1. Write down whether the following statements are true or false. Give extensive answers.

1. All of the annelids are free-living found in both fresh and salt water.

2. Earthworms live in the soil as they do not need oxygen.

3. Earthworms cannot see but they can distinguish between darkness and light.

4. The senses of touch taste and smell are not important for Earthworms.

5. Anterior and posterior ends and dorsal and ventral sides of Earthworms are similar.

6. The worm’s skin is thick and covers three layers of muscular cells.

7. Earthworms make the soil friable and deepen the fertile layer of the soil.

8. The channels in the soil burrowed by worms prevent the penetration of water and air into the soil.

2. Complete the sentences using the text and translate them into Russian.

1. The annelids include … worms.

2. Oxygen enters the earthworm’s body through … .

3. The worm’s skin is … .

4. The senses of … help the earthworm to find food easily.

5. Animals having … are said to have developed bilateral symmetry.

6. Earthworms are useful animals which contribute to … .

7. Earthworms make the soil … .

3. Answer the following questions on the text in written form.

1. What does the name “annelid” mean?

2. What ring of worms do the annelids include?

3. In what places do the annelids live?

4. What is the habitat of Earthworms?

5. Why are earthworms often called rain-worms?

6. What is the structure of the Earthworm’s body?

7. What animals are said to have bilateral symmetry?

8. In what way do Earthworms contribute to soil formation?

4. Translate a passage into Russian in written form. Text 12 the structure of earthworm

Tissues

The Earthworm is a multicellular animal. The cells, of which its tissues are formed - the epithelium (cover tissue) and the muscular and nervous tissues - are similar in structure and function. The epithelium covers the body protecting it from injury.

The muscular tissue consists of tall column-shaped cells whose basic feature is the ability to contract (contractibility). The contractions of the muscular cells give rise to movements.

The two characteristic features of the nervous issue are excitability and the ability to pass on stimulation, i.e. conduction.

Body Cavity

Together with the muscles the skin forms a dermomuscular cylinder. Inside the cylinder is the body cavity with the intestines.

The Earthworm's body cavity is subdivided into many sections by thin transverse partitions which coincide with the grooves between the segments. The segmentation is both external and internal.

Digestive System

The upper side of the mouth of the Earthworm is covered by a lip. The worm uses this to seize pieces of decaying leave. The material then is passed into the muscular pharynx and on into the oesophagus.

Past the oesophagus the tube widens into a crop, where food is held and moistened before it moves on to the muscular-walled gizzard here it is ground up into a pulpy mass and passed into the intestine.

The cells of the intestine walls excrete digestive juice the action of which dissolves the food. The dissolved food is absorbed by the walls of the intestine and passes into the blood vessels. The undigested remains are propelled by circular contractions of the intestine towards the anus and excreted. There digestion ends.

Respiration

Oxygen enters the blood through the skin. The blood of the Earthworm is red. The haemoglobin, which is dissolved in the blood, plays an important part in transferring oxygen throughout the body. The haemoglobin assimilates oxygen easily and as easily gives it away to the cells.

By means of the circulation of the blood oxygen is fed to all the organs in exchange for carbon dioxide which is excreted through the skin.

Circulatory System

Two blood vessels run along the body like thin red threads, one above the intestine known as the dorsal vessel, the other under the intestine called the ventral vessel. In the anterior end both vessels meet and are connected by two large circular vessels, the pseudo-hearts, so named because of their ability to contract and thereby keep blood circulating.

Blood flows from the dorsal into the ventral vessel. The vessel divides into finer branches which reach all the cells. From the blood the cells receive the nutrient matter, without which they cannot live, and oxygen, which is necessary for respiration. In return, the cells excrete harmful fluids and carbon dioxide into the blood.

Flowing through the thinnest epithelial vessels the blood absorbs oxygen and gives off carbon dioxide. The excreted fluids pass from the blood stream into the body cavity.

Excretion

The excretory organs are nephridia. There are two nephridia in almost all the segments. Each nephridium looks like a tube. It begins in the body cavity with a fan-shaped funnel and has a narrow exterior opening. The edge of the fan-shaped funnel is bordered with cilia. Moving continually, the cilia draw the excreted matter from the body cavity into the nephridia, and pass it out.

Reproduction

Each Earthworm has two kinds of germ glands: female - ovaries, in which the ova (eggs) develop, and male - testis in which spermatozoa are stored. The Earthworms are bisexual, like the Hydras.

Fertilized eggs develop inside a hard cocoon which forms around the Earthworm's body from fluid thrown out from the girdle in the anterior end of the worm. Eggs and spermatozoa are discharged into the cocoon and the eggs are fertilized. The worm then crawls out of the cocoon. Both ends of the cocoon contract to form a capsule looking like a lemon. The capsule remains in the soil protecting the eggs from dryness and other unfavourable conditions.

Organs

The organs of digestion are arranged in the following order: mouth, pharynx, oesophagus, crop, muscular-walled gizzard, intestine and anus. This order provides for a gradual transformation of food and its digestion, i.e., the formation of matter which can pass through the walls of the intestine into the blood and can be absorbed by all cells in the worm's body. All the organs participating in food digestion are united into the digestive system.

The circulatory system is composed of blood vessels. It is issued to circulate blood which carries nutrient matter and dissolved gases.

The nephridia make up the excretory system, which helps to remove water and toxic matter formed in the organism of the worm. The excreted fluid can be compared to urine. More highly-developed animals also have a respiratory system, which is however absent in Earthworms.

The ventral nerve cord, the nerve belt and the nerves are the component parts of the nervous system. Finally, there is also the reproductive system.

Conclusion

The annelids are considered more highly developed animals than those which we have previously studied, for the following reasons:

1. The body is segmented and the internal organs are segmentally arranged.

2. Of all the phyla we have discussed thus far, the annelid worms are the first to have a well-developed body cavity, so that the body structure consists of a tube within a tube.

3. They have a more highly developed brain and nervous system.

4. There is a higher degree of specialization and division of labour than is found in the lower phyla. Therefore, it can be presumed that they appeared on the Earth later than the coelenterates.

Despite considerable structural variations, worms have many common features: an elongated body, no legs and no hard skeleton.

Depending on their specific structural features, worms are divided into several groups. Earthworms belong to the Segmented Worms (Annelids). Ascaris, Lung Flukes, Pin-worms and Sugar-beet Eelworms are called Roundworms (Nematodes). Pork Tapeworms, Liver Flukes, Echinococcus and Brainworms are known as Flatworms (Platyhelminthes).

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