The structure of the internal Genitalia of some male Diptera. 531 



and Cholodkovsky (3, p. 392), where both teste s are surrounded 

 by a common dark-red pigmented scrotum. 



The lunien of the testes of different species, has already been 

 described by Cholodkovsky (3). Without entering into details, 

 which are ah'eady known from the descriptions of the species, examined 

 by me, I wish, however, to add the following remarks aboiit the Con- 

 tents of the testes. In most Diptera, examined tili now, the apical 

 cell disappeared already in the imago, which seems also to be the 

 case with other orders of Insects. ChHOLODKOVSKY observed it in 

 La^hria and Asilus and saw traces of it in Musca, Sarcophaga and 

 Scatophaga. I myself have found presumable traces in Eristalis tenax 

 and Syrphus balteatus. For the rest there are in the testes, generally 

 to be Seen older stages of the ontogeny of the germ-cells, the younger 

 stages being fomid in the proximal part and the older distally. Besides 

 these stages, I often observed in the testes degenerated cysts and 

 other elements, of which the function and origin is only to be made 

 out by a thorough investigation of the ontogeny. Perhaps these 

 elements serve for the nutrition of the germ-cells. 



The investments of the vasa deferentia are always an immediate 

 continiiation of the coverings of the testes. If the tunica externa 

 of the testes is pigmented, then this pigmentation may maintain 

 itself over the whole length of the vasa deferentia {Syrphus, Rhingia) 

 or only a short distance, {Eristalis, Sarcophaga, Dexia, Lucilia, Musca) 

 whilst in a few {PoUenia) the pigmentation of the externa of the testes 

 stop suddenly at the commencement of the vasa deferentia. 



In both the Tipulidae examined, the vasa deferentia form 

 a bladder, which seems to have partly a secreting function and also 

 serves as a temporary depository f or spermatozoa. In other Diptera, 

 too, these bladdery widenings of the vasa deferentia may occur 

 (DuFOUR 6, c. f. his figures 123 and 138). 



In Syrphus and Rhingia we see both vasa deferentia appar- 

 ently united to an unpaired vas deferens; apparently, because 

 in this unpaired canal, both epithelium-tubes preserve their inde- 

 pendence. 



The accessorial glands are also invested by two layers: an 

 outer thinner layer and an inner gland-epithelium. This epithelium 

 in several cases {Syrphus, Sarcophaga, PoUenia, Dicranomyia) does 

 not appear as a gland-epithelium, but the contents of the tubes then 

 generally betray the presence of gland-epithelium, because the con- 

 tents are composed of the secreta expelled by the epithelium. In 



