NILS HJ. ODHNER, PTISANULA LIMN^OIDES. 7 



behind the oesophagus, vvhere it is widened and furnished 

 with a coecal appendage, running forwards and upwards. 

 Further back the canal grows narrower and terminates blindly 

 (Figs. 5 and 9). 



Within this canal or sheath the penis projects like a 

 small bud from the walls, which at this point are strongly 

 muscular. Before the glans penis, i. e. in the front part of 

 the sheath, the walls are furnished with strong circular folds 

 projecting into the lumen; towards the aperture the sheath 

 widens sufficiently to cover the upper and right side of the 

 pharynx. Behind the glans a ciliated epithelium lines the 

 walls; further on it gives place to large bladder-like cells in 

 irregular order, evidently with secretary function. 



In Diaphana similar features prevail on the whole, though 

 the sheath of the penis is longer and more winding and the 

 glans is also more perfected (Fig. 10). In the distal part the 

 sheath grows narrower and the walls become muscular and 

 the canal very fine ; this widens and opens to a f urrow, from 

 the bottom of which a rigid projection rises (Fig. 10), point- 

 ing forwards and consisting of a fibrous central pillar clothed 

 with a simple layer of small ectoderm cells. The male orifice 

 in Diaphana is situated near to the mouth on the right side. 

 From it leads a ciliated seminal groove backwards under the 

 cephalic lobe and över the neck to the female orifice. This 

 is simple with a tendency to fall into two pores, of which 

 one leads into a canal combined with a glandular dilatation 

 along its outer side (Fig. 11), the other belongs to a narrower, 

 complexly winding duct, lined with a folded ciliated epithel- 

 ium and communicating at many points with the canal just 

 named ; in its upper part the last duct exhibits a sac-f ormed 

 dilatation. This last-named canal is probabJy a rudimentary 

 male outlet of the hermaphrodite duct. The second canal 

 is the oviduct with its albumen gland. The connections 

 between them reminds one of the conditions found in the 

 Nudibranchia. At their upper ends the female and the male 

 ducts join and pass into a glandular hermaphrodite canal, 

 which issues from the hermaphrodite gland. 



As regards Ptisanula, an outer seminal groove is likewise 

 present at the right side of the body, but the other parts 

 of the genital apparatus seem to be simpler than in Diaphana. 

 One duct only, as far as can be stated, leads from the female 



