8 ARKIV FÖR ZOOLOGI. BAND Ii. N:0 13. 



is provided with a thick muscular sheath. The passage be- 

 tween the two sacs is very short. The true seminal vesicle 

 in its turn opens by means of a short duct in the back end 

 of another larger vesicle, the bulb-Iike prostatic vesicle. The 

 lumen of this muscular vesicle receives the granular secretion 

 of the glandular epithelium and the outlying glands, the 

 ductuli of which traverse the thick muscular coat of the 

 vesicle. The prostatic vesicle has not a strict longitudinal 

 course but is directed somewhat ventrally. At its anterior 

 end it tapers to a short ejaculatory duct which opens at the 

 apex of a thick conical penis. This penis, which is directed 

 forward, has a feeble muscularis and a well developed pa- 

 renchyma which encloses the prostatic vesicle. It is unarmed 

 and provided with a thin penial fold (= »Penisscheide»). 

 The penis nearly fills up the whole antrum masculinum, 

 which is thus reduced to a fissure-like space of greater length. 

 The antrum is separated from the pharyngeal sac by an 

 exceedingly thin wall and opens to the exteriör closely behind 

 the mouth, the distance being only y^b mm. In this close 

 approach of the male porus to the mouth we have a re- 

 semblance to another cotylean genus, Stylostomum^ where 

 there is a common opening. The incongruity of the male 

 apparatus prevents us from attaching any phylogenetic im- 

 portance to this feature, especially as the other sexual organs 

 and the pharynx are also dissimilar. The text figure 3 shows 

 the arrangement of the male copulatory apparatus. 



The ovaries are only few but they are so much the 

 larger. They do not occupy any extreme dorsal position 

 which is so common among the polyclads. On account of 

 the extremely large size of the ova, of which every ovary 

 contains only one larger, maturing egg at the same time, 

 the ventral ends of the ovaries often reach the ventral mus- 

 cular body-wall, forcing out of place the testes or, as it 

 sometimes happens, flattening them out considerably. This 

 preponderance of the ovaries at the expense of the testes is 

 easy to understand, but I have never met with it before in 

 the polyclads, where the male and female reproductive organs 

 are usually restricted to different regions of the body. 



The germinative zone of each ovary is variably placed: 

 dorsally, ventrally and laterally, and contains only a few 

 small cells. The largest of these young ovarial cells of the 



