It is now about one and a half or two inches in length, and devours its food most voraciously, increasing rapidly in size during ten days. When the worms are fed a slight hissing noise is heard similar to that of green wood burning. According to some writers this noise proceeds from the action of the jaws, but others attribute it solely to the action of the feet, which are continually moving until the worms have fastened to their food, when the noise ceases. In a large nursery of silkworms this noise sounds like a soft shower of rain. [Illustration: SILKWORM ON MULBERRY-LEAF. ] When the caterpillar has attained its full growth, it is a very different creature from the little black worm which first issued from the egg, being from two and a half to three inches in length, and its body consisting of twelve membranous rings, which contract and elongate as the animal moves. It is furnished with sixteen legs, in pairs: three pairs in front, under the first three rings, are covered with a shelly or scaly substance; the other five pairs, called holders, are furnished with little hooks, which assist the insect in climbing. The head is covered with a scaly substance similar to the covering of the fore legs. The mandibles are of great strength, and indented like the teeth of a saw. Beneath the jaw are two small openings, through which the insect draws its silken lines. The substance of which the silk is composed is a fine yellow transparent gum, secreted in two slender vessels, “which are wound, as it were, on two spindles in the stomach; if unfolded, these vessels would be about ten inches in length.” The insect breathes by means of eighteen holes or spiracles, distributed along the body, nine on each side. On each side of the head, near the mouth, are seven small eyes; the two specks higher up on the head, which are generally mistaken for eyes, are only parts of the skull. [Illustration: FULL GROWN SILKWORM. ] When the silkworm is ready to spin, it gets upon the leaves without eating them, rears its head as if in search of something, or crawls to the edges of the tray and moves slowly along; its rings draw in, and its greenish colour changes to a deep golden hue; its skin becomes wrinkled about the neck, and its body feels like soft dough, and on taking it in the hand, and looking through it, the whole body has assumed the transparency of a ripe yellow plum. When this is observed, the owner of the insects puts each singly into a little cone of white paper, which he pins to the wall or elsewhere, so that the creature may be undisturbed at its work. But in the nurseries abroad little bushes are set up on the wicker shelves, and the insects mount them and form their cocoons among the twigs.