8 



THE CULTUKE OF THE MULBERRY SILKWORM. 



The head is a small mass covered with a hard scale, and is provided 

 with jaws that move laterally, like the wings of a folding- door. The 

 alimentary canal extends throughout the entire length of the body, 

 and on each side of it is placed a silk gland (tig. 2). These consist of 

 two whitish or amber-colored cords, which after innumerable curves 

 unite in the spinneret in the region of the mouth. There are also two 

 glands, whose excretory canal opens in the spinneret, and covers the 

 silk as it comes out with an impermeable varnish rendering it insoluble 

 in acids and alkalies. This varnish is about a 

 fifth of the weight of the thread. 



Hatchings usually occur annuall}^ in the 

 spring. Simple contact with the air causes the 

 new-born insect immediately to acquire a vol- 

 ume larger than it had in the egg, and it quickly 

 begins to gnaw the under surface and edges of 

 the mulberry leaf. It eats day and night at 

 all hours, except when asleep, and in about 

 thirty days grows 14,000 times larger than it 

 was at birth. 



As the silkworm grows larger it becomes 

 ))aler in color, because its dark chestnut brown 

 hairs are scattered over a larger surface, thus 

 showing more of the true color of the skin. 



About five days from its birth the vitality 

 of the larva decreases, and it eats scantily or 

 not at all, and becomes thin and whitish in color. 

 Then it moves around unquietly, and finding a 

 convenient place attaches itself to it, holding on 

 by its false feet. It thus remains motionless, 

 with the front part of its bod}^ raised up, for a 

 period of time var^ang according to tempera- 

 ture, and takes its first so-called "sleep," or 

 molt, during which time the body undergoes 

 extraordinary modifications. The skin is en- 

 tirely shed, and all the tissues that can not keep 

 up with the rapid growth of the insect are changed. 



The scale which covers the snout is the first part of the case to fall, 

 and a new case appears under the former one. The worm then pushes 

 itself forward through its first ring, sets at liberty the legs of the 

 thorax, and by a wriggling movement comes out of its old sheath. 



To aid the insect in this difiicult change a liquid is secreted between 

 the old skin and the one forming beneath it, which facilitates the 

 separation. 



The life of the larva is usually divided into five ages, varying in 



Fig. 2.— Silk glands in a ma- 

 ture worm: p, portion of 

 glands which secrete the 

 silky matter; s, reservoir; 

 c, conducting canal ; /, spin- 

 neret; g, accessory glands 

 (redrawn from Verson and 

 Quajat). 



