The structure of the internal Genitalia of some male Diptera. 513 



propria. In the blind proximal part I sometimes saw transversal, 

 very thin cellular septa radiating from the epithelium and pushing 

 into the lumen of the testes. In some specimens, on the blind cranial 

 apex of the testes, there is to be found a protuberance, which is likewise 

 separated from the remaining contents of the testes, by a septum 

 (fig. 22). In this part I saw gono-orcytocysts. In other specimens 

 this protuberance was not to be seen, but I found in the cranial apex 

 of the testes a part, separated by a septum and filled up with the 

 same cysts. The remaining contents of the testes may be distin- 

 guished into two parts (fig. 23) : a darkly coloiuring outer layer, com- 

 posed of nothing but bündle wise grouped spermatozoa, and a lightly 

 colouring axis, which is filled up with dispersed spermatozoa and 

 between them dispersed cells, which have a degenerated character 

 (fig. 23 y) and which seem to float in a fluid. I found these cells also 

 near the gono- and cytocysts, when present, in the cranial apex 

 (fig. 23 y) and they very strongly gave me the impresion of being 

 degenerated gono- or cytocysts, whilst I suppose the fluid to derive 

 from the degenerated cysts or partly from the other elements of the 

 developing-link of the germ -cells. Cholodkovsky, however, sup- 

 poses them to be >>Nährzellen << of the testes and to be derived from 

 the epithelium-septa (3, p. 395). A single time I saw vacuoles in the 

 inner part of the testes and it is peculiar, that those degenerated 

 cells group arround them, so that one gets the wrong Impression of 

 there being a small canal in the testes. In most specimens (I examined 

 about ten) I saw no trace of younger stages of the ontogeny of the 

 germ -cells, consequently the development of the spermatozoa 

 had already come to an end. 



Both investments of the testes continue immediately on the 

 vasa deferentia, These run caudally at the beginning, without 

 making windings, bend themselves and then run straight in a cranial 

 direction very close against each other, tili they have reached about 

 the height of the testes (fig. 22 vd). Here they bend once more and 

 remain running in a caudal direction side by side, but at the same time 

 they have got an entirely different character. They have strongly 

 increased in size. The tunica externa of this part of the vasa 

 deferentia remains unaltered, but their lining has received an other 

 structure and has become a gland-epithelium (fig. 24 in). The epithe- 

 lium seems to be folded. Between these foldings there are to be seen 

 very small radial fissures, which are very difficult to discover (fig. 24 r). 

 All these radial fissures come out in the central lumen (fig. 24 l). Thi 



