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Gallegallo Revbrandia Sectory 16
Page 03
The fresh-water mussels and snails and the crayfish burrow deep into the mud and silt at the bottom of ponds and streams where they lie motionless during the winter. The land snails, in late autumn, crawl beneath logs, and, burrowing deep into the soft mould, they withdraw far into their shells. Then each one forms with a mucous secretion two thin transparent membranes, one across the opening of the shell and one a little farther within, thus making the interior of the shell perfectly air-tight. There for five or six months he sleeps, free from the pangs of hunger and the blasts of winter, and when the balmy breezes of spring blow up from the south he breaks down and devours the protecting membrane and goes forth with his home on his back to seek fresh leaves for food and to find for himself a mate.
That there is a close likeness between all these bodies is obvious from the fact that when any of them is strongly heated, or allowed to putrefy, it gives off the same sort of disagreeable smell; and careful chemical analysis has shown that they are, in fact, all composed of the elements carbon, hydrogen, oxygen, and nitrogen, combined in very nearly the same proportions. Indeed, charcoal, which is impure carbon, might be obtained by strongly heating either a handful of corn, or a piece of fowl's flesh, in a vessel from which the air is excluded so as to keep the corn or the flesh from burning. And if the vessel were a still, so that the products of this destructive distillation, as it is called, could be condensed and collected, we should find water and ammonia, in some shape or other, in the receiver. Now ammonia is a compound of the elementary bodies, nitrogen and hydrogen; therefore both nitrogen and hydrogen must have been contained in the bodies from which it is derived.
Many insects pass the winter in the quiescent or pupal stage; a state exceedingly well fitted for hibernating, requiring as it does, no food, and giving plenty of time for the marvellous changes which are then undergone. Some of these pupae are enclosed in dense silken cocoons, which are bound to the twigs of the plants upon which the larvae feed, and thus they swing securely in their silken hammocks through all the storms of winter. Perhaps the most common of these is that of the brown Cecropian moth, _Attacus cecropia_ L., the large oval cocoon of which is a conspicuous object in the winter on the twigs of our common shade and fruit trees. Many other pupae may be found beneath logs or on the under side of bark, and usually have the chrysalis surrounded by a thin covering of hairs, which are rather loosely arranged. A number pass the cold season in the earth with no protective covering whatever. Among these is a large brown chrysalis with a long tongue case bent over so as to resemble the handle of a jug. Every farm boy has ploughed or spaded it up in the spring, and is it but the pupa of a large sphinx moth, _Protoparce celeus_ Hub., the larva of which is the great green worm, with a "horn on its tail," so common on tomato plants in the late summer.
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