465 



It is beyond the scope of the present paper to enter into 

 any detailed account of the cyiology of spermatogenesis in 

 Nasonia. 



The Female Organs. 



The ovaries, like the testes, are present in the earliest 

 larvae, a,nd are not to be distinguished from these in any 

 way. There is, therefore, no need to describe them here. 

 Even in the larva at the time of defaecation it would be 

 difficult to determine the sex of the larva, were it not for 

 the presence of the rudiments of the ovipositor, and the 

 absence of vesiculae seminales. The size of testis and ovary 

 is fairly identical; the oogonia measure 5J/x tO' GJ/a in 

 diameter, and, in places, are arranged in little clusters of four 

 cells surrounded by a few coarse, unbranched cells, homol- 

 ogous, perhaps, with the connective tissue network of the 

 testis. The greater number of oogonia, however, do not 

 accumulate in such masses, and the clusters are to be regarded 

 as recently divided cells, which, on account of the rapid cell 

 division, have not had time to separate. The oviduct is also 

 a tube considerably wider than the vas deferens; proximally 

 it is composed of flattened, slightly branched, cells; distally 

 of cubical cells. 



In the larva at about the time of defaecation a slight 

 ingrowth of cells takes place between the first and second 

 pair of ovipositor appendages. In the larva, some sixteen 

 hours later, this ingrowth has become more prominent and 

 is beginning to undergo a certain amount of folding. It is 

 the rudiment of the vagina. When first formed in the defae- 

 cating larva, it consists of loosely arranged epithelial cells, 

 which, however, soon merge closely together. The oviducts 

 do not at this stage open into the vagina, although they 

 terminate close to, and already fit tightly against the in- 

 growing vaginal invagination. The ovaries have now grown 

 into a pair of long spindle-shaped organs, running vertically 

 and lying close beside the metamorphosing intestine; they 

 reach nearly to the dorsal body wall and approach each other 

 closely here, but do not, as yet, show any sign of growing 

 forwards (fig, 154). 



The ovary itself consists of a great mass of oogonia, 

 rounded or hexagonal in shape, and closely packed together. 

 The whole mass is covered with a thin layer of minute cubical 

 cells, continuous with the cells forming the oviduct; while 

 covering the whole ovary is a thin serosa (fig. 187). 



A few hours after the larva has pupated the vaginal 

 invagination grows backwards and begins to extend consider- 

 ably in size, and the two oviducts, which for several hours 



