136 



TEXT-BOOK OF ENTOMOLOGY 



represents a wing of a larva three days before pupation, with the 

 germ of a thoracic leg. 



A. G. Mayer has examined the late development of the wings in 

 Pieris rapce. Fig. 149 represents a frontal section through the left 



FIG. 148. Graber'.s diagrams for explaining' the origin and primary invagination of the hypo- 

 dermis to form the germs of the leg (b), and wings (/, A-C), and afterwards their evagination />, 

 so that they lie on the outside of the body. E, stage B, showing the hypodermal cavities (/) and 

 stalks connecting the germs with the hypodermis (z). After Graber. 



wing of a mature larva and shows the rudiment of the wing, lying 

 in its hypodermal pocket or peripodal cavity. How the trachea 



passes into the rudimen- 

 tary wing, and eventually 

 becomes divided into the 

 branches, around which the 

 main veins afterwards form, 

 is seen in Figs. 144, 147, 159. 

 The histological condi- 

 tion of the wing at this 

 time is represented by Fig. 

 ir>l, the spindle-like hypo- 

 dermal cells forming the 

 two walls being separated by the ground-membrane of Semper. 



" While in the pupa state," says Mayer, " the wing-membrane is 

 thrown into a very regular series of closely compressed folds, a single 

 scale being inserted upon the crest of each fold. When the butter- 



Kn.. 14'.'. --Section lengthwise through the left wing 

 of mature larva in /'/v/-/\ r<i/i(e : t, trachea; hyp, hypo- 

 di-rmis ; c, cuticula. After Mayer. 



