90 S. GOTO. 



then runs forwards on the left side of the ovarj', then towards the right, 

 then again forwards, undergoing more or less winding!^ on the way, 

 and then towards the dorsal side of the penis, which it enters near its 

 base and, traversing it longitudinally, finally opens into its cavity 

 near or at its apex, just as in Tristomum (PI. XXVI, figs. 1, 3, 4, 

 & 6). During its course the vas deferens undergoes numerous con- 

 strictions and enlargements. 



In Microcotijle, Axine, Diclidopliom, Octocotijle, Hexacotijle, Calico- 

 tyle, Monocotijle, and Oiichocotyle I have not been able to observe the 

 vasa efferentia. In these genera, the irregular cavities of the mes- 

 enchyma between the testes probably serve as such. The single vas 

 deferens, however, can in all these genera be followed with certainty 

 up to the testes. In Calicotyle the vas deferens proceeds forwards on 

 the left side of the median portion of the body to near the pharynx, and 

 then turns backwards and towards the right and continues its course 

 into the penis. In most of the other genera above mentioned, the vas 

 deferens takes its origin from the testes more on one side of the body, 

 right or left according as the case may be, and undergoing numerous 

 windings on its course forward, opens finally into the genital atrium. 

 When the uterus and the vas deferens come to lie in the same sagittal 

 plane, the latter is always situated on the dorsal side, and opens into 

 the genital atrium also more dorsally than the former. In Axine 

 and Microcotijle the vas deferens proceeds forwards on the ventral 

 side of the ovary (Pis. I, II, & VI). 



The wall of the vas deferens consists in most species of a 

 structureless, refractive membrane of varying thickness according to 

 the species, and wholly destitute of nuclei ; but in some species there 

 is a moi'e or less distinct protoplasmic layer separated from the 

 mesenchj'ma by a basement membrane, and exhibiting at irregular 

 distances, rounded or oval, well-stained nuclei, usually containing 



