200 STATES OF INSECTS. (Larva.) 
mean, and size of insects in this state. As to s7ze, larvee 
differ as much as insects in their perfect state: these last, 
however, never grow after their exclusion from the pupa, 
while larvee increase in bulk in a proportion, and often 
with a rapidity, almost without a parallel in the other 
tribes of animals. ‘Thus Lyonnet found, that the cater- 
pillar of the great goat-moth (Cossus ligniperda), after 
having attained its full growth is at least 72,000 times 
heavier than when it was first excluded from the egg*; 
and of course had increased in size in the same proportion. 
Connected with the size of larvee, is the mode in which 
their accretion takes place. This, with respect to the 
more solid parts, as the head, legs, &c., is not, as in other 
animals, by gradual and imperceptible degrees, but sud- 
denly and at stated intervals. Between the assumption 
of a new skin and the deposition of an old one, no in- 
crease of size takes place in these parts, while the rest of 
the body grows and extends itself, till, becoming too big 
for these solid parts, nature restores the equilibrium be- 
tween them by a fresh moult®, in which the augmenta- 
tion of bulk, especially in these parts, is so great, that we 
can scarcely credit the possibility of its being cased in so 
small an envelope. Malpighi declares, that the head of 
a silk-worm that has recently cast its skin is four times 
larger than before the change‘. It is very probable, 
also, that when the outer skin becomes rigid, it confines 
the body of the larva within a smaller compass than it 
would expand to if unconfined, so that, when this com- 
pression is removed, the soft and elastic new integu- 
@ Lyonnet 11. 
b N. Dict. d Hist. Nat. vi, 290. 
© De Bombycibus, 68. 
