78 
INTRODUCTION'. 
this the animal pushes its hinder pair of pro-legs, 
which immediately get entangled among the threads 
by the small hooks which project from a part of the 
outer edge of the foot. (Plate II. fig. 2.) The ante- 
rior part of the body is then permitted to fall down, 
and it therefore hangs in a vertical position, with the 
head lowest. Soon after, it begins to bend the head 
upwards, in such a manner that the convexity of the 
curve is formed by the back : it retains this position 
for a considerable time, then allows the head to fall 
down, and again bends itself, always taking care to 
do so in one direction. After this process has been 
continued for some time, occasionally not less than 
twenty-four hours, and in one instance mentioned by 
Reaumur, it lasted for two whole days, the skin rends 
in the back, and a portion of the chrysalis projects 
from the opening. The latter is gradually enlarged 
by the pressure and swelling of the chrysalis, which 
acts as a wedge, both in splitting the skin and in 
pushing it upwards to the tail. By alternate contrac- 
tions and expansions, the head, or lower portion of the 
chrysalis, becomes wholly disengaged; and the skin of 
the caterpillar, now dry and shrivelled, is pressed toge- 
ther into a small bundle which surrounds the tail of 
the chrysalis. This, however, is still the onlymeans of 
support, and the difficult task which yet remains for 
the chrysalis to perform, is to extricate itself from the 
skin, and suspend itself to the silken mooring, which is 
now considerably above it. In order to accomplish 
this, which seems to require an effort beyond the 
