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Биология Class Amphibia
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Text 1

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Температура тела амфибий зависит от температуры и влажности окружающей среды; они отличаются ограниченными возможностями распространения, передвижения и ориентации на суше. Примитивность амфибий как наземных животных особенно ярко выражена в том, что их яйца лишены оболочек, защищающих их от высыхания, и, как правило, не могут развиваться вне воды. В связи с этим у земноводных развивается личинка, обитающая в воде. Развитие протекает с превращением (метаморфоз), в результате которого водная личинка превращается в животное, обитающее на суше. Земноводные — самый малочисленный класс позвоночных, включающий лишь около 2100 современных видов, представленных тремя отрядами: хвостатых, безногих и бесхвостых.

A

An amphibian - any member of the class Amphibia, vertebrates distinguished by their ability to exploit both aquatic and terrestrial habitats. The name, derived from the Greek amphibios meaning “living a double life,” reflects this dual life strategy. Despite this distinction, however, some species are permanent land dwellers, while other species have a completely aquatic mode of existence.

B

Members of the three living orders of amphibians, Anura ( frogs and toads), Caudata (salamanders and newts), and Apoda ( caecilians), differ in their structural appearance. Frogs and toads are tailless, somewhat squat amphibians with long, powerful hind limbs modified for leaping. Salamanders and newts have tails and two pairs of limbs of roughly the same size and have less-specialized structures than the other two orders. Caecilians are limbless, wormlike, and highly adapted for a burrowing existence.

C

Most amphibians have a biphasic life cycle involving aquatic eggs and larvae that metamorphose into terrestrial adults. They deposit large numbers of eggs in water; clutches may exceed 5,000 eggs in the tiger salamander (Ambystoma tigrinum) and 45,000 eggs in large bullfrogs (Rana catesbeiana). Egg size and water temperature influence the length of time required by embryos to develop in the egg before hatching;

D

Adult amphibians consume a wide variety of foods. Earthworms are the main diet of burrowing caecilians, anurans feed primarily on insects and other arthropods, and large salamanders and some large anurans eat small vertebrates, including birds and mammals. Most anurans and salamanders locate prey by sight, although some use their sense of smell.

E

Toad any squat, rough-skinned, tailless amphibian of the order Anura, and especially a member of the family Bufonidae. The true toads (Bufo), with more than 300 species, are found worldwide except in Australasia, Madagascar, polar regions, and Polynesia.

True toads, of which the American toad and the European toad are representative, are stout-bodied with short legs that limit them to the characteristic walking or hopping gait. Their size ranges from about 2 to 25 cm. The thick, dry, often warty skin on the back is generally brown. Poison-secreting glands are located on the back and in the warts but are most concentrated in two prominent raised areas behind the eyes, the parotid glands.

True toads are mainly terrestrial and nocturnal. They frequently remain in fairly small areas, feeding on whatever insects or small animals they can catch with their sticky tongues. Most remain in their burrows in winter and during drought. They breed in water and may migrate 1.5 km or more to a suitable breeding pond. The eggs (600 to over 30,000, depending on species) are laid (spawn) in two long jelly tubes. The tadpoles hatch in a few days and transform into adults in one to three months.

F

The poison, which is secreted or ejected when the toad is disturbed, irritates the eyes and mucous membranes of many, though not all, predators. The poisons of the Colorado River toad and the giant toad affect animals as large as dogs, in some instances causing temporary paralysis or even death. The Chinese have long used dried toad poison to treat various ailments. Contrary to popular belief, toads do not cause warts.

G

In many parts of the world, freezing temperatures are common. Aquatic animals in these climates must be able to survive when temperatures fall below freezing. It is well documented that wood frogs actually freeze solid in winter! The lenses of their eyes turn white when they freeze. But when spring arrives, these same frogs thaw out and hop away to get on with their lives! How do they avoid the damage that freezing causes for most creatures? Their cells concentrate sugars, which lowers the freezing point for the cytoplasm and prevents freezing.


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