STATES OF INSECTS. (Larva.) 193 
insect in its pupa state. Above this are placed several 
others, which successively become external integuments. 
These changes or casting of the skin in larvee, analogous, 
as before observed, to that of serpents, are familiar to 
every breeder of silk-worms, in which four such changes 
occur: the first at the end of about ¢welve days from its 
birth, and the three next each at the end of half that 
time from the moulting which preceded it. With some 
exceptions *, similar changes of the skin take place in all 
larvae, not however in the same number and at the same 
periods. Most indeed undergo this operation only three 
or four times; but there are some that moult oftener, 
from five up to eight (Luprepia villica), nine (EH. Do- 
minula), or even ten times; for so often, M. Cuvier in- 
forms us, the caterpillar of the tiger-moth (£. Caja) casts 
its exuviee. It has been observed that the caterpillars of 
the day-flying Lepidoptera (Papilio, L.) usually change 
only three times, while those of the night-flying ones 
(Phalena L.) change four’. The periods that intervene 
between each change depend upon the length of the in- 
sect’s existence in the larva state. In those which live 
only a few weeks or months, they are from eight to 
twenty days; while in those that live more than a year, 
as the cockchafer, &c. they are probably proportionably 
longer: though we know very little with regard to the 
moult of any insects besides the Lepzdoptera. 
A day or two previously to each change of its skin, 
4 Those Diptera whose metamorphosis is coarctate (Vor. I. p.67), 
bees, the female Cocci, &c. do not cast their skin in the larva state. 
Reaum. iv. 364. N. Dict. d’ Hist. Nat. xx. 365. 
> N. Dict. d'Hist. Nat. vi. 289. xx. 372. Cuvier Anat. Comp. ii. 
548. M. Cuvier (Ibid. 547.) asserts, that most Papiliones and Boni- 
byces moult seven times. 
VOL. III. oO 
