PROCESS OF MOULTING 



609 



The growth is most rapid after the last moult. "Thus a larva of Sphinx 

 ligustri, which at its last change weighed only about 19 to 20 grains, at the ex- 

 piration of eight days, when it was fully grown, weighed nearly 120 grains." 

 (Newport.) 



d. The process of moulting (ecdysis) 



Insects periodically shed the exoskeleton, together with the chi- 

 tinous lining of their internal organs of ectodermal origin, which 

 thus sloughed off are called the exuvia. The process in the locust 

 has been described by Riley. 1 It occupies from half to three- 

 quarters of an hour (Fig. 565). This process has naturally, from 

 the ease with which it can be observed, been most frequently 



Fio. 565. Process of moulting 1 from nymph to imago in the locust (.I/. pretus) : a, nymph with 

 skin just split on the back ; b, the imago drawing itself out, at o, nearly free ; d, the imago, with 

 wings expanded ; e, the same with all parts perfect. After Riley. 



examined in the Lepidoptera, though careful and detailed observa- 

 tions of the inner and outer changes are still greatly needed, espe- 

 cially in other orders. In the caterpillar of most moths, especially 

 one of the more generalized bombycine moths, on slipping out of 

 its egg-shell the head is of enormous size as compared with the body, 

 but the latter soon fills out after the creature has eaten a few hours ; 

 the head, of course, does not during this time increase in size, and 

 the larvae of different instars may be exactly distinguished, as Dyar 

 has shown, by the measurements of the head. 



Before the caterpillar moults, it stops feeding, and the head is 

 now small compared with the body; the head of the second instar 

 is now large, situated partly under the much-swollen prothoracic 

 segment, and pushes the head of the first instar forward. 



Newport has well described the mode of shedding the skin in 



First Rep. U. S. Ent. Commission, p. 281-283. 



2 R 



