28 



Studies in the Hybrid Bistoiiinae. IV 



Let us consider for a moment the cause of this. These valves lie 

 free in the abdomen and are quite shut off from any connection with 

 the exterior; yet, to judge from their armature of hairs, one would look 

 upon them as ectodermal in character. 



In development, they arise from a body first dissected out by Herold 

 years ago. This little body or corpuscle, whilst apparently simple in 

 structure, is duplex in origin ; one part arises as an invagination of the 



D'D' = 2nd pair of rods. 

 : Ostium. S = Signum. 



Fig. 6. 

 B = Bursa copulatrix. DD = l8t pair of rods. 

 7= Valve enclosed in pupal covering. 0- 



J7= Uncus. F= Valve. 



posterior margin of the 9th abdominal segment and is therefore dermal 

 in derivation. On the contrary, the remaining portion is not of such 

 origin as it develops from a group of cells at the base of the larval 

 genital ducts. 



From the invaginated cells, ectodermal in character, are evolved the 

 two valves which are consequently dermal structures as might have been 

 determined otherwise from a- consideration of their vestiture of hairs 

 and bristles. The other section of the corpuscle, not of dermal origin, 



