DEVELOPMENT OF THE GENERATIVE ORGANS. 687 



mind is to account for the occurrence of more than a single 

 pair of these rudimentary organs. Ganin's observations on 

 Platygaster, however, appear to be in favour of the existence 

 of two pairs of such rudiments. These groups of cells re- 

 semble the imaginal discs, and are solid ovoid masses of small 

 epithelioid cells measuring '2 mm. in their long diameter. I 

 have no absolute evidence as to their true nature. 



The earliest stage in which I have been able to identify the 

 gonads with certainty is the first day of the pupa state, when 

 they are occasionally seen in sections as ovoid groups of small 

 epithelial cells enclosed in a cellular mesoblastic capsule, which 

 stains more readily than the cells enclosed within it. The 

 long diameter of the capsule is '2 mm. 



FIG. 98. The ovary and testis on the third day of the pupa stage ; from dissections. 

 t, testis ; d, duct of the testis ; o, ovary ; g c, genital cord ; h, hypodermis. Seen 

 with an inch objective. 



On the third day of the pupa I have succeeded in dissecting 

 out both the ovaries and testes, which are now very distinct, 

 and in sections exhibit a marked differentiation of structure. 



The Testis on the third day of the pupa is a glistening white 

 reniform body '4 mm. in diameter. The genital cord is 

 attached to it laterally at the hilus ; this is a slender cellular 

 cord invested by a distinct peritoneal membrane which extends 

 backwards towards the apex of the abdomen ; it subsequently 

 becomes the vas efferens. Its length is about i mm. ; it unites 

 with its fellow at an acute angle, and forms the rudiment of 

 the vas deferens, which is attached to the hypodermis a little 

 in front of the position of the future anus. 



45 



