THE NATURE OF METAMORPHOSIS. 
65 
adapted to the performance of new functions, but is equally in- 
capacitated for the continuance of some of those which it has 
previously enjoyed. It is during this period that new parts are 
developed, and the insect’s mode of life is in consequence entirely 
changed. Whilst these alterations are taking place in the organic 
structures, the functions of the organs themselves are in a great 
measure suspended, and the condition of the insect becomes that of 
the hybernating animal. Respiration and circulation are reduced 
to their minimum, and the cutaneous expenditure of the body is 
then almost inappreciable, even by the most delicate tests. Thus 
a pupa of Sphinx lignstri which in the month of August, imme- 
diately after its transformation, weighed 71*1 grains, in the month 
of April following weighed 67 '4 grains, having thus lost only 37 
grains in the long period of nearly eight months of entire absti- 
nence. The whole of this expenditure, therefore, had passed off 
by the cutaneous and respiratory surfaces. But when the changes 
in the internal structures are nearly completed, and the perfect 
insect is soon to be developed, the respiration of the pupa is 
greatly increased, and the gaseous expenditure of its body is 
augmented in the ratio of the volume of its respiration, which is 
greatest the nearer the period of perfect development. Thus, in 
the same insect in which the diminution of weight was so trifling 
during eight months’ quiescence and abstinence, it amounted in the 
succeeding fifty-one days to nearly half the original weight of the 
pupa, since the perfect insect, immediately after its appearance on 
the 24th of May, weighed only thirty-six grains. This increased 
activity of function is attended with a correspondent alteration in 
the general appearance of the pupa. 
“ In the Sphinx all the parts of the future imago become more 
and more apparent on the exterior of the pupa case, the divisions 
into head, thorax, and abdomen are more distinctly marked ; the 
eyes, antennae, and the limbs appear as if swollen, and ready to 
burst their envelope, and the pupa gives signs of increasing 
activity by frequent and vigorous contortions of its abdominal 
segments. The naked pupa, or nymph, in which, as we have 
seen, all the parts of the body are free, and encased only in a 
very delicate membrane, acquires a darker colouring and a firmer 
texture ; while the species which undergo their metamorphosis 
