54 UmversiUj of California Publications. [Entomology 



The cuticle of the wingpad is quite uniform with that of the 

 rest of the body, and is simply continuous, at the base of the 

 pad, with that of the thoracic wall, there being no articular 

 thickenings. When the wrinkles of the veins appear, one can 

 also see signs of the developing hinge structure of the wing. 

 In those insects in which the pupal wingpads are cemented to 

 the body, the cuticle of the inner (ventral) side is much thin- 

 ner than that of the outer (dorsal) side, but there are no 

 differentiations indicating the veins except wrinkles on the 

 dorsal side. 



The increase in size at each molt is provided for by a series 

 of wrinkles of the layers of the hypodermis, in the same way, 

 and to much the same extent, as occurs in other parts of the 

 body. 



Thus we see that up to the entrance upon the pupal condi- 

 tion the development of the wings had not been carried forward 

 any considerable distance. Within the pupal wingpad the 

 organ continues its development in a very leisurely Avay, coming 

 to its perfection only just before the insect is ready to emerge 

 as an adult. The wing just before the last molt is a striking 

 example of close packing. The veins, though composed of 

 thick cuticle, are stowed away so that they occupy only a small 

 fraction of their length when extended. This is accomplished 

 so exactly alike for both the dorsal and ventral faces of the 

 wing that when expanded the two correspond in every detail. 



Since the veins are nearly all produced in two parts it is 

 necessary for their completion when in position after the final 

 expansion of the vein that they superpose with great accuracy. 

 This requires that the cells of each inter venous area shall 

 develop a cuticle of the same size in the two surfaces. This 

 coordination of the two membranes I believe to be brought 

 about by the direct contact of corresponding cells. The fact 

 that the deep ends of the cells composing the two hypodermal 

 layers are united has been figured and described for several 

 groups. In some groups this is supposed to be brought about 

 by the connective tissue, while in others the cells of the two 

 hypodermal layers are figured as actually touching each other. 

 From my own preparations I believe that both methods are to 

 be met with. 



The size of the wing seems to determine to a considerable 

 extent which of the conditions shall be realized. The best 



