56 TRANSFORMATIONS OF INSECTS. 
some other larve. Lyonet found that the larva of Cossus lig- 
niperda, which remains about three years in that state, in- 
creased to the amount of 72,000 times its first weight. This 
amazing increase is occasioned chiefly by a prodigious accumu- 
lation of fat, which exists in a greater quantity in this than in 
most other larvae. We have ourselves removed forty-two grains of 
fat from one specimen, which was more than one-fourth of the 
whole weight of the insect. The occasion for this prodigious 
accumulation is chiefly to supply the insect during its continuance 
in the pupa state, while the muscular structure of the limbs and 
other parts of the body are in the course of development, and 
also to serve, perhaps, as an immediate source of nutriment to the 
insect at the period of its assuming the perfect state, and more 
particularly during the rapid development of its generative func- 
tions ; since, when these have become perfected, the quantity that 
remains is very inconsiderable. But all larve do not increase in 
these amazing proportions, although their actual increase may be 
more rapid. Those in which the proportion of increase is the 
greatest are usually those which remain longest in the pupa state, 
as in the species first noticed. Thus Redi observed in the maggots 
of the common flesh flies a rate of increase amounting to about 
200 times the original weight in twenty-four hours; but the 
proportion of increase in these larvae does not at all approach that 
of the Sphinx and Cossus. From observations made on the larva 
of one of the wild bees, Axthophora retusa, we believe that this is 
also the case with the ymenoptera. The weight of the egg of 
this insect is about the 150th part of a grain, and the average 
weight of a full-grown larva is six and eight-tenths grains, so 
that its increase is about 1,020 times its original weight, which, 
compared with that of the Sphinx of medium size, is but as 
one to nine and three quarters, and to a Sphinx of maximum 
size, only as one to a little more than eleven. 
“The changes of skin which a larva undergoes before it enters 
the pupa state are more or less frequent in different species. In 
the generality of lepidopterous insects it occurs about five times, 
but in one of the Tiger-moths, Avctia caja, according to’ Messrs. 
Kirby and Spence, ten times. A few hours before the change 
is to take place the larva ceases to eat, and remains motionless, 
