The seed scale of a female pine cone is how many ovules there are. Pine development cycle. The structure of a female pine cone

The hydra's body looks like an oblong sac, the walls of which consist of two layers of cells - ectoderm And endoderm.

Between them lies a thin gelatinous non-cellular layer - mesoglea, serving as a support.

The ectoderm forms the covering of the animal’s body and consists of several types of cells: epithelial-muscular, intermediate And stinging.

The most numerous of them are epithelial-muscular.

Ectoderm

epithelial muscle cell

Due to muscle fibers, lying at the base of each cell, the body of the hydra can contract, lengthen and bend.

Between the epithelial-muscle cells there are groups of small, round cells with large nuclei and a small amount of cytoplasm, called intermediate.

When the hydra's body is damaged, they begin to grow and divide rapidly. They can transform into other types of cells in the hydra body, except for epithelial-muscular ones.

The ectoderm contains stinging cells, serving for attack and defense. They are mainly located on the tentacles of the hydra. Each stinging cell contains an oval capsule in which the stinging filament is coiled.

Structure of a stinging cell with a coiled stinging thread

If prey or an enemy touches a sensitive hair located outside the stinging cell, in response to irritation the stinging thread is ejected and pierces the body of the victim.

Structure of a stinging cell with discarded stinging thread

Through the thread channel, a substance that can paralyze the victim enters the victim’s body.

There are several types of stinging cells. The threads of some pierce the skin of animals and introduce poison into their bodies. The threads of others are wrapped around the prey. The threads of the third are very sticky and stick to the victim. Usually the hydra “shoots” several stinging cells. After the shot, the stinging cell dies. New stinging cells are formed from intermediate.

The structure of the inner layer of cells

Endoderm lines the entire intestinal cavity from the inside. It includes digestive-muscular And glandular cells.

Endoderm

Digestive system

There are more digestive muscle cells than others. Muscle fibers they are capable of reduction. When they shorten, the hydra's body becomes thinner. Complex movements (movement by “tumbling”) occur due to contractions of muscle fibers of ectoderm and endoderm cells.

Each of the digestive muscle cells of the endoderm has 1-3 flagella. Hesitating flagella create a current of water, which drives food particles towards the cells. Digestive muscle cells of the endoderm are capable of forming pseudopods, capture and digest small food particles in the digestive vacuoles.

The structure of the digestive muscle cell

Glandular cells in the endoderm secrete digestive juice into the intestinal cavity, which liquefies and partially digests food.

The structure of the glandular cell

Prey is captured by the tentacles using stinging cells, the venom of which quickly paralyzes small victims. By coordinated movements of the tentacles, the prey is brought to the mouth, and then, with the help of body contractions, the hydra is “put on” the victim. Digestion begins in the intestinal cavity ( cavity digestion), ends inside the digestive vacuoles of epithelial-muscular endoderm cells ( intracellular digestion). Nutrients are distributed throughout the hydra's body.

When the digestive cavity contains remnants of the prey that cannot be digested, and waste from cellular metabolism, it contracts and empties.

Breath

Hydra breathes oxygen dissolved in water. She has no respiratory organs, and she absorbs oxygen over the entire surface of her body.

Circulatory system

Absent.

Selection

The release of carbon dioxide and other unnecessary substances formed during life processes is carried out from the cells of the outer layer directly into the water, and from the cells of the inner layer into the intestinal cavity, then out.

Nervous system

Below the skin-muscle cells are star-shaped cells. These are nerve cells (1). They connect with each other and form a nerve network (2).

Nervous system and irritability of the hydra

If you touch the hydra (2), then excitation (electrical impulses) occurs in the nerve cells, which instantly spreads throughout the entire nervous network (3) and causes contraction of the skin-muscle cells and the entire body of the hydra shortens (4). The response of the hydra body to such irritation is unconditioned reflex.

Sex cells

With the approach of cold weather in the fall, germ cells are formed from intermediate cells in the ectoderm of the hydra.

There are two types of germ cells: eggs, or female germ cells, and sperm, or male germ cells.

The eggs are located closer to the base of the hydra, sperm develop in tubercles located closer to the mouth.

egg cell Hydra is similar to an amoeba. It is equipped with pseudopods and grows rapidly, absorbing neighboring intermediate cells.

The structure of the hydra egg cell

The structure of the hydra sperm

Sperm By appearance resemble flagellated protozoa. They leave the hydra's body and swim using a long flagellum.

Fertilization. Reproduction

The sperm swims up to the hydra with the egg cell and penetrates inside it, and the nuclei of both sex cells merge. After this, the pseudopods are retracted, the cell is rounded, a thick shell is released on its surface - an egg is formed. When the hydra dies and is destroyed, the egg remains alive and falls to the bottom. With the onset of warm weather, the living cell located inside the protective shell begins to divide, the resulting cells are arranged in two layers. From them a small hydra develops, which comes out through a break in the egg shell. Thus, the multicellular animal hydra at the beginning of its life consists of only one cell - an egg. This suggests that the ancestors of Hydra were single-celled animals.

Asexual reproduction of hydra

Under favorable conditions, hydra reproduces asexually. A bud forms on the animal’s body (usually in the lower third of the body), it grows, then tentacles form and a mouth breaks through. The young hydra buds from the mother's body (in this case, the mother and daughter polyps are attached by tentacles to the substrate and pull in different directions) and leads an independent lifestyle. In autumn, hydra begins to reproduce sexually. On the body, in the ectoderm, gonads are laid - sex glands, and in them, germ cells develop from intermediate cells. When hydra gonads form, a medusoid nodule is formed. This suggests that the hydra gonads are highly simplified sporifers, the last stage in the series of transformation of the lost medusoid generation into an organ. Most species of hydra are dioecious; hermaphroditism is less common. Hydra eggs grow rapidly by phagocytosis of surrounding cells. Mature eggs reach a diameter of 0.5-1 mm. Fertilization occurs in the body of the hydra: through a special hole in the gonad, the sperm penetrates the egg and merges with it. The zygote undergoes complete uniform fragmentation, as a result of which a coeloblastula is formed. Then, as a result of mixed delamination (a combination of immigration and delamination), gastrulation occurs. A dense protective shell (embryotheca) with spine-like outgrowths is formed around the embryo. At the gastrula stage, the embryos enter suspended animation. Adult hydras die, and the embryos sink to the bottom and overwinter. In the spring, development continues, in the parenchyma of the endoderm, an intestinal cavity is formed by divergence of cells, then the rudiments of tentacles are formed, and a young hydra emerges from under the shell. Thus, unlike most marine hydroids, hydra does not have free-swimming larvae and its development is direct.

Regeneration

Hydra has a very high ability to regenerate. When cut crosswise into several parts, each part restores the “head” and “leg”, maintaining the original polarity - the mouth and tentacles develop on the side that was closer to the oral end of the body, and the stalk and sole develop on the aboral side of the fragment. The whole organism can be restored from individual small pieces of the body (less than 1/100 of the volume), from pieces of tentacles, and also from a suspension of cells. At the same time, the regeneration process itself is not accompanied by increased cell division and represents typical example morphallaxis.

Movement

In a calm state, the tentacles extend several centimeters. The animal slowly moves them from side to side, lying in wait for prey. If necessary, the hydra can move slowly.

"Walking" mode of transportation

"Walking" method of movement of the hydra

Having curved its body (1) and attached its tentacles to the surface of an object (substrate), the hydra pulls the sole (2) to the front end of the body. Then the walking movement of the hydra is repeated (3,4).

"Tumbling" mode of movement

"Tumbling" method of movement of the hydra

In another case, it seems to tumble over its head, alternately attaching itself to objects with its tentacles and its sole (1-5).

The common hydra lives in freshwater bodies, attaches one side of its body to aquatic plants and underwater objects, and leads sedentary lifestyle life, feeds on small arthropods (daphnia, cyclops, etc.). Hydra is a typical representative of coelenterates and has characteristic features of their structure.

External structure of the hydra

The hydra's body size is about 1 cm, excluding the length of the tentacles. The body has cylindrical shape. On one side there is mouth opening surrounded by tentacles. On the other side - sole, they attach the animal to objects.

The number of tentacles can vary (from 4 to 12).

Hydra has a single life form polyp(i.e., it does not form colonies, since during asexual reproduction the daughter individuals are completely separated from the mother; hydra also does not form jellyfish). Asexual reproduction occurs budding. At the same time, a new small hydra grows in the lower half of the hydra’s body.

Hydra is capable of changing its body shape within certain limits. It can bend, bend, shorten and lengthen, and extend its tentacles.

Internal structure of the hydra

Like all coelenterates, in terms of the internal structure of the body, the hydra is a two-layer sac that forms a closed structure (there is only a mouth opening) intestinal cavity. The outer layer of cells is called ectoderm, internal - endoderm. Between them there is a gelatinous substance mesoglea, mainly performing a supporting function. The ectoderm and endoderm contain several types of cells.

Mostly in the ectoderm epithelial muscle cells. At the base of these cells (closer to the mesoglea) there are muscle fibers, the contraction and relaxation of which ensures the movement of the hydra.

Hydra has several varieties stinging cells. Most of them are on the tentacles, where they are located in groups (batteries). The stinging cell contains a capsule with a coiled thread. On the surface of the cell, a sensitive hair “looks” out. When the hydra's victims swim by and touch the hairs, a stinging thread shoots out of the cage. In some stinging cells, the threads pierce the arthropod's cover, in others they inject poison inside, in others they stick to the victim.

Among the ectoderm cells, Hydra has nerve cells. Each cell has many processes. Connecting with their help, nerve cells form the hydra nervous system. Such a nervous system is called diffuse. Signals from one cell are transmitted across the network to others. Some processes of nerve cells contact epithelial muscle cells and cause them to contract when necessary.

Hydras have intermediate cells. From them other types of cells are formed, except epithelial-muscular and digestive-muscular. All these cells provide the hydra with a high ability to regenerate, that is, restore lost parts of the body.

In the body of the hydra in the fall they are formed germ cells. Either sperm or eggs develop in the tubercles on her body.

The endoderm consists of digestive muscle and glandular cells.

U digestive muscle cell on the side facing the mesoglea there is a muscle fiber, like epithelial muscle cells. On the other side, facing the intestinal cavity, the cell has flagella (like euglena) and forms pseudopods (like amoeba). The digestive cell scoops up food particles with flagella and captures them with pseudopods. After this, a digestive vacuole is formed inside the cell. The nutrients obtained after digestion are used not only by the cell itself, but are also transported to other types of cells through special tubules.

Glandular cells secrete a digestive secretion into the intestinal cavity, which ensures the breakdown of prey and its partial digestion. In coelenterates, cavity and intracellular digestion are combined.

The body shape of the hydra is tubular. The mouth opening of these animals is covered with tentacles. Hydras live in water, and with their stinging tentacles they kill and bring prey to their mouths.

   Type - Coelenterates
   Class - Hydroid
   Genus/Species - Hydra vulgaris, H.oligactis, etc.

   Basic data:
DIMENSIONS
Length: 6-15 mm.

REPRODUCTION
Vegetative: has a budding character. A bud appears on the mother’s body, from which a daughter gradually develops.
Sexual: Most species of hydra are dioecious. The gonads contain cells from which eggs develop. Sperm cells develop in the testis.

LIFESTYLE
Habits: live in fresh and brackish waters.
Food: plankton, fish fry, ciliates.
Lifespan: no data.

RELATED SPECIES
More than 9,000 species belong to the type of coelenterates, some of them (15-20) live only in fresh water Oh.

   Freshwater hydras are one of the smallest predators. Despite this, they are able to provide themselves with food. Hydras have a tubular body shape. Using their soles, they attach themselves to underwater plants or rocks and move their tentacles in search of prey. Green hydras contain photosynthetic algae.

FOOD

   Hydra is a predatory animal that lives in water. It feeds on small organisms living in water, for example, ciliates, oligochaete worms, planktonic crustaceans, water fleas, insects and their larvae, and fish fry. A hydra that hunts attaches itself to an aquatic plant, branch or leaf and hangs on it. Her tentacles are very wide open. They constantly make circular searching movements. If one of them touches the victim, others rush towards it. Hydra paralyzes prey with stinging cell venom. The hydra uses its tentacles to pull its paralyzed prey towards its mouth. She swallows small animals whole. If the prey is larger than the hydra, the predator opens its mouth wide and the walls of its body stretch. If such prey is so large that it does not fit into the gastric cavity, then the hydra swallows only part of it and, to the extent of digestion, pushes the victim deeper and deeper.

LIFESTYLE

   Hydras live alone. However, in places that are especially rich in food, several hydras hunt at once. This happens because the water current brings a lot of food into the specific place. Hydras of the Nuiga genus prefer fresh water. These animals were discovered by the researcher who invented the microscope, A. Leeuwenhoek (1632-1723). Another scientist, G. Tremblay, discovered that hydras easily restore lost body parts. An inconspicuous tubular body, crowned with tentacles that grow around the mouth opening, and a sole at the end of the body are the main features of the hydra's appearance. The gastric cavity of this animal is continuous. The tentacles are hollow. The body walls consist of two layers of cells. There are glandular cells located in the middle part of the hydra's body. Various types very similar to each other. They differ mainly in color (and, as a result, different colors indicate some structural feature). Bright green hydras have symbiotic algae living in their bodies. Hydras react to light and swim towards it. These animals are sedentary. They spend most of their lives in an attached state, waiting for prey. With the sole, like a suction cup, hydras are firmly attached to plants.

REPRODUCTION

   Hydras reproduce in two ways - sexual and vegetative. Vegetative propagation is represented by budding. Under suitable external conditions, several buds develop on the hydra’s body. At the very beginning, the bud looks like a small mound, later miniature tentacles appear at its outer end. The tentacles grow and stinging cells appear on them. The lower part of the body of the daughter individual becomes thinner, the hydra's mouth opens, the young individual branches off and begins an independent life. These animals reproduce by budding in the warm season. With the onset of autumn, hydras begin sexual reproduction. Sex cells are formed in the gonads. The gonad cracks and an egg emerges. Around the same time, sperm are formed in the testes of other hydras. They also leave the gonad and swim in the water. One of them fertilizes the egg. An embryo develops in the egg. Protected by a double shell, it overwinters at the bottom. In the spring, a fully formed hydra emerges from the egg.
  

DID YOU KNOW THAT...

• Hydra does not age, since every cell in its body is renewed after a few weeks. This animal lives only in the warm season. With the beginning of winter, all adult hydras die. Only their eggs, protected by a strong double shell - the embryotheca, can survive the winter.
• Hydras easily restore their lost limbs. The scientist G. Tremblay (1710-1784), as a result of his numerous experiments, obtained a seven-headed polyp, from which severed heads grew back. He looked like a mythical creature - the Lernaean Hydra, defeated by a hero ancient Greece- Hercules.
• During constant movements in the water, the hydra performs quite original acrobatic tricks.

  

CHARACTERISTIC FEATURES OF HYDRA

   Tentacles: the mouth opening is surrounded by a corolla with 5-12 tentacles with stinging cells. With their help, the animal paralyzes its prey and pulls it into its mouth. A hydra that hunts attaches itself to a hard surface and, spreading its tentacles widely, makes circular searching movements with them.
   Body: body shape is tubular. At the anterior end is a mouth opening surrounded by tentacles. The aboral pore is located in the middle of the sole. The hydra wall consists of two layers of cells. Digestive processes take place in the midsection of the body.
   Mouth opening: covered with a corolla of tentacles. With its tentacles, the hydra pulls the animal into its mouth and swallows it.
   Leg: The rear end of the hydra is narrowed - this is a leg that has a sole at the end.
   Gonads: are formed in the ectoderm and have the appearance of tubercles. Sex cells accumulate in them.
   Dome: length about 13 mm. This is for self-defense. The hydra rises and forms a dense dome.
   Bud: The vegetative propagation of hydra has the nature of budding. Several buds may appear on the body at the same time. The buds are growing quickly.

PLACES OF ACCOMMODATION
Freshwater hydras live in fresh and brackish waters. They inhabit rivers, lakes, swamps and other bodies of water. The most common species are the common and brown hydra.
SAVE
Each species of a genus living in a certain territory. These days they are not in danger of extinction.

Who among us has not read books about the colorful world of coral polyps in the shallow waters of tropical seas! But about the fact that a relative of these polyps lives in our overgrown stagnant reservoirs - hydra(Hydra) (though not very close), hardly anyone knows. And he is remarkable.

It is very difficult to find hydras in a body of water. They sit on plants, stones, pieces of wood in the water, but if you take any of these objects out of the water, you will see nothing but an inconspicuous slimy lump. You need to do it differently: collect plants from a densely overgrown pond, put them in a jar or aquarium with water and let everything calm down. After this, examine the contents through the glass. This is where you will see them. These are small creatures in the shape of a short, narrow cylinder, which is attached at the base to an underwater object and carries several flexible thread-like tentacles at the free end. There are hydras with variable thickness of the axial part of the body: it is thicker, and closer to the base it turns into a narrow stalk. This stalked or brown hydra (Hydra oligactis).

Hydra is extremely simple. Its body is a bag, at the free end of which a mouth opening opens, surrounded by tentacles. This bag consists of two layers of cells - outer and inner. The first brings the body into contact with the external environment, the second assimilates the caught food. Food (primarily very small animals floating in the water column, such as crustaceans) is caught by the tentacles.

To catch crustaceans and other small animals, the hydra, like all representatives of cnidarians, has a powerful weapon - batteries of stinging cells. There are especially many of them on the tentacles, which is why they sometimes look knotty. Inside each such cell lies a large oval capsule with a sensitive hair sticking out, and in the capsule itself there is a thread twisted into a spiral, which is a thin tube.

So, hydra is on the hunt. Daphnia swims near its tentacles with characteristic jumps. Suddenly she touched the hydra's tentacle, and something stopped her. And no matter how long you wait, the daphnia will no longer budge. Let us now select the victim from the hydra and examine it through a microscope. We will see many different stinging cells on the body of daphnia. Some of them, having pierced, injected poison into it, which is why it stopped moving, others wrapped themselves in several rings around the legs and bristles of the daphnia, and, finally, others simply stuck to the body - with them the hydra attracts prey to itself. The paralyzed victim is attached to the tentacle by microscopic “harpoons” (usually there are many of them and they different types). The tentacle bends, brings the prey to its mouth, and the hydra slowly swallows it. The body swells (the prey is often wider), and the process of digestion begins, carried out primarily inside the cells lining the intestinal cavity. Undigested food remains are expelled through the mouth.

On some hydras you can notice a kind of branching. Not far from the base, a second, small polyp emerges - this is a kidney. She will separate when she grows up and live an independent life. Hydras move slowly. They separate from the substrate on which they sit, turn their tentacles towards it and thus crawl or “walk” very slowly.

Hydra can reproduce both by budding and sexually. In the upper part of the hydra’s body there are small tubercles where sperm are formed, and in the lower part, closer to the point of attachment, there are large protrusions where eggs are formed.

Some hydras, such as the green hydra ( Hydra viridissima), have a bright green color, depending on the presence of unicellular algae in their body. Algae supply the hydra tissues with oxygen and some organic substances, and the hydra, in turn, provides them with nitrogen and phosphorus compounds necessary for plants.

One of the most remarkable abilities of hydras is the ability to rebuild their body from small pieces. The famous Danish writer Hans Scherfig, in his short book “The Pond,” written with extraordinary love for everything living on Earth, described the discovery of this ability of the hydra this way: “The twenty-fifth of September 1740 is a significant day in the history of zoology. On this day, the Swiss Abraham Tremblay cut a freshwater hydra polyp into two parts. Both parts continued to live after the operation. From one piece, called Tremblay's "head", a new body grew, and from the other, a new "head" arose fourteen days after the experiment." Other experiments told by Scherfig in this book are also noteworthy: “The hydra is small, only two and a half centimeters. Such a small creature was divided into one hundred pieces - and from each piece a new hydra arose. They split it in half and prevented the halves from merging - they got two interconnected with each other other animals. They dissected the hydra into bundles - a bunch-shaped colony of hydras was formed... When several hydras were cut and allowed separate parts grow together, the result was completely monsters: organisms with two heads, with several heads... And these monstrous, ugly forms continued to live..." Just like the mythical Lernaean hydra - a multi-headed snake with which Hercules fought and whose name this freshwater creature received polyp.

Hydra, although an inconspicuous and even inconspicuous inhabitant of our fresh waters, plays a noticeable role in reservoirs - in the thicket zone it significantly affects the number of small animals. In addition, the hydra gives a general idea of ​​the structure and lifestyle of primitive and ancient group animals - cnidarians.

Literature: Crayfish, mollusks. Ya. I. Starobogatov. Nature of the Leningrad region, 1988

In lakes, rivers or ponds with clean, clear water, attached animals that look like frayed twine are often found on the roots of duckweed, stems and leaves of other aquatic plants. This Hydras. Externally, Hydras look like small translucent brownish or greenish stems with a corolla tentacles at the free end of the body. Hydra is a freshwater polyp (“polyp” means “multipede”).

Hydras are radially symmetrical animals. Their body is in the form of a bag measuring from 1 to 3 cm (and the body usually does not exceed 5-7 mm in length, but the tentacles can stretch several centimeters). At one end of the body there is sole, used for attachment to underwater objects, on the opposite - oral hole, surrounded by long tentacles(5-12 tentacles). In our reservoirs, Hydra can be found from the beginning of June to the end of September.

Lifestyle. Hydras – predatory animals. They catch prey with the help of tentacles, on which they are located in huge numbers stinging cells. When you touch the tentacles, long threads containing strong toxins. Killed animals are pulled by tentacles to the mouth opening and swallowed. Hydra swallows small animals whole. If the victim is somewhat larger than the Hydra itself, it can also swallow it. At the same time, the predator’s mouth opens wide, and the walls of the body are greatly stretched. If the prey does not fit entirely into the gastric cavity, the Hydra swallows only one end of it, pushing the victim deeper and deeper as it is digested. Undigested food remains are also removed through the mouth. Hydras prefer daphnia (water fleas), but they can also eat other crustaceans, ciliates, various insect larvae and even small tadpoles and fry. A moderate daily diet is one daphnia.

Hydras usually lead a motionless lifestyle, but can crawl from place to place, sliding on their soles or tumbling over their heads. They always move in the direction of the light. When irritated, animals are able to shrink into a ball, which may also help them with bowel movements.

Body structure. The Hydra's body consists of two layers of cells. These are the so-called two-layer animals. The outer layer of cells is called ectoderm, and the inner layer is endoderm (endoderm). Between the ectoderm and endoderm there is a layer of structureless mass - mesoglea. The mesoglea in sea jellyfish makes up up to 80% of the body weight, while in Hydra the mesoglea is not large and is called supporting record.

Genus Hydra - Hydra

Inside the Hydra's body is gastric cavity (intestinal cavity), opening outward with one single hole ( oral hole).

IN endoderm are located epithelial-muscle and glandular cells. These cells line the intestinal cavity. The main function of the endoderm is digestive. Epithelial-muscle cells, with the help of flagella facing the intestinal cavity, push food particles, and with the help of pseudopods they capture them and pull them inside. Food is digested in these cells. Glandular cells produce enzymes that break down proteins. The digestive juice of these cells enters the intestinal cavity, where digestion processes also occur. Thus, Hydra has two types of digestion: intracavitary(extracellular), characteristic of other multicellular animals, and intracellular(characteristic of unicellular and lower multicellular organisms).

In the ectoderm Hydra has epithelial-muscular, nerve, stinging and intermediate cells. Epithelial-muscle (cover) cells cover the body of the Hydra. Each of them has a long process elongated parallel to the surface of the body, in the cytoplasm of which there are developed contractile fiber. The combination of such processes forms a layer of muscular formations. When the fibers of all epithelial muscle cells contract, the Hydra's body contracts. If the fibers contract on only one side of the body, then the Hydra bends in that direction. Thanks to the work of muscle fibers, Hydra can slowly move from place to place, alternately “stepping” with its sole and tentacles.

Stinging or nettle cells There are especially many tentacles in the ectoderm. Inside these cells is capsule with a poisonous liquid and a coiled tubular thread. On the surface of stinging cells there is sensitive hair. These cells serve as Hydra's weapons of attack and defense. When prey or an enemy touches a sensitive hair, the stinging capsule instantly throws the thread out. The poisonous liquid, entering the thread, and then through the thread into the animal’s body, paralyzes or kills it. Stinging cells die after a single use and are replaced by new ones formed by intermediate cells.

Intermediate cells small, round, with large nuclei and a small amount of cytoplasm. When the Hydra's body is damaged, they begin to rapidly grow and divide. Epithelial-muscular, nerve, germ and other cells can be formed from intermediate cells.

Nerve cells scattered under the integumentary epithelial-muscular cells, and they are stellate in shape. The processes of nerve cells communicate with each other, forming a nerve plexus that thickens around the mouth and on the sole.

Genus Hydra - Hydra

This type of nervous system is called diffuse- the most primitive in the animal world. Some of the nerve processes approach the skin-muscle cells. The processes are capable of perceiving various irritations (light, heat, mechanical influences), as a result of which excitation develops in the nerve cells, which is transmitted through them to all parts of the body and animal and causes an appropriate response.

Thus, Hydra and other Coelenterates have real fabrics, although little differentiated - ectoderm and endoderm. The nervous system appears.

Hydra does not have special respiratory organs. Oxygen dissolved in water penetrates the hydra through the entire surface of the body. Hydra also has no excretory organs. The end products of metabolism are excreted through the ectoderm. Sense organs are not developed. The sense of touch is carried out over the entire surface of the body, the tentacles (sensitive hairs) are especially sensitive, throwing out stinging threads that kill or paralyze prey.

Reproduction. How does Hydra reproduce? asexual, so sexual way. During the summer it reproduces asexually - budding. In the middle part of the Hydra's body there is a budding belt on which tubercles are formed ( kidneys). The bud grows, a mouth and tentacles form at its apex, after which the bud thins out at the base, separates from the body of the mother and begins to live independently. This resembles the development of a plant shoot from a bud - hence the name of this method of propagation.

In autumn, with the approach of cold weather, sex cells are formed from intermediate cells in the ectoderm of Hydra - spermatozoa And eggs. Stalked Hydras dioecious, and their fertilization cross. The egg cells are located closer to the base of the Hydra and are similar to an amoeba, and the sperm are similar to flagellated protozoa and develop in tubercles located closer to the mouth opening. The sperm has a long flagellum, with which it swims in water and reaches the eggs, and then merges with them. Fertilization occurs inside the body of the mother. The fertilized egg begins to divide, becomes covered with a dense double shell, sinks to the bottom and overwinters there. In late autumn, Hydras die. And in the spring, a new generation develops from overwintered eggs.

Regeneration. When the body is damaged, cells located near the wound begin to grow and divide, and the wound quickly closes (heals). This process is called regeneration. Regeneration occurs in many animals, and humans also have it. But not a single animal can compare with Hydra in this matter. Perhaps the hydra got its name precisely for this property (see the second labor of Hercules).

Lernaean Hydra (Second Labor of Hercules)

After the first feat, King Eurystheus sent Hercules to kill the Lernaean hydra. It was a monster with the body of a snake and nine heads of a dragon. The hydra lived in a swamp near the city of Lerna and, crawling out of its lair, destroyed entire herds and devastated the entire surrounding area. The fight with the nine-headed hydra was dangerous because one of its heads was immortal. Hercules set off on a journey to Lerna with his friend Iolaus. Arriving at a swamp near the city of Lerna, Hercules left Iolaus with his chariot in a nearby grove, and he himself went to look for the hydra. He found her in a cave surrounded by a swamp. Having heated his arrows red-hot, Hercules began to shoot them one after another into the hydra. The arrows of Hercules enraged the Hydra. She crawled out, wriggling a body covered with shiny scales, from the darkness of the cave, rose menacingly on her huge tail and was about to rush at the hero, but the son of Zeus stepped on her torso with his foot and pressed her to the ground. The hydra wrapped its tail around the legs of Hercules and tried to knock him down. Like an unshakable rock, stood The hero, with swings of his heavy club, knocked down the heads of the hydra one after another. The club whistled in the air like a whirlwind; The hydra's heads flew off, but the hydra was still alive. Then Hercules noticed that in the hydra, in place of each knocked-down head, two new ones grew. Help for the hydra also appeared. A monstrous cancer crawled out of the swamp and dug its claws into Hercules’ leg. Then the hero called Iolaus for help. Iolaus killed the monstrous cancer, set fire to part of the nearby grove and, with burning tree trunks, burned the hydra's necks, from which Hercules knocked off the heads with his club. The hydra has stopped growing new heads. She resisted the son of Zeus weaker and weaker. Finally, the immortal head flew off the hydra. The monstrous hydra was defeated and fell dead to the ground. The victor Hercules buried her immortal head deeply and piled a huge rock on it so that it could not come out into the light again.

If we talk about the real Hydra, then its ability to regenerate is even more incredible! A new animal can grow from 1/200 of a Hydra; in fact, a whole organism is restored from the pulp. Therefore, Hydra regeneration is often called an additional method of reproduction.

Meaning. Hydras are a favorite subject for studying regeneration processes. In nature, Hydra is an element of biological diversity. In the structure of the ecosystem, Hydra, as a predatory animal, acts as a second-order consumer. No animal simply wants to feed on Hydra itself.

Questions for self-control.

Name the systematic position of Hydra.

Where does Hydra live?

What body structure does Hydra have?

How does Hydra eat?

How does Hydra excrete waste products?

How does Hydra reproduce?

What is the significance of Hydra in nature?

Genus Hydra - Hydra

Rice. The structure of Hydra.

A - longitudinal section (1 - tentacles, 2 - ectoderm, 3 - endoderm, 4 - gastric cavity, 5 - mouth, 6 - testis, 7 - ovary and developing zygote).

B - cross-section (1 - ectoderm, 2 - endoderm, 3 - gastric cavity, 4, 5 - stinging cells, 6 - nerve cell, 7 - glandular cell, 8 - supporting plate).

B - nervous system. G - epithelial muscle cell. D - stinging cells (1 - in a dormant state, 2 - with a discarded thread; the nuclei are painted black).

Genus Hydra - Hydra

Rice. Reproduction of Hydra.

From left to right: Hydra with male gonads, Hydra with female gonads, Hydra during budding.

Rice. Hydra movement.

Hydras move, attaching to the substrate either with the sole or with a mouth cone with tentacles.