The structure of the internal Genitalia of some male Diptera. 521 



with their distal ends, which continiie in the vasa deferentia, (fig. 51 

 vd), so that they are placed witli their longitudinal axes transversally 

 in the abdomen. The testes are ei:iclosed by fat-body-tissue, 

 which at several places is intimately grown together with the testes. 

 The outer Investment of the testes^ the tunica externa, (fig. 52 ex), 

 is an intensively brown pigmented cell-layer of a variable thickness, 

 in which I have seen tracheal trunks. The lining, the tunica propria, 

 consists of epithelium, which becomes higher at some places (fig. 52 in) 

 without, however, there being a question of cellular septa. Also in 

 the blind proximal apex of the testes, the epithelium is developed 

 as such, so that in PoUenia rudis amembrana propriais not formed. 

 Here the development of the germ-cells in the adult has already 

 made so much progress, that in the lumen of the testes nothing but 

 ripe spermatozoa are to be found. 



The vasa deferentia (fig. 51 vd) are very short tubes, which 

 run straight to the median and thus occupy a transversal Situation 

 in the abdomen. Both their investments are an immediate continuation 

 of the tunica externa and interna of the testes. The pigmen- 

 tation stops on the testes, at the beginning of the vas deferens. 

 The externa is very thin and is provided with very small nuclei 

 (fig. 52 vd). 



The accessorial glands (fig. 51 acc) are short tubes, which 

 commence cranially with regard to the testes and are situated ventrally 

 of the gut, a little on the left in the abdomen. They run caudally 

 without making any important bends (fig. 51 acc). They are composed 

 of two cell-layers. The tunica externa is membraneous, that is 

 to say, nuclei are very difficult to discover in it. The interna (fig. 53) 

 is a flat epithelium, which does not in any way give the impression 

 of a gland-epithelium. Yet I must presume this, because the acces- 

 sorial gl and -tubes are filled up with a weak colouring fluid, which 

 however, must have been secreted by the gland-epithelium during the 

 larva-stage. Near the end, the accessorial gland -tubes become 

 narrower (fig. 51 acc). 



Vasa deferentia and accessorial glands open together into 

 the du et US ejaculatorius on a common papilla. The orifices of 

 the vasa deferentia on the papilla are situated cranially to those 

 of the accessorial gland -tubes. (In my scheme fig. 51, this Situa- 

 tion is not shown.) 



The ductus ejaculatorius (fig. 51 öJ.e/), which begins about in 

 j the middle of the abdomen, runs caudally but also towards the left 



