LETTERS ON ENTOMOLOGY. 30 
mur's description is nearly precise. The first 
operation of the caterpillar, when near its change, 
is to spin a curious little ball, or mound, of silk 
on the spot it has fixed on, composed of numer- 
ous little loops crossing each other. This being 
done, it prepares to suspend itself by its two 
hinder feet, which, like the others, are half sur- 
rounded by two rows of hooks of different sizes. 
The moment it presses these feet against the ball 
of silk, they are entangled among the loops. 
When they are safely fastened, it puts itself in a 
vertical position with the head downwards. It 
then bends its body upwards, making the back 
convex, and sometimes remains thus half an hour 
or more; this, which is often repeated, is to 
crack the skin on the back, that the chrysalis 
may come forth. The operation generally takes 
at least twenty-four hours, and sometimes two 
days ; but as soon as the least crack is made, it 
is quickly enlarged by the chrysalis, which swells 
its body with an undulating motion till the 
skin is split far enough to discover the upper 
part, which is so much larger than the envelope 
it quits, that it is surprising how it could be 
contained in it ; but it is the nature of the chry- 
salis to grow shorter and wider almost at the 
moment of its change. When the upper part is 
