ments of munducation are strong and efficient; the digestive organs greatly developed, and the skin periodically thrown off to remove any impediment to the distention of the body. The consumption of food is necessarily great, in some cases exceeding that of any other animals, regard being had to their respective size. In fact, many of the kinds which consume the foliage of plants eat with little intermission; and, in some instances, they continue to feed both by night and day. The growth of the larvæ of flesh-flies (Sarcophaga) is unusually rapid, some of them having been found to become 200 times heavier in twenty-four hours. When it has attained its full growth, the caterpillar of the goat moth is sometimes 72,000 times heavier than when newly hatched. The experiments of Count Dandalo on the silk-worm, make it appear that when just hatched, this caterpillar is a line in length, and a hundred weigh about a grain; after the first moulting, the length of each is four lines, and a hundred weigh fifteen grains; after second moulting, length 6 lines, weight 94 grains; after third moulting, length 12, weight 400; after fourth moulting, length 20, weight 1628; after fifth moulting, the length of each is upwards of three inches, and a hundred weigh about 9500 grains.
The number of these moultings or changes of skin varies greatly in different insects, but it is always alike in the same species. The intervening periods likewise vary, being dependent on the length of life allotted to the larvæ. In the silk worm, as has just been seen, the moultings are five, and all these occur
