184 CHARLES T. 13RUES. 



Thus the causes must be such as affect the wings alone. It seems 

 therefore that we may be justified in saying that it is the result of 

 certain mechanical influences of the environment affecting the 

 wings alone, which causes their loss. This may be accomplished 

 either by hindering the organism in its movements l or by laying 

 it open to removal from its proper environment. 2 



FIRST CATEGORY, "PUPAL" WINGS. 



Where the development of the wings proceeds normally up to 

 the formation of the pupa and is then suddenly arrested, the 

 adult wings resemble those of the pupa in general detail and 

 form except that they are more heavily chitinized. They oc- 

 cur in certain flies belonging to the family Phoridae 3 and indi- 

 cate the first step toward their total atrophy. The species with 

 this form of wings resemble more closely in other morphological 

 details fully winged forms than do their relatives whose wings 

 fall into the second and third categories. 



The cases of wingless grasshoppers afford beautiful examples 

 of this persistence of the wing character of the previous instar. 

 In these Orthoptera the wings of subapterous species cannot be 

 distinguished from those of the earlier instars of fully winged 

 species by structure alone. Were it not for the fact that there 

 is a reversion of the relative positions of the two pairs of wings 4 

 at the last ecdysis one could not decide from a mere examina- 

 tion of the wings whether a certain form is larval or adult. 



Enipyris subaptcnts M. et B. MSS., 9 (Proctotrupidae) (Fig. 2). 

 The wings of this species, like those of many other Procto- 

 trupidse, are very short, but still retain a nearly normal system of 

 neuration. The wing membrane has been lost, while the vena- 

 tion remains undisturbed. This gives the wings a distinctly 

 pupal character. 



1 That the wings are an inconvenience to life under certain conditions is evinced by 

 the well-known fact that the fertile queens of ants actually tear off the wings on be- 

 ginning their underground life. 



2 In the cases of insects inhabiting small oceanic islands, mountain tops and deserts, 

 the possible habitat for a species is usually very limited. 



3 Notably the genera Psyllomyia Lw. and Commoptera Brues. 



4 In all instars except the last, the posterior wings lie above the anterior ones, 

 which position is reversed in the adult. 



