LANDEK: ANATOMY OF HEMIURUS CRENATUS. 19 



At its anterior end the seminal vesicle curves ventrally, turning toward 

 the genital pore. It narrows gradually and passes by a funnel-shaped 

 termination into the ejaculatory duct (Plate 3, Fig. 28, prs.prosL,df..ej.), 

 so that it is difficult to say where one ends and the other begins. Sur- 

 rounding the narrow part of the funnel-like termination of the vesicle 

 is a muscular mass resembling that of the pharynx and consisting largely 

 of radiating fibres. It is possible that this structure is of service in 

 expelling spermatozoa during copulation, and the need of something for 

 that purpose is evident, since neither the wall of the ejaculatory duct nor 

 that of the genital sinus appears to have well-developed muscles. Be- 

 yond the funnel-shaped part of the seminal vesicle the ductus immediately 

 expands into an oval or spindle-sh-dped pars p}~ostatica (Fig. 28, prs. prost.), 

 the distal end of which joins the uterus to form the verv short common 

 genital duct. The pars prostatica thus constitutes practically all of the 

 ejaculatory duct. The narrow portion joining the uterus might possibly 

 be regarded as the ductus ejaculatorius proper. 



Surrounding the passage from the seminal vesicle to the pars prostatica 

 is a circle of cells (Figs. 28, d'.) projecting into the latter. These cells 

 are approximately conical in shape and their nuclei lie at some distance 

 from the basement membrane on which they rest. I believe that they 

 act as a valve, preventing the return into the seminal vesicle of spermatozoa 

 which have been once forced into the pars. 



Looss ('94, p. 184) describes similar cells at the opening of the vasa 

 efferentia into the seminal vesicle of Distoma tereticolle. He calls them 

 closing cells, and thinks that their function is to prevent the return of 

 spermatozoa from the vesicle into the vasa efferentia. The wall of the 

 pars prostatica shows several cells with large oval nuclei which project 

 slightly into the lumen. There also project from the wall into the lumen 

 numerous conical, or irregular, granular masses of various sizes. These 

 are probably formed by the accumulation of secretions from the cells of 

 the prostate gland at the openings of the ducts into the pars. 



Surrounding the terminal part of the seminal vesicle are numerous 

 pyriform or oval cells, which constitute the prostate gland. The lower 

 end of each cell is prolonged into a slender duct, which passes downward 

 to open into the enlargement of the ejaculatory duct referred to above 

 as the pars prostatica. The cytoplasm of these cells is rather coarsely 

 granular, and the nuclei, which are of an elongated oval- or spindle-shape, 

 are always placed transversely to the axis of the cells at about their 

 middle. 



The common genital duct, which according to Looss ('96) is to be 



