17f) INSECT TRANSFORMATIONS. 



will very distinctly see their several branches and 

 ramifications, cind also their ring'ed structure*." 



The caterpillars of moths and butterflies generally 

 cast their skins five times ; but some cast them seven 

 and even ten times, as in the case, according; to 

 Cuvier, of the great tiger-moth {Ai'ctia Caja, Ste- 

 phens). By the breeders of silk-worms this natural 

 process is ranked among their maladies ; and not alto- 

 gether without reason, as it frequently proves fatal, 

 from causes to which we have already alluded. For 

 several hours, often for a whole day, after casting the 

 skin, the caterpillar continues sluggish and moves 

 little ; and as the vessels are still replete with the fat 

 previously absorbed, there is no stimulus for it to eat. 

 But as soon as this supply is exhausted, it com- 

 mences again to eat voraciously, in order to supply 

 another store of fat for its succeeding moult. 



The moulting of caterpillars, it may be remarked, 

 bears but a slig-ht resemblance to the casting of the 

 feathers in birds, and the hair in quadrupeds. Birds 

 generally cast their feathers once, and many twice, 

 a-year, namely, in autumn and in springt; and 

 quadrupeds in a similar way cast their hair. But 

 in both these cases the process is gradual, and 

 resembles that of shedding the milk-teeth when the 

 jaw enlarges. All of these changes, hov/ever, pro- 

 duce considerable derangements in the animals ; and 

 they are seldom accomplished without disordering 

 health, and sometimes endangering life. The great 

 difference between the changes iu insects and the 

 other classes of animals evidently urises fi"om the 

 difference of their internal structure. It must be 

 obvious to all, for example, that the human body 

 wears. As old age advances the bones waste away 

 and become smaller, the muscles and skin shrink and 



* Svvammeidam, Bib. Nat. vol. i. p. 135. 

 + Teinminck, Manuel d'Ornilhol. Iiitr 



