LEPIDOPTERA. 



147 



fy (Vanessa urticix) undergoing their 

 metamorphoses. 



layers of threads on a small portion of this surface, in such a manner 

 that the upper one is always smaller than that upon which it is laid. 

 In this manner a small hillock 

 of silk is formed, the tissue of 

 which is not at all compact. 

 It resembles an assemblage 

 of loose or badly interwoven 

 threads. The membranous 

 feet of the caterpillar are armed 

 with hooks of different lengths, 

 with the aid of which it sus- 

 pends itself. By alternately 

 contracting and elongating its 

 body, it pushes its hindermost 

 legs against the hillock of silk, 

 presses against it the hooks of 

 its feet, so as to get them better 



entangled, and lets its body Figs. 102, 103. Caterpillars of the small Tortoise-shell 



fall in a vertical position. 



It remains hanging thus, 

 often for twenty-four hours, 

 during which time it is oc- 

 cupied in a difficult task, that 

 of splitting its skin. In order 

 to effect this, it incessantly 

 curves and recurves its body 

 (Fig. 102), until at last a split 

 appears on the skin of the 

 back, and through this split 

 emerges a part of the body of 

 the chrysalis. This acts as a 

 wedge, and little by little the 

 split widens from the head to 

 the last of the true legs, and 

 beyond them. Then the open- 

 ing is sufficient to allow of 

 the chrysalis drawing out its 

 anterior portion from the en- 

 velope, which it immediately does. To set itself entirely free, the 

 chrysalis lengthens and shortens itself alternately (Fig. 105). Each 

 time that it shortens itself, and when it consequently distends the 

 part of its body which is outside the old skin, that parts acts against 



K 2 



Figs. 104, 105. -Chrysalides of the small Tortoise- 

 shell Butterfly freeing themselves from the 

 Caterpillar skin. 



