The structure of tlie internal Genitalia of some male Diptera. 509 



the expelled secreta, betray however the original character of the epi- 

 thelium. Without doubt it has secreted during the larva-stage and 

 lias lost this function in the adult. The fluid produced during the 

 larva-stage appears to be sufficient for the whole life of the imago. 

 Accessorial glands and the unpaired vas deferens come 

 out on a common papilla in the ductus ejaculatorius (fig. 9 d.ej), 

 which is enlarged a little at its beginning. The ductus ejaculatorius 

 runs caudally and then turns to the right side in a cranial direction 

 and ends in the sacculus ejaculatorius (fig. 9 sac), which finds an 

 outlet through the ductus copulatorius (fig. 9 d.cop). Both are 

 lined with a soft chitinous intima and surrounded by a cellular externa. 

 Here, too, the sacculus is provided with a prominence, in which is 

 hidden the apothetes ejaculatorius, which is connected with the 

 wall of the sacculus by transversally striped muscle-f ihres. 



Syrphus balteatus de G. (Fig. 13 and 14). 



In almost all respects the structure of the male genitalia of Syrphus 

 balteatus is equal to that of the Syrphus species I have described above. 

 The abdomen too, shows the same bend at its end. 



In the tunica externa of the testes I have seen no tracheal 

 trunks, but on the outside of it, very intimately against it, I have. 

 Probably however, they will be ramified also in the tunica externa. 

 In the sections I often saw, that the externa was torn off from the 

 tunica propria (fig. 13). Fig. 13 gives a drawing of a longitudinal 

 section of the testes. Proceeding from the proximal part to the 

 distal, we observe different stages of the development of the germ- 

 cells. Besides, I saw a clear mass of protoplasm lodged quite pro- 

 ximally in the blind apex of the testes (fig. 13 a), being probably 

 a remnant of the apical-cell. Near to it are to be seen large nuclei, 

 (fig. 13 hr.c), rieh in chromatin, the same as we have met in Eristalis 

 tenax, evidently the so-called mother brauch cells. Also here 

 mitotical cell-divisions are often to be seen in the different stages of 

 the germ-cells. 



Rhingia rostrata Linn. (Fig. 15 — 19). 

 In fig. 15 we see the structure of the internal genitalapparatus 

 of Rhingia rostrata. It is composed of the testes, each with its vas 

 deferens. The two vasa def erentia meet each other in the median 

 and form together the unpaired vas deferens. This opens, at 

 the same time with two accessorial gland-tubes, into the vesi- 



