176 INSECT TRANSFORMATIONS. 



branches and ramifications, and also their ringed struc- 

 ture.'* 



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 {Arctia 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, 

 Irom 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 previ- 

 ously absorbed, there is no stimulus for it to eat. But 

 as soon as this supply is exhausted, it commences 

 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 slight 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 spring;! and quad- 

 rupeds in a similar way cast their hair. But in 

 both these cases the process is gradual, and resem- 

 bles that of shedding the milk-teeth when the jaw 

 enlarges. All of these changes, however, produce 

 considerable derangements in the animals; and they 

 are seldom accomplished without disordering health, 

 and sometimes endangering life. The great differ- 

 ence between the changes in insects and the other 

 classes of animals evidently arises from the differ- 

 ence of their internal structure. It must be obvi- 

 ous 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 



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

 t Temminck, Manuel d'OrnithoI. Intr. 



