194 STATES OF INSECTS. 



merdam is the true one, we may imagine that the enve- 

 lope that lies within all the rest is that which covers the 

 insect in its pupa state. Above this are placed several 

 others, which successively become external integuments. 

 These changes or casting of the skin in larvae, 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 twelve days from its 

 birth, and the three next each at the end of half that time 

 from the moulting which preceded it. With some ex- 

 ceptions a , 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 (Arctia villica), nine (Callimorpha 

 Dominula), or even ten times; for so often, M. Cuvier 

 informs us, the caterpillar of the tiger-moth (Callimorpha 

 Caja) casts its exuviae. 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 (Phalcena L.) change four b . The periods 

 that intervene between each change depend upon the 

 length of the insect'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 



a Those Diptera whose metamorphosis is coarctate (Vol. I. p. 67), 

 bees, the female Cocci, &c. do not cast their skin in the larva state. 

 Reaum. iv. 364. N. Diet. d'Hist. Nat. xx. 365. 



•> N. Diet. d'Hist Nat. vi. 289. xx. 372. Cuvier Anat. Comp. ii. 

 548. M. Cuvier (Ibid. 547.) asserts, that most jPapiliones and Bom- 

 byces moult seven times. 



