The striicture of the internal Genitalia of some male Diptera, 527 



consist of different stages of the development of the germ-cells, 

 e. g. cytocysts, gonocysts and spermatocysts. Besides these, 

 bundles of ripe spermatozoa are to be seen (fig. 64 sp). 



The vasa deferentia begin caudally in the testes and are 

 invested by an epithelium, exactly like that of the testes. They 

 run caudally (fig. 63 vd) without twisting or bending and expand 

 suddenly to a bladder, just as we have seen in Tipula. The bladder 

 is lined by a flat epithehum, which shows traces of being a gland- 

 epithelium. Above the nuclei, on the side turned to the lumen, T saw 

 protoplasmatic protuberances (fig. 65 in), so that here the suspicion 

 occurred to me, that the cells have been secreting in a younger stage 

 and that this function has ceased. The outer investment (fig. 65 ex) 

 of this bladder is formed by a thin layer containing flat nuclei. In 

 the lumen of the bladder there are only spermatozoa (fig. 65 sp) 

 to be seen. After having passed the bladder, the vasa deferentia 

 continue their way in a caudal direction, but they are more voluminous 

 and besides, this part is shorter than the cranial part before entering 

 the bladder. The epithelium, by which it is lined, is exceedingly flat 

 (fig. 66). 



The accessorial glands (fig. 63 acc) are rather short tubes, 

 filled up by a strongly staining liquid. The epithelium (fig. 67) of 

 these gland -tubes is also exceedingly flat and does not in any way 

 remind me of a gland-epithelium. Here, too, the secreting function 

 must have ceased in the imago, so that the secreta, with which the 

 tubes are filled up, are produced during the larva-stage. The tunica 

 externa of the gland -tubes is only very thin. 



Vasa deferentia and accessorial glands meet in the median 

 and end together on a common papilla in the caudal part of the vesi- 

 cula seminalis (fig. 63 ves), having each tube its own orifice. The 

 vesicula seminalis is a very big and blind sack, extending in a 

 cranial direction, which is invested bya tunica externa and interna. 

 The externa is thin and provided with flat nuclei (fig. 68 ex). Tha 

 interna isa columnar gland-epithelium. The epithelium-cells (fig. 68) 

 are often separated by rather large, but less discernible intercellular 

 fissures. The cells are provided with round or oval nuclei, situated 

 at the base. On the inner surface of the epithelium, I saw a seam, 

 which probably was caused by the secreta expelled. In some of these 

 epithehum-cells I discerned large vacuoles, containing a dark staining 

 substance, and in some places, I saw them being expelled. I have 

 not been able to observe spermatozoa in the vesicula seminalis. 



