STATES OF INSECTS. 201 



sirous now to bespeak your attention, — the Growth, I 

 mean, and size of Insects in this state. As to size, larvae 

 differ as much as insects in their perfect state : these last, 

 however, never grow after their exclusion from the pupa, 

 while larvae 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 caterpillar of 

 the great goat-moth (Cosstis ligniperda F.) after having 

 attained its full growth is at least 72,000 times heavier 

 than when it was first excluded from the egg a ; and of 

 course had increased in size in the same proportion. 

 Connected with the size of larvae, 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 itselfj till, becoming too big 

 for these solid parts, nature restores the equilibrium be- 

 tween them by a fresh moult b , 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 c . 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 unconfmed, so that, when this com- 

 pression is removed, the soft and elastic new integu- 



a Lyonnet 11. h JV. Diet. d'Hist. Nat. vi. 290. 



e He BombycihiiS) 68. 



