621 



stage. The wings proper, are at this time large, well expanded struc- 

 tures being between the larval integument and the hypodermis of the 

 prepupa (Fig. 2). 



A graphic reconstruction of the right side of the mesothorax 

 (Fig. 1) showed that the abnormal structure was nearly circular in 

 outline, attached to the body along the dorsal anterior edge, and 

 closely resembling the wing in its mode of attachment. No trace of 

 veins and only a few minute tracheoles were discovered in the cavity 



AL- 



ALS 



ALS 



Fioj. 2. P. rapae. Transverse section through mesothorax. AL, normal wing. 



ALS, supernumerary wing. Ti?, trachea. CT.t/, cuticula. ITDi? il/, hypodermis. 



INT, intestine. CD, heart. G LS, spinning glands. NS, ventral nerv chain. 



PD, legs. B. & L. 2 in obj. 2 in oc, 160 mm. 



of this abnormal wing. Its position upon the body is well shown in 

 Figure 2. It is situated rather low down on the pleural area being 

 somewhat below the joint where the wing discs originate. 



The structure consists of a single layer of hypodermal cells of 

 nearly uniform thickness (Fig. 3) and without any indications of 

 further modifications. It was, however, too early in the life of the 

 individual to find any trace of scales or other imaginai structures. 



