6 



and on each side of it is placed a silk gland (fig. 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 annually in the spring. Simple contact 

 with the air causes the new-born insect imme- 

 diately to acquire a volume 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 

 paler 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 body raised up, for a 

 period of time varying according to tempera- 

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

 during which time the body undergoes extraor- 

 dinary modifications. The skin is entirely 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 facilitate this difficult change a liquid is secreted between the old 

 skin and the one forming beneath it. 



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

 length according to temperature, frequency of feeding, race, and the 

 robustness of the worm. The following is about the average: 

 First age, from birth to first molt, five to six days. 

 Second age, from first to second molt, four days. 

 Third age, from second to third molt, four to five days. 

 Fourth age, from third to fourth molt, five to seven days. 

 Fifth age, from fourth molt to maturity, seven to twelve days- 



165 



Fig. 2.— Silk glands in a ma- 

 ture worm: p, portion of 

 glands wtdch secrete the 

 silky matter; s, reservoir; 

 c, conducting canal; /, spin- 

 neret; g, accessory glands 

 (redrawn from Verson and 

 Quajat). 



