LEPIDOPTEEA. 151 



to fix itself. After having covered it thus with a kind of thin 

 cobweb, it adds different 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 suspends itself. By 

 alternate movements of contraction and elongation of 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 fall in a vertical position. 



It remains hanging thus, often for twenty-four hours, during 

 which time it is occupied in a difficult task, that of splitting its 



Figs. 104, 105. Pupae of the small Tortoise-shell Butterfly freeing themselves from 

 the Caterpillar skin. 



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 

 pupa. 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 opening is sufficient to allow of the chrysalis drawing 

 out the fore part of its body from the envelope, which it im- 

 mediately does. To set itself entirely free, the chrysalis lengthens 

 and shortens itself alternately (Fig. 105). Each time that it 



