MODES OF EMERGING FROM PUP.^.. 323 



thin as writing-paper. The head of this pupa being 

 obtuse, it cannot of course cut through this wooden 

 covering, thin as it is, but can only push against it 

 till it burst it open, which we have more than once 

 seen it actually do.* It is enabled to exert consi- 

 derable force in this process, by means of the beauti- 

 fully-serrated structure of its rings, resembling in this 

 respect the caterpillars of cossus and other wood- 

 borers. 



Pupae of Cossus, a, and ^geria, b, showing the serratures of 

 their rings. 



Lyonnet justly remarks that in the cossus there 

 ; are sharp points upon the head for the purpose of 

 ' making the first breach, the rest of the body acting 

 ; as a wedge to tear open the cocoon. Professor Peck 

 I has given a very interesting account of similar pro- 

 i ceedings in the case of the locust-moth {Cossus Ro- 

 binifp. Peck). " In the silk-moth," he says, " and 

 all others which I have had an opportunity to ob- 

 serve, the chrysalis bursts in the cocoon ; and the fluid 

 which surrounded the new insect in it escaping at the 

 same time, so weakens or dissolves the fibre and 

 texture of the silk,t that the moth is able to extri- 

 cate itself, leaving the chrysalis behind it ; but this is 

 not the manner in the locust-moth. After remaining 

 till all its parts are fully grown, and it is ready to 

 quit its prison, a certain quantity of exercise is ne- 

 cessary to break the ligaments which attach the moth 



* JR. 



f See some observations on this doctrine, "Insect Architec- 

 ture," pages 31(5, 317, and 195. 



