THE METAMORPHOSIS. 425 



it; for if the new skin already existed beneath the old one, must it not 

 there exist in considerably smaller compass rather than in larger ? 

 That Kirby and Spence could adopt and explain this opinion as the 

 most correct, distinctly fixes their position in physiology, which, not 

 merely here, but almost everywhere, exhibits itself as an antiquated 

 one. Whereas, according to Herold's * admirable observations, there 

 is not the least trace in the young larva of the new skin, but this first 

 originates towards the end of the first period of the caterpillar's life, a 

 few days only before the old one is stripped off. It is then observed 

 that the mucous and muscular layers of the skin separate all round 

 from the epidermis, and then clothe themselves upon the superior 

 surface with a new epidermis. The development of this new external 

 skin occupies two or three days, during which the caterpillar appears 

 sickly and takes but little or no nourishment. Lastly, the old skin 

 divides longitudinally along the back, and the caterpillar frees itself 

 from its now separated skin by means of contortions and violent 

 motions, first emancipating its head and then drawing the body out. 

 The epidermis, all the external visible organs, and even the mandibles 

 and palpi, remain attached to the old skin. Upon the caterpillar 

 having quitted its old case, it appears very languid, its body is soft and 

 easily injured, so that during its change of skin even a slight pressure 

 is sufficient to kill or wound them, but it speedily resumes its former 

 strength^ and it then devours with renewed voracity, as if eager to make 

 up for lost time. Contemporaneously with the formation of the new 

 skin, the intestinal canal has also enlarged, thence after its moulting 

 the quantity of food becomes greater, the digestion more perfect, and 

 the formation of the fatty mass is more rapid and in larger quantities. 

 In general, this first moult takes place about the twelfth day of the 

 life of the caterpillar. The second moulting, which occurs after another 

 lapse of from six to eight days, presents the same phenomena, and has 

 the same effects ; and the third also, which takes place after another 

 six or eight days. But its voracity constantly increases, so that a 

 larva does not now merely consume three or four times its own weight 

 of food, but it also increases considerably in corporeal mass ; as, for 

 instance, the comparative weight of a full-grown caterpillar of the goat 

 moth to that of the young one just crept out of the egg is, according to 

 Lyonet, as 72,000 to 1. A growing flesh-fly takes in twenty-four 



* Entwickelungsgeschichte der Schmctterlinge, p. 26, &c. 



