504 P- E. Keuchenius, 



pregnation with colour happened very slowly, so that 1, 2 or 3 days, 

 and with larger objects even 4 days were wanted. As for maceration 

 for which I also feared at tlie beginning, there was none. Besides 

 I kept the objects 24 hours in the other liqiiids through whicb they 

 had to pass. Finally they were imbedded in hard paraffin, which was 

 necessary for the sectioning of the hard, and somewhile even very 

 hard chitin. To get series that should be really good, I dripped a thin 

 layer of soft paraffin on two opposite sides of the blocks to be sec- 

 tioned. My sections were all of a thickness of TVgmicron. 



Anatomical Part. 



Farn. Syrphidae. 



Eristalis arhustorum Linn. (Fig. 1 — 7). 



The male genitalia are composed of a pair of testes with their 

 vasa deferentia^ one pair of accessorial glands, vesicula semi- 

 nalis, ductus ejaculatorius and sacculus ejaculatorius (fig. 1). 



On examining the microtomical sections, it becomes evident at 

 once, that both testes in relation to each other occupy an asvin- 

 metrical position, which, however, is not to be observed in the gonads 

 which are sectioned out of the abdomen. Also one can see a strong 

 asymmetry in the caudal end of the abdomen, The fact is that this 

 end is bent to the right (fig. 2). I will come back to this phenomenon, 

 which I have also met with in other species of the Syrphidae, in 

 my final conclusions. As regards the Situation of the testes in the 

 abdomen, we observe that the right testis is always placed more 

 cranially than the left one. 



The testes are light brown coloured bodies, which are pointed 

 both cranially and caudally. They are surrounded by two layers, of 

 which I would call the outside one, the tunica externa (or »peri- 

 toneal Hülle") and the inside one, the tunica interna s. propria. 

 The externa is a thin layer (fig. 3 ex), in which here and there are 

 to be found very large nuclei (fig. 3 n) and which is coloured by light 

 brown pigment-granules. Also I have seen several times sections of 

 tracheal trunks in the externa as well outside very closely against 

 it (fig. 3tr). Of a connection of the tunica externa with the fat- 

 body-tissue, there is no question, so that the testes lie free in the 

 abdomen. The tunica externa is composed distally, in the direction 

 of the vas deferens, of epithehum, in which nuclei are clearly to 

 be Seen. Cranially, towards the blind end of the testes, the epithe- 

 hum loses little by little its cellular nature and continues in a mem- 



