METAMORPHOSIS IN LEPIDOPTEPA. 



allied compounds. The chitin, he says, is nitrogenous, but it is not 

 related at all to these, and is got rid of because it is effete, just as animals 

 shed their hairs, &c, and because it has served its purpose and is no 

 longer useful. He adds that he " has no doubt that chitin is formed 

 out of fresh nitrogenous material and not out of waste or effete 

 material." The objects of moulting, he states, are : (1) Increase of 

 size. (2) To get rid of material that is effete as a cutaneous covering, 

 and secure a new and active one (internally as well as externally). 

 (3) As an acquired use to obtain change of plumage, change to pupa, 

 &c. As regards the effeteness of the cast skin of the larva,, it may be 

 well to note here that many larvae eat their cast skins, showing that it 

 is a loss of elaborated (not waste or effete) material, that they can ill 

 spare, and some larvae, e.g., the Cerurids, at least in captivity, do badly, 

 or die, if deprived of their cast skins. When the moulting takes place, 

 not only is the exoskeleton shed but also the chitinous linings of all 

 the internal organs which have had an ectodermal origin. 



Before the larva moults it stops feeding, and usually (at least in the case 

 of the exposed -feeding lepidopterous larvae) spins a silken pad, into which 

 the hooks of the prolegs are firmly fixed. At this time, the larva seems 

 to draw upon its stored food (the fat-body) and the hypodermis secretes 

 a fresh supply of chitin beneath the old cuticular envelope. At the 

 same time the old cells beneath appear to become disintegrated and to 

 produce a lubricating fluid between the new and old skins, which 

 greatly aids in the process of exuviation ; the external envelope now 

 dries, becomes wrinkled and much contracted in length, being gradu- 

 ally separated from the new and very delicate one beneath. Trouvelot 

 explicitly says that in Telea polyphemus the old skin "is detached by a 

 fluid which circulates between it and the worm (larva) . ' ' 



Newport describes the moulting of the larva of Sphinx lic/ustri, 

 stating that, after several powerful efforts of the larva, the old skin 

 cracks along the middle of the dorsal surface of the mesothoracic seg- 

 ment, and by repeated efforts the fissure is extended into the prothorax 

 and mesothorax. The larva then gradually presses itself through the 

 opening, withdrawing first its head and thoracic legs, and subsequently 

 the remainder of its body, slipping off the skin from behind like the 

 finger of a glove. This process, after the skin has been once ruptured, 

 seldom lasts more than a few minutes. When first changed, the larva 

 is exceedingly delicate, and its head, which does not increase in size 

 until it again moults, is very large in proportion to the rest of the 

 body. Chapman states that in the larval moults (larva to larva) of 

 Sphinx lir/ustri, the head remains in one piece and rarely remains 

 attached to the rest of the skin. It contains the mouth-parts of the 

 new head and fluid. This is probably licked up by the larva at the 

 moult. The old head often falls off, but if not, the larva rubs it 

 against its foothold, or side, until it does so. Sometimes, in captivity, 

 owing to weakness of the larva, Ac, it does not rub it off, and it 

 remains on. If it does so until the new head hardens, and one then 

 removes it, one finds that it has restricted and deformed the new 

 mouth-parts, especially the jaws, so that the larva cannot feed. In a 

 larval moult, the skin usually remains attached by the prolegs, and the 

 Lxrva, as it were, creeps out of it. At the pupal moult, the larval 

 skin slowly passes backwards, collecting in a heap at the anal 

 segment. 



