272 INSECT ARCHITECTURE. 



is never deceived in adjusting the dimensions of tlie 

 [united] apertures, or in calculating the proper thickness of 

 the thread, but invariably makes the strength of it propor- 

 tionable to the weight of her body. 



" It would be a very curious thing to know how the gum 

 which composes the silk is separated and drawn off from 

 the other juices that nourish the animal. It must be 

 accomplished like the secretions formed by glands in the 

 human body. I am therefore persuaded that the gum-bags 

 of the silk- worm are furnished with a set of minute glands, 

 which, being impregnated with gum, afford a free passage 

 to all the juices of the mulberry-leaf corresponding with 

 this glutinous matter, while they exclude every fluid of a 

 different quality."* When confined in an open glass vessel, 

 the goat-moth caterpillar will effect its escape by construct- 

 ing a curious silken ladder, as represented by Eoesel. 



Caterpillars, as they increase in size, cast their skins 

 as lobsters do their shells, and emerge into renewed ac- 

 tivity under an enlarged covering. Previous to this 

 change, when the skin begins to gird and pinch them, 

 they may be obsei-ved to become languid, and indifferent 

 to their food, and at length they cease to eat, and await 

 the sloughing of their skin. It is now that the faculty 

 of spinning silk seems to be of great advantage to them ; 

 for being rendered inactive and helpless by the tighten- 

 ing of the old skin around their expanding body, they 

 might be swept away by the first puff of wind, and 

 made prey of by ground beetles or other carnivorous 

 prowlers. To guard against such accidents, as soon as 

 they feel that they can swallow no more food, from being 

 half choked by the old skin, they take care to secure 

 themselves from danger by moorings of silk spun upon 

 the leaf or the branch where they may be reposing. 

 The caterpillar of the white satin-moth {Leucoma salicis, 

 Stephens) in this way draws together with silk one or 

 two leaves, similar to the leaf-rollers (Tortricidce), though 

 it always feeds openly without any covering. The cater- 

 pillar of the puss-moth again, which, in its third skin, is 

 * Spectacle de la Nature, vol. i. 



