The structure of the internal Genitalia of some male Diptera. 523 



cysts, whilst in the distal part I have only discerned ripe sperma- 

 tozoa (fig. 48). 



The vas deferens (fig. iSvd) is formed by an imniediate con- 

 tinuation of the coverings of the testes, but the pigmentation stops 

 very soon and then the tunica externa appears much thinner. 



The diictus ejaculatorius (fig. 4:7 d.ej) is a very long tube, 

 twisted and bended many times, which runs caudally, then turns 

 cranially and runs dorsally over the gut, to end at last in the sacculus 

 ejaculatorius (fig. 47 sac). It is composed of two parts: a voluminous 

 part and a narrower one, of which the difference in histological structure 

 is very striking. I have not been able to discover a tunica externa 

 on the ductus ejaculatorius. The first enlarged part of the ductus 

 ejaculatorius has a very peculiar construction. Its epithelium 

 consists of almost empty cells (fig. 49 xi), in which only the nuclei are 

 remaining and sometimes a little protoplasm, which in this case is 

 visible against the walls of the cells. If we view the cells on the out- 

 side (fig. 49 B), we discern that they are big, polygonal, mostly hexa- 

 gonal cells. Here we have a very remarkable example of exhausted 

 cells; an example I have no where eise discovered in the other Diptera 

 exaniined. It might be supposed that the Contents of the cells would 

 have been dissolved by the various Operations, but this hypothesis 

 does not recommend itself to me, as I have investigated very dissimilar 

 specimens of these species, and in none of them have observed a single 

 gland-cell intact, a thing which it surely were but natural to expect, 

 if the gland-cells were still active. 



The distal part of the ductus ejaculatorius also possesses a 

 wall of gland-epithelium, which is normally developed and is also 

 formed by rather large cells, which are still active (fig. 50). 



The sacculus ejaculatorius is provided with the already 

 mentioned apothetes ejaculatorius and opens out by the ductus 

 copulatorius (fig. 47 d.cop). These organs show the structure, already 

 described before. 



Farn. Tipulidae. 

 Ti'pula oleracea Linn, (Fig. 55 — 62). 

 DuFOüR has already examined the male genitalia of Tipula ole- 

 racea and also sketched these organs (6, pl. III, fig. 25 and 26). I have 

 borrowed my fig. 55 from the figure drawn by him, but mine is some- 

 what modified. We observe that the male gonads of Tipula oleracea 

 consist of the following parts: the two testes with their vasa defe- 



