NO. 2 ENCYCLOPEDIA OF INSECT ANATOMY — SNODGRASS I5 



tion may take place in organs that are not affected by the living con- 

 ditions imposed on the embryo or the larva. 



Moulting: The physiological process of separating the body cuti- 

 cle from a new cuticle being formed beneath it by the epidermis. 

 How this separation is accomplished is uncertain but it is soon made 

 more obvious by the secretion from the epidermis of a moulting 

 fluid which digests a greater or lesser amount of the old cuticle while 

 the new cuticle is being secreted. The terms moulting and ecdysis 

 have often been confused, with, as one result, the naming of the 

 moulting hormone as "ecdyson." Ecdysis, q.v., is literally the com- 

 ing out of the insect from its moulted cuticle, and is not dependent 

 on any hormone. 



The phonetic spelling "molting" which recently has become cur- 

 rent in the U. S. A. is not justified by the derivation of the word 

 from the Latin mutare. The "u" is clearly the essential vowel, and 

 it is retained in other languages, as mudare in Italian and mudar in 

 Spanish and Portuguese. 



Ecdysis: The word is derived from the Greek word meaning 

 "coming out." It is properly pronounced ek'-di-sTs but is commonly 

 heard as ek-dy'-sis. The word has commonly been defined as synony- 

 mous with moulting, but the word can mean only the shedding or 

 coming out of the moulted cuticle by the insect. Very commonly the 

 newly moulted insect remains within the old cuticle for a variable 

 length of time before emerging. With some insects, as the honey 

 bee, the pupa goes through its preliminary change from the larval 

 form within the last larval cuticle and comes out only when it has 

 attained the final external form of the pupa. The most extreme 

 case, however, is in the muscoid flies which form a puparium from 

 the third larval cuticle, undergo the pupal stage within this, and then 

 the adult emerges from it. 



The insect within the moulted cuticle of the previous instar is the 

 pharate (cloaked) period of the larva, pupa, or adult (Hinton, 1958). 



Alimentary canal: The food tract of the mature insect always 

 consists of three parts serially continuous but of different origins. 

 The middle part, the mesenteron, represents the primitive endodermal 

 stomach or archenteron of the gastrula; the anterior and posterior 

 parts, the stomodaeum and proctodaeum respectively, are secondary 

 ingrowths of the ectoderm. The origin and relations of the parts, 

 however, are obscured in the development of the embryo by the 

 various ways in which gastrulation takes place (see Gastrulation), 



