10 Journal New York Entomological Society. ;v„i. viii. 



Pancritius thinks it is and figures it as a thick layer of chitin with 

 the same structure as the outside cuticle of the body. Gonin thinks 

 it is not formed at all until the latter part of the last larval stage. In 

 Sanniuoidea exitiosa (Fig. 20, /V) there is no doubt of a definite layer 

 of cuticle surrounding the wing. In Aiitomeris io there is a much 

 more definite layer of cuticle ; this is true in an early stage, even be- 

 fore the proliferation of the tracheae (Fig. 21, r). The tracheoles 

 alone are functioning at this period. The thick hard cuticle in this 

 specimen may be traced quite a distance into the invagination ; and it 

 will be noticed that it gradually thins and finally l^ecomes very thin 

 and delicate. Iri Pieris the layer of cuticle extends in the form of a 

 plug as described in the discussion of the first period, and the wing- 

 bud is not surrounded by a chitinous layer until the fifth stage when a 

 very thin, delicate, structureless membrane of cuticular nature appears 

 which is destined to become the cuticle of the wing of the pui)a. 



The Ori(;ix of ihe Cuticle. 

 My observations indicate that the cuticle is a product of a trans- 

 formation of the outer ends of the hypodermal cells instead of a secre- 

 tion thrown out from these cells. By the use of chitin stains, the 

 chitinous nature of the ends of the cells in the pu|:)a wings (Fig. 35, c~) 

 is brought out. As more evidence that it is not a secretion, the cuticle 

 in the development of the prepupal wing (Fig. 28, pc) is seen to 

 gradually decrease in density as it approaches the hypodermal cells 

 and gradually fades into the cells themselves. These facts have been 

 observed many times and in many places upon the insect other than 

 upon the wings, during the course of this investigation. 



Several observers have noted that the cuticle is often divided into 

 polygonal areas corresponding to the subadjacent hypodermal cells. 

 It is not probable that this would be the case if the cuticle were a se- 

 cretion thrown out from the cells ; for in such a case the products of 

 the different cells would naturally merge into a continuous layer. 

 But the formation of a cuticle by a transformation of the outer por- 

 tions of the body of the cells would result in the formation of such 

 areas. 



Ordinarily this division of the cuticle into areas is not \ery evident 

 in sections. But in the case of one larva of Sanniuoidea exitiosa the 

 areas were remarkably distinct : so much so that the sections of the 

 cuticle broke up into little blocks corresponding to the hypodermal 

 cells (Fig. 37). 



