512 P. E. Keuchenius, 



a difficult thing to decide, but I am inclined to think the latter hypo- 

 thesis the more probable. 



Farn. Leptidae. 



Leptis scolopacea Linn. (Fig. 20 — 25). 



The male genitalapparatiis of Leptis scolopacea is composed of 

 one pair of testes, vasa deferentia^ ductus ejaciilatorius and 

 sacculus ejaciilatorius (fig. 20 and 21). Accessorial glands 

 are absent, but we shall presently see, that other organs have taken 

 over their functions. 



The testes (fig. 21 f) are a pair of white bodies, varying from 

 oblong to round. Their white colour is owing to the far-body-tissue, 

 by which they are enclosed. This fat-body-tissue is united very 

 intimately with the testes and is difficult to remove. The photograph 

 fig. 20, shows the fat-body surrounding the testes in the form of 

 flocky masses. Here too, when examining the microtomic sections, 

 we are immediately Struck by the asymmetrical position of the testes, 

 the left one being always placed more cranially. However, I must 

 addj that this asymmetry is very variable, that is to say, sometimes 

 the testes are placed less asymmetrically with respect to each other 

 and the gut, at other times more asymmetrically and also they may 

 both be situated quite on the right of the gut. Sometimes the right 

 testis is to be found dorsally and the left ventrally of the gut. 



Two cell-layers Cover the testes. The tunica externa (fig. 23 ex) 

 is unlike those of the Diptera described hitherto, unpigmented, ex- 

 ceedingly thin and often very difficult to discover. In the tunica 

 externa, which is membraneous for the greater part, small flat nuclei 

 are sometimes to be seen. Seidom did I find a tracheal trunk in the 

 externa (fig. 22 tr), but they are very often to be seen on the outside 

 close against the externa. In fig. 23 f.h, we see the intimate connec- 

 tion of the tunica externa with the surrounding fat-body-tissue, 

 which has been only partly drawn. Cholodkovsky, who has examined 

 the testes of Leptis too, said of the tunica externa, that it is an 

 investment, rieh in tracheal trunks, and apparently composed of trans- 

 formed fat-body-cells (3, p. 394). I succeeded very rarely in dis- 

 covering sections of tracheal trunks in the externa. Neither do I 

 find any reason to affirm the supposition, that the externa may be 

 derived from transformed fat-body-cells. The interna is an epi- 

 thelium, which has developed as such over the whole lining of the 

 testes, so that there is no question of the formation of a membrana 



