[ 175 ] 30 



of the sides, and the loriu of the orifice, (-ombmed w ith the power the 

 insect has of moving it in every direction, results the difference we 

 see in the breadth and form of the threads, and the various thickness 

 of the same thread.* 



The silk reservoirs, following the course of the stomach, extend a<s 

 far as the last pair of membranous feet, then fold back on each side, 

 and proceed to the head, and, after two more turnings, the tubes less- 

 ening in size, they end in a series of convolutions.! Each of these 

 vessels is filled with a glutinous matter, near the time of spinning the 

 cocoon, generally of the color of the silk which the caterpillar will 

 spin. Sometimes it is of difierent colors in the same vessel; the up- 

 per part containing a yellow liquor, and the lower portion of it a pale 

 liquor. The quality of the leaves, and the constitution of the insect, 

 are the probable causes of this circumstance. While in the silk-secre- 

 tors, it assumes the appearance of a viscid gum; but the moment it is 

 exposed to the air, after being thrown out by the worm, it dries and 

 hardens into a single thread. 



The silk-caterpillar, whose life is one continued succession of 

 changes, casts ofl" its skin four times before it reaches its full growth. 

 This is a wonderful provision of nature, although, as is well known, 

 not confined to this insect, to relieve itself from the constriction it suf- 

 fers from the skin, which does not expand in proportion to the gradual 

 increase of its body. These changes are times of pain to the cater- 

 pillar, which it shows by a state of languor, and by ceasing to eat. It 

 prepares for the operation, by emjitying the intestinal tube, and by 

 throwing out, at different parts of its body, silky fibres, and attaching 

 them to the litter of its food, in order that, while it exerts itself, the 

 skin may remain fixed in the spot where it is placed. The insect is 

 now seen, at intervals, with its back elevated, or with its body stretch- 

 ed to, the utmost extent, sometimes raising its head, which is swelled 

 a-id pointed, moving from side to side, and then letting it fall. Near 

 the change, the second and third rings are seen considerably swollen. 



By these internal efforts, the old parts are stretched and distended, 

 and a slit is made on the back, generally beginning at the second or 

 third ring. The new skin ma}' now be perceived by its freshness 

 and brightness of color. The caterpillar then presses the body into 

 this opening, b}^ which means, and a continuance of swellings and 

 contractions, a rent is made from the first to the fourth ring. Then, 

 bending the forepart of its body, and drawing it backwards, it disen- 

 g;iges tlie head from its old covering, and throws it out of the slit. 

 Fiiifillv, curving the posterior rings, and drawing them towards the 

 head, the whole body escapes from its sheath. This escape is facili- 

 tated b}- a moisture, which the insect emits and diffuses over its body. 



This laborious operation is the work of an instant; and the skin, 

 when cast off, is so entire, that it might be mistaken for the larva or 

 caterpillar itself, comprising, not only the covering of the trunk, but 

 of the very skull, eyes, jaws, and legs. These changes are termed 



* Kirby and Spence's Introduction to Entomology, vol. 3, p. 125, Lond. 



+ When taken out and extended, they measure s. fuot and seven inches in lengtli. 



