The structure of tlie internal Genitalia of some male Diptera. 505 



braneous lining, the membrana propria, in which no nuclei are 

 to be observed. The Contents of the testes consist of (fig. 3): (I 

 avail myself liere of the nomenclature used by Munson (13) in 1907) 

 gonocysts containing spermatogones, cytocysts containing sper- 

 matocytes, spermatocysts containing spermatids and sper- 

 matozoa, and also bundles of ripe spermatozoa. In the testes 

 are thus to be found, with the exception of the apical-cell, several, ■ 

 stages of the development of the male germ-cells. In many of these 

 Clements I observed vigorous mitotical nucleus-divisions. I must 

 however add, that on going from the blind apex to the opening of 

 the testes in the vas deferens, one always meets a progressive 

 series of everolder stages of the ontogeny of the spermatozoa, so that 

 in the vicinity of the vas deferens only ripe spermatozoa are 

 present. Besides these different elements, there are to be found in 

 the distal part of the testes round cellular bodies (fig. 4 ?/) and some 

 vacuolar cavities, of which the origin is not clear to me. The round 

 cellular bodies however, I think to be derived from degenerated gono- 

 or cytocysts. It Stands to reason, that the signification and origin 

 of those elements is only to be made out Avith certainty by a thorough 

 investigation of the ontogenie of the testes and their Contents. In 

 the distal part of the testes I saw fine tissue-septa on some places 

 going out from the epithelium and pushing into the lumen of the 

 testes. 



Bothinvestments of the testes continue on the vasa deferentia, 

 which thus are also formed by a tunica externa and interna. The 

 brown pigmentation of the tunica externa however, only continues 

 a short distance on the vas deferens and stops then, so that the 

 nuclei of this cell-layer comes more to the front. 



The accessorial glands are two twisted tubes. Also these two 

 gland-tubes consist of two cell-layers (fig. 7). The tunica externa 

 (fig. 7 ex) is only a very thin cell-layer with flat nuclei. The interna 

 is a high columnar epithelium, of which the round nuclei are entirely 

 situated at the base. The cells are of different heights, in consequence 

 of which the lumen of the tubes is irregulär and does not agree with 

 the outline of the gland. In some cells when in function perhaps, 

 I saw very often small vacuoles (fig. 7 vac), whilst on several places a 

 seemed edge was to be seen, formed by the expelled secreta. The 

 gland-cells are nearly all separated by very distinctive intercellular 

 fissures, which are probably caused by shrinking during fixation. These 

 intercellular fissures are indeed pretty frequent in gland-epithelium. 



