SILKWORM. The 'silkworm' of commerce is the caterpillar of ROM bys ato•i, a moth of the family Bombyeiche, a group commonly known as the family of silkworm moths. The caterpillars of all of the species of this group have the silk glands largely developed, and many of them spin large quantities of silk in making their cocoons. The Bombycithe have a very short and rudi mentary proboscis, live for a very short time in their perfect state., and take little o• no food; the body is thick and hairy; the wings are large and broad ; the antenna are pectinated. The caterpillars feed on the leaves and other tender parts of trees o• other plants; the chrysa lids are inclosed in a cocoon of silk. The com mon silkworm is a native of either the northern provinces of China or of Bengal. The perfect insect is about an inch in length. the female rather larger than the male, the color whitish, with a broad pale brown bar across the upper wings. The females generally (lie very soon after they have laid their eggs, and the males do not survive much longer. The eggs are numerous. bluish in color, about the size of a pin's head, not attached together, but fastened to the sur face on which they are laid by a gummy sub stance, which, when dry, becomes silky. They are laid about the end of June. and are hatched about the middle of the follo?%ing April, or at the time when the leaves of the mulberry unfold.
The caterpillar is at first small, not more than a quarter of an inch in length, but rapidly increases in size, till, when full grown, it is nearly three inches long. It is usually of a yel lowish gray color, but slane varieties are much darker. The skin is changed four times during the growth of the caterpillar. Before each change of skin it becomes lethargic, and ceases to eat, whereas at other times it is very vora cious. When the skin is ready to be cast off,
it bursts at the fore part, and the caterpillar then, by continually writhing its body, without moving from the spot. thrusts it backward ; hut silkworms frequently die during the change of skin. A very rapid increase of size takes place while the new skin is still soft. The natural food of the silkworm is the leaf of the white mulberry, hut it will also feed on the leaves of some other plants, as black mulberry and let tuce, and in the United States it is frequently fed on the Osage orange. When so fed, however, it produces silk of inferior quality. The silk producing organs are two large glands (seric teria) containing a viscid substance, which ex tend along a great part of the body. and termi nate in two spinnerets in the mouth. These. glands become very large when the change to the chrysalis or pupa state is about to take place.
When about to spin a cocoon, the silkworm ceases to eat, and first produces the rough fibre which forms the outer part of the cocoon, and then the more closely disposed and valuable fibre of its interior. In this process the position of the hinder part of the body is little changed, but the head is moved from one point to another; and the cocoon when finished is much shorter than the body. Each fibre of silk, when examined by a microscope, is seen to he double, being equally derived from the two silk-producing or gans of the caterpillar. A single fibre ranges from SOO to 1000 yards in length. The time of the silkworm's life in the caterpillar state is about four weeks. About three days are occupied in the spinning of the cocoon; after which about two or three weeks elapse in the chrysalis stage be fore the perfect insect comes forth.