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

1. The Fresh-water Crayfish lives in seas where it crawls about.

2. The cephalothorax of the Crayfish carries a pair of antennae.

3. The body of the Crayfish is protected by a thin chitinous exoskeleton.

4. The chitinous cover can stretch. In this way the Crayfish grows.

5. The hypodermis secretes a new layer of chitin each time the animal moults.

6. The food is digested by the gastric juice of the Crayfish.

7. The Crayfish breathes with gills, delicate feather-like frills.

8. The circulatory system of the crayfish consists of a heart and blood vessels.

9. The young cling to the abdominal appendages of the mother Crayfish.

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

1. The Crayfish feeds on … .

2. The body of the Crayfish is divided into … .

3. … carries a pair of short dovetailed appendages.

4. The abdomen ends with … … , the uropods.

5. When the animal is thrown into boiling water … , except the red one.

6. Digestion continues in … , where the food is absorbed.

7. Water … , penetrates through special openings, which … , enters the grill cavities, and moves … .

8. … , they are passed out of the body … .

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

1. Where does the Fresh-water Crayfish live?

2. Does it swim swiftly or slowly?

3. How many legs does the Crayfish have?

4. What colour is the Crayfish when alive?

5. How does the Crayfish catch its food?

6. Is the food digested by the gastric or liver juice.

7. What type of circulatory system is known as an open blood system?

8. How are wastes withdrawn from the body?

9. Do the female ovaries produce many eggs?

4. Translate a passage into Russian in written form. Text 22

ANIMALS INCLUDED IN THE CLASS ARACHNIDA

The arachnids differ from the .insects in external appearance because the body is divided into two distinct regions: a cephalothorax (combined head and thorax) and an abdomen. Besides, the arachnids have four pairs of legs, instead of three. Included in this class are the spiders, scorpions, ticks, mites, and the king crab.

Arachnids have no antennae. They breathe by means of tracheae, and, in addition, are provided with respiratory organs called book lungs. These are plate-like structures which are similar in structure and functions to gills. Most spiders are provided with glаnds called spinnerets, capable of producing a secretion which hardens on contact with the air. This secretion forms the spider's web.

Arachnids are of considerable economic importance to man. Many of them destroy large numbers of our insect pests. On the other hand, manу species of arachnids are harmful. The scorpions can inflict painful injuries through their poisonous sting, which is located on the tail of the abdomen.

Mites and ticks are parasites of man and domestic animals.

Garden Spider.

When walking through a wood in late summer, you may seе many spiders' cobwebs. The instinct enabling the spider to spin cobwebs is its most remarcable feature. The threads it spins are very fine, but it can put then together with the help of the comblike little claws on its hind legs to form a thick, nonadhesive line.

Catch a fly and throw it into one of them. At once a big spider with a light-coloured cross on its back will leap upon the fly from its place of concealment. If the Garden Spider is big, it is a female; if small - a male.

It is very interesting to watch the spider deal with its prey. It first entagles it in a thin web and then pierces the body with its upper jaws. Each jaw carries a sharp flexible fang which can be drawn in and out.

Through a small opening at the tip of the fang, poison is injected into the fly's body. The fly becomes paralysed and dies.

As soon as the fly is dead, the spider quietly returns to its shelter.

Structure.

The body consists of a cephalothorax and an abdomen. Four pairs of segmented legs and two pairs of jaws are attached to the underside of the cephalothorox. One of the jaws has already been mentioned. The second pair is like two short legs on the sides of which are feelers. These are called padipalps and act as organs of touch. Grouped along the front edge of the cephalothorax are four pairs of simple eyes.

The abdomen, the most conspicuous part of the spider's body, has no external segmentation. On its posterior end is a battery of little projections, the teat-like spinnerets. The spinnerets secrete a fluid which is produced in the glands and which hardens on the exposure to air to become delicate thread from which cobwebs and the cocoons that enclose the spider's eggs are constructed.

Some spiders use the web as a means of moving to a new home: a newly-hatched spider spins out a long thread, which floats in the wind until it becomes entangled in an adjacent tree. This provides a line along which to walk.

Considerable distances can be covered in this way helping spiders to spread fast throughout a locality.

Food.

When a spider bites a fly it injects into it аn effective poison together with digestive juices. The juices dissolve the fly's inner organs reducing them to a semi-fluid mass. After a time, the spider returns to its prey and sucks out the contents, leaving nothing but the empty, chitinous covering.

Reproduction.

In autumn the female spins a tiny golden-yellow ball-like silk cocoon, in which it lays several scores of eggs. It then dies.

If you catch а large female in autumn and keep it in a test tube for some time, you will be able to watch the сосооn-and egg-laying process by уоurself.

Having survived the winter, the eggs hatch into young spiderlings. The spiderlings have never seen a web; much less have they had a chance to learn how to construct one, and yet they behave at once like adult, experienced spiders, "spinning" and "waving" with the greatest skill. This shows convincingly that the instinctive behaviour of animals is hereditary.

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