapodia. The bristles are preserved only in a primitive species - the bristle leech. It has four pairs of setae on its five anterior segments.

Leeches very mobile, crawling and swimming animals . Having attached itself with a posterior oral sucker, the leech pulls its body forward, then attaches itself with an oral sucker, while the posterior sucker is pulled away from the substrate and the body is pulled towards the head end, bending into a loop. Then the leech is sucked again by the rear sucker, etc. In this way, leeches make “walking” movements. Leeches swim, producing wave-like movements with their whole body, during which their body bends in the dorsoventral direction.

The external ringing of leeches is false, secondary, it does not coincide with the true internal segmentation. Each real segment various leeches corresponds to 3 to 5 outer rings. The external ringing of leeches is an adaptive feature that provides body flexibility with the powerful development of the skin-muscle sac.

The body of leeches is formed by 33 segments (with the exception of the bristle leech, which has 30 segments), of which the weakly separated head lobe - prostomium - and four head segments are part of the anterior sucker. The trunk section is represented by 22 segments. The posterior sucker is formed by the fusion of the last seven segments.

Skin-muscle bag

The skin-muscular sac of leeches is formed by a single-layer epithelium, secreting a dense layered cuticle, and powerfully developed muscles. The skin of leeches is rich in glandular cells that secrete mucus and is penetrated by a network of lacunar capillaries. Under the epithelium there are numerous pigment cells, which determine the peculiar pattern of leeches.

Leeches are characterized by the presence of three continuous layers of the musculature of the skin-muscular sac, like in flatworms: the outer annular, diagonal, and the most powerful longitudinal. The dorsoventral muscles, which are not part of the skin-muscle sac, are also highly developed.

Body cavity and circulatory system

In almost all leeches, the entire space between the organs is filled with parenchyma, like in flatworms. Only in leeches does parenchyma fill the secondary body cavity, while in flatworms it fills the primary cavity.

In another order - proboscis leeches (Rhynchobdellida) - a stronger proliferation of parenchyma is observed. This leads to a partial reduction of the coelom. However, the coelomic cavity remains in the form the whole system gaps Four main coelomic lacunae run along the entire body: two on the sides, one above the intestine, surrounding the dorsal blood vessel, and another below the intestine, housing the abdominal blood vessel and the abdominal nerve cord. These lacunae communicate with each other, forming a network of smaller lacunae. Thus, proboscis leeches have both a circulatory system and a lacunar system, which is a modified coelom.

In the third order, the higher jawed leeches (Gnathobdellida), which includes the medicinal leech and many other freshwater leeches, the process of parenchyma development goes as far as in proboscis leeches. Blood vessels, lying inside coelomic lacunae in proboscis leeches, are reduced in jawed leeches. The function of the circulatory system is performed by the lacunar system, which originates from the coelom. This process of functional replacement of one organ with another, different in origin, is called substitution or organ replacement.

Excretory system

The excretory organs of leeches are represented by segmental organs of metanephridial origin. However, the number of pairs of pephrndia does not correspond to the number of segments. The medical leech has only 17 pairs of them. In connection with the transformation of the coelom into a system of lacunae, the structure of the metanephridia of leeches also changed. The metanephridial funnels open into the abdominal lacuna (coelom), but not directly into the nephridial canal. They are separated from the nephridial canal by a septum, so secreted substances penetrate from the funnel into the nephridium diffusely.

This structure of the metanephridia of leeches (separation of the funnel from the nephridial canal) is explained by the functional transformation of the lacunae into the main circulatory system, replacing the circulatory system. Metanephridia of leeches are characterized by the presence of a special expansion - the bladder.

Digestive system

The mouth is placed at the bottom of the front sucker. It leads to anterior section digestive system, lined with ectoderm and consisting of oral cavity and muscular throat. The structure of the oral cavity and pharynx is different in proboscis and jaw leeches.

In proboscis leeches, the oral cavity, growing backwards, seems to surround the pharynx in the form of a vagina. The very muscular pharynx turns into a proboscis, protruding and retracting with the help of special muscles. The proboscis can penetrate the thin coverings of various animals (for example, mollusks), and thus the leech sucks out blood.

In jawed leeches (medicinal leech, etc.), in the oral cavity there are three longitudinal muscular ridges, forming jaws, with their ridges directed towards each other. The muscle ridges are covered with chitin, jagged along the edge. With these jaws, leeches cut the skin of an animal or person. In the throat of blood-sucking jawed leeches, glands open that secrete a special substance - hirudin, which prevents blood clotting.

Next, food enters the midgut, which consists of the stomach and posterior section midgut. The stomach forms paired lateral projections, of which the last pair is usually especially developed, extending to the posterior end of the body. The stomach serves as a reservoir for long-term storage of blood. The blood that filled his pockets did not clot for weeks and months.

The posterior section of the midgut is represented by a relatively short straight tube in which final digestion and absorption of food. It passes into a short, often dilated posterior ectodermic gut, opening anus above the posterior sucker.

Nervous system and sensory organs

The nervous system of leeches consists of a paired suprapharyngeal ganglion connected by peripharyngeal connectives with the subpharyngeal ganglion mass. The latter is formed by the fusion of the first four pairs of ganglia of the ventral nerve cord. This is followed by 21 ganglia of the ventral nerve cord and a ganglionic mass (of eight pairs of ganglia) innervating the posterior sucker.

The sense organs of leeches are represented by sensitive kidneys, or goblet organs. Each such organ consists of a bundle of spindle-shaped cells located under the epithelium. The outer end of the sensory cells forms a sensory hair. Nerves from the ventral nerve cord approach the inner ends of these cells.

Some of the goblet organs perform the functions of chemical sense organs, others - tactile ones. The eyes of leeches have a similar structure to the goblet organs described above. There may be several pairs of them. The eye consists of vesicle-shaped light-sensitive cells with a large vacuole inside, to which the nerves that make up the axial part of the eye approach. The eye is surrounded by dark pigment.

Reproductive system, reproduction and development

In terms of the structure of the genital organs and method of reproduction, leeches have much in common with oligochaete ringlets. They are hermaphrodites, and their genitals are concentrated mainly in the area of the 10th and 12th body segments. Leeches have a girdle section, which, unlike oligochaetes, coincides in position with the genitals. The girdle becomes noticeable only during the breeding season.

The male reproductive apparatus consists of several pairs (4-12 or more) of testes. The medicinal leech has 9 pairs of testes located inside the seminal sacs. Short vas deferens extend from them, opening into longitudinal paired vas deferens. The latter in the area of the 10th segment form dense balls - appendages of the testes, in which sperm accumulates. Next, they pass into the ejaculatory (paired) canals, which open in the copulatory organ, which can protrude forward through the unpaired male genital opening on the 10th segment. Not everyone has a copulatory organ. In many leeches, sperm are enclosed in spermatophores. Spermatophores are either introduced into the female genital opening or stuck into the skin, and sperm penetrate the leech's body and make their way to the female genital tract.

The female reproductive apparatus consists of a pair of ovaries located in egg sacs. They pass into short and wide uteri, which connect with each other and form an unpaired oviduct, which flows into a wide vagina, which opens on the 11th segment with the female genital opening.

Fertilized eggs are laid in a cocoon secreted by the girdle. The cocoon is either attached to aquatic plants or located at the bottom of the reservoir. Some leeches lay single eggs.

Development in leeches is not direct, since larvae emerge from the eggs, remaining, however, in a cocoon. Larvae have cilia and protonephridia. The transformation of larvae occurs in the cocoon, and already formed leeches emerge from the cocoon into the water. Laying eggs in relatively strong cocoons that well protect eggs and larvae determines small quantity eggs It is measured in various leeches in units, in as a last resort in dozens.

Classification

The class of leeches is divided into three orders: 1. Bristle-bearing leeches (Acanthobdellida); 2. Proboscis (Rhynchobdellida); 3. Jawfish (Gnathobdellida).

Order Bristle-bearing leeches (Acanthobdellida)

A very primitive relict form, bearing four pairs of sharp curved setae on the five anterior segments. The anterior sucker is absent, only the posterior one is present. The parenchyma is poorly developed, there is a coelomic cavity and a circulatory system.

Order Proboscis leeches (Rhynchobdellida)

Proboscis leeches are remarkable for breeding and caring for offspring. The leech lays eggs that remain attached to the ventral side of its body. At this time, the leech is little mobile: it sits, attached with suction cups, on some plant and produces oscillatory movements body. When the eggs hatch, the leech does not change its position and the young leeches remain attached to the ventral side of the mother with their suckers, usually for several days, and then spread out and begin to lead an independent existence.

Order Jaw leeches (Gnathobdellida)

Most jawed leeches have the jaw apparatus described above in the oral cavity.

In addition to the medicinal leech (Hirudo medicinalis), common in the southern part of Russia, this order includes the ubiquitous false horse leech (Haemopis sanguisuga). This is a large, dark-colored leech, has weak jaws and is not able to bite through the skin of humans and mammals. It feeds on worms, mollusks and other invertebrates. The false-cone leech buries its cocoons in the coastal strip, above the water level.

Some jawed leeches (especially those found in southern latitudes) can be parasites of humans, for example from the genus Limnatis. One of them - L. turkestanica - is found in Central Asia. When drinking raw water from a reservoir, it can enter the human nasopharynx, where it settles and sucks blood. In addition to severe irritation, it causes bleeding. In the jungles of Sri Lanka, India, and Indonesia live land animals of the genus Haemadipsa. They hide in damp places, in grass and under leaves and attack animals and humans, causing very sensitive bites.