The Development of the Wings of a Caddis-fly Platyphylax designatus Walk. 575 



LüBBEN (7) shows a dorsal view of a larva of Plectrocnemia 

 conspersa with the wing rudiments on one side. He has also drawn 

 part of a transverse section of the pupa of Philopotamus ludificatus; 

 in this one section is shown the prothoracic stigma and also a wing 

 rudiment which has apparently just become external. 



It is imcertain at what stage in the development of Platyphylax 

 designatus the wing rudiments first appear; in the present work the 

 ecdyses were not followed and the number of moults a larva of a certain 

 length has passed through is not known. Sections of larvae that had 

 just emerged from the egg, and of others several days old, failed to 

 show any change or modification in the hypodermis at those places 

 where the wing rudiments would later appear. This does not hold 

 true of the cuticula which shows, even in the youngest larvae, a small 

 slightly darkened area external to that part of the hypodermis which 

 will show the first change at the beginning of wing development. This 

 darker area of the cuticular layer which lies over the wing rudiment 

 is not noticeable, externally, in a newly hatched larva and to find it 

 one has to examine transverse sections of the meso- and metathoracic 

 Segments. These darkened areas of the cuticula are very noticeable 

 in the older larvae and one can easily trace them from the old to the 

 very youngest larvae thus leaving no doubt that the position of the 

 wing rudiment is discemable on the cuticula before it can be noticed 

 in the underlying hypodermal cells. 



Having obtained and preserved a number of eggs of Platyphylax 

 designatus an endeavour was made to find some trace of the wing 

 rudiment in the embryo; several of these, both in early and late stages, 

 were sectioned but no indication of a wing rudiment could be found. 

 An examination of the two principal works on the embryology of the 

 Trichoptera showed that neither Zaddach (17) nor Patten (12) found 

 any trace of a wing rudiment in the embryos of the species of caddis- 

 fhes with which the}^ worked. 



Not having followed the ecdyses of the larvae it was necessary 

 to adopt some method for determining, roughly, the comparative ages 

 of the specimens studied ; this was done by measuring each larva before 

 it was studied or sectioned. Such a method proved very unsatisfactory 

 and allowed of a comparison which could not be accurate. The larvae 

 were measured before being used and no allowance made for differences 

 which might arise from varying degrees of contraction or from 

 the use of different preserving fluids. Another serious objection to 

 this method lies in the fact that larvae of the same length may show 



