52 NATURAL HISTORY. [CH. III. 



cotton, in which it is made to pass along the whole 

 circumference of the ball. This we may easily 

 imagine would be an easy task for the insect ; but if 

 a cotton-spinner were to be told that he must form 

 his ball of cotton of equal thickness throughout, but 

 that the thread must, at the same time, be arranged 

 in an irregular and more or less zigzag course, he 

 would give up his task in despair. This is, how- 

 ever, precisely what the silkworm and other cater- 

 pillars execute, as any one may observe in unwind- 

 ing the silk from the cocoon of a silkworm. 



In general, these cocoons of a firm consistence are 

 composed of an outer loose covering of silk, in the 

 middle of which the compact egg-shaped cocoon is 

 observed ; in some instances, however, the outer 

 envelope is entirely omitted, and in others it is so 

 closely spun as scarcely to differ from the cocoon 

 itself. 



Some caterpillars, in order to strengttien their 

 cocoons, moisten them with a gummy matter dif- 

 fused from the anus, after they have been completed; 

 among these the emperor moth may be mentioned : 

 In like manner the caterpillars of the lackey moth 

 {Clisiocampa neustria), the white satin moth {Leu- 

 coma salicis, &c.), emit a yellow paste-like matter, 

 which they apply by continued motions of the head 

 to the under surface of the cocoon, and this, when, 

 dry, becomes a powder which renders it opaque. In 

 some specimens which we have reared of the rare 

 lappet moth {Gastropacha quercifoUa), from caterpil- 

 lars from the fens of Cambridgeshire, we found the 

 inside of the cocoon and the body of the chrysalis 

 thickly covered with a white powder of this descrip- 

 tion. We have also observed that the chrysalis of 

 the large red-underwing moth (Caiocala nupta), is 

 covered with a powdery bloom of a bluish colour. 



Cocoons formed entirely of silk are generally the 

 work of smooth-bodied caterpillars, but many of 

 these animals are in this state very hairy, whence 



