CH. XVII.] CHRYSALIS. 287 



back by elevating- the head ; and in this position it 

 will remain for more than half an hour. This 

 movement is frequently repeated ; and at each suc- 

 ceeding repetition of it, the body of the caterpillar 

 acquires a greater degree of convexity. A strain is 

 thus occasioned in the skin of the back, which soon 

 produces a rent in that part. This process a work 

 of at least twenty- four hours and great labour 



causes the skin to break at last, and a portion of the 

 chrysalis becomes visible through the rent. White 

 confined by the skin of the caterpillar, the chrysalis 

 is long and narrow ; but as soon as a fissure has 

 been made in this outward covering, it begins to 

 contract, and its anterior portion swells out so much, 

 that the rent is thereby rapidly enlarged. As soon 

 as the fissure has been rendered sufficiently large to 

 permit a portion of the chrysalis to protrude, the 

 mode of action is changed. By various contortions 

 and movements of the body, the skin is ttirust to- 

 wards the tail, much in the same manner as we push 

 down a stocking towards the foot. The length of 

 the skin becomes thus compressed 'nto a multitude 

 of folds. 



