The structure of the internal Genitalia of some male Diptera. 511 



the iinpaired vas deferenson either side of it and lie very intima- 

 tely pressed against the wall of the vesiciila seminalis. The acces- 

 sorial glands are siirroimded by an exceedingly thin externa, while 

 they are lined by a very high gland-epithelium, the cells of which are 

 sometimes separated by intercellular fissures. The niiclei (fig. 18) of 

 these gland-cells are small, the cells being of a different height, so that 

 the lumen of the gland-tube becomes very irregulär and it seems 

 that the gland-epithelium is folded. 



Accessorial glands and unpaired vas deferens open into 

 a common papilla at the base of the vesicula seminalis (fig. 15 ves). 

 This is a rather large sack, which is blind at the cranial side and con- 

 tinues caudally in the ductus ejaculatorius {iig. 16 d.ej). The 

 wall of the vesicula seminalis is composed of two layers. The 

 tunica externa (fig. 19 ex) is very thin and is provided with flat 

 nuclei. Besides I saw in the externa a delicate longitudinal striping, 

 therefore it is probable, that muscle-fibres are to be found here, The 

 interna (fig. 19) is a gland-epithelium, which however, in the cases 

 examined by me, had already ceased its secreting function. Only the 

 nuclei arround it some remainders of protoplasm, were left of the 

 cells of the epithelium. I got the Impression of these being empty cells, 

 which distinctly proved that gland-epithelium was present here. It 

 is Strange, however, that in the lumen of the vesicula seminalis, 

 no trace of a fluid or of spermatozoa is to be seen, though it is likely 

 enough that they were already expelled during possible copulation. 

 I could not prove if the name vesicula seminalis is justified here, 

 (because I did not find spermatozoa) but I have given this name 

 to this cranial blind sack in analogy with the male gonads of 

 Eristalis. 



The ductus ejaculatorius {i\g.\bd.ej) bends cranially and 

 opens into the sacculus ejaculatorius (fig. 15 sac), which finds an 

 outlet through the ductus copulatorius (fig. l^d.co'p). The struc- 

 ture of the sacculus and ductus copulatorius is the same as with 

 the specimens described above, whilst there is also an apothetes 

 ejaculatorius to be found. 



If we now briefly examine the structure of the gonads in Rhingia, 

 comparing it with its relations Eristalis and Syrphus, we find that 

 Rhingia, possessing both a vesicula seminalis and an unpaired 

 vas deferens, combines the characteristics of Eristalis and Syrphus. 

 Whether the Rhingia-type is primary or secundary, in other words, 

 whether it is to be derived from Eristalis and Syrphus or inversely, is 



