Зоология на английском. Обязательный материал для чтения на занятиях и дома. Сологуб Л.И. - 20 стр.

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5. The mixing of voided earth with the litter had led to disappearance of the mat

as a discrete layer*

VI. On the basis of the article prove the importance of the earthworms for soil

formation.

VII. Make up a model of its information and sum it up.

Text 12

I. Read the text and state what information it carries.

PHYSIOLOGICAL BASIS OF THE ODOR HYPOTHESIS

Students of fish behavior have long observed that fish have an extremely

acute sense of smell. It is well known that shark and tuna are drawn to a vessel

by the odor of bait in the water. Karl von Prisch was among the first to

demonstrate scientifically the effect of an odor upon the behavior of fishes.

During his studies he noticed that when a bird dropped in injured fish into the

water, the school of fishes from which it had been seized quickly dispersed and

later avoided the area. This observation led von Frisch (1941) to prove in the

laboratory that fish can be alarmed by extremely dilute emanations from injured

fish skin. Папу other workers have demonstrated the importance of the fish

olfactory sense in locating food and recognizing other fish. Odors may also warn

fishes away from poisons. In fact we (Easier and Wisby, 1950) found that fishes

can sense low concentrations of certain industrial pollutions and their behavior

can be utilized as a qualitative biological assay of pollution. In contrast, the

common chemical sense and the mechanism that permits temperature gradient

discrimination are imprecise and less sensitive when compared with the

olfactory system.

The olfactory organs of fishes have evolved in a great variety of forms. In

the teleosts or bony fishes, of which the salmon is a representative, the nose pits

have two separate openings. Water enters the anterior opening as the fish swine

(cilia sometimes assisting the intake), passes over nasal receptors, and flows out

through a second opening, which in some species, may be opened and closed

rhythmically by the fish's gill ventilation. Any odorous substances in the water

stimulate the nasal receptors chemically, perhaps by an effect on еnzyme

reactions, and the resulting nerve impulses are relayed to the central nervous

system by the olfactory nerve.