60 TRANSFORMATIONS OF INSECTS. 
extended and shortened, as if the insect were in the act of laborious 
respiration. This generally takes place at short intervals during 
the two hours immediately preceding the change, and increases 
in frequency as that period approaches. When that period has 
arrived, the skin bursts along the back part of the third segment, 
or mesothorax, and is extended along the second and fourth, while 
the coverings of the head separate into three pieces. The insect 
then exerts itself to the utmost to extend the fissure along the 
segments of the abdomen, and in the meantime, pressing its body 
through the opening, gradually withdraws its antenne and legs, 
while the skin, by successive contortions of the abdomen, is 
slipped backwards, and forced towards the extremity of the body, 
just as a person would slip off his glove or his stocking. The 
efforts of the insect to get entirely rid of it are then very great ; 
it twists itself in every direction, in order to burst the skin, and 
when it has exerted itself in this manner for some time, twirls 
itself swiftly, first in one direction and then in the opposite, until 
at last the skin is broken through and falls to the ground, or 
is forced to some “distance. _The “new ‘pupa’! then hanes for 
a few seconds at rest, but its change is not yet completed. The 
legs and antennez, which when withdrawn from the old skin were 
disposed along the under-surface of the body, are as yet separate, 
and do not adhere together as they do a short time afterwards. 
The wings are also separate, and very small. In a few seconds 
the pupa makes several slow but powerful respiratory efforts, 
during which the abdominal segments become more contracted 
along their under-surface. The wings are then much enlarged and 
are extended along the lower surface and sides of the body ; more- 
over, a very transparent fluid, which facilitated the slipping off 
of the skin, is now diffused among the limbs, and when the pupa 
becomes quiet, dries and unites the whole into one compact 
covering. Exactly the same thing occurs in the changes of the 
Sphinx. The limbs at first are all separate, each one being 
enclosed in its distinct sheath, but within a very short period after 
the change they become agglutinated together by the fluid diffused 
between them, and form the solid exterior of the pupa case. 
“The three thoracic legs can be distinguished from the mem- 
branous legs of the hinder segments. Within the body, and 
