Japanese Freshwater Triclads. 



29 



vitelline glands are comparatively large and of an irregular contour, 

 due to mutual compression. They are found to contain numerous 

 strongly refractive granules. 



The oviduct of each side starts from the postoro-lateral aspect 

 of the ovary as a funnel-like widening, which is hned with a 

 single layer of columnar cells as has deen shown by Matttesen (52) 

 to be the case in I)endr. lacteum. This soon assumes the character 

 of a narrow duct which proceeds backwards just along the outer 

 side of the longitudinal nerve cord. In the region of the penis it 

 nears the median line, slightly ri>ing upwards at the same time, 

 and finally unites with its mate of the opposite side into a common 

 duct before opening into the ati'ium between the penis-sheath 

 and the vestibulum from above. The oviduct exhibits a distinct 

 lumen throughout its entire length, and is found filled up with 

 spermatozoa. As in Bd. annandalel, Bd. brunnea and PI. yono- 

 cephcda. its direct wall is an homogeneous and ciliated layer showing 

 no nuclei at all. The nucleus-containing parts are sunk into the 

 surrounding parenchyma beneath the two layers of internal circular 

 and external longitudinal muscular fibres which come directly 

 external to the layer mentioned above. The single duct is sup- 

 plied with numerous unicellular glands. 



The seminal receptacle is a very large sack-like organ wnich 

 is of an irregular shape and is placed in front of the penis. In 

 structural respects its wall presents no novel feature, and it is an 

 epitheleum made up of large columnar cells of a glandular nature, 

 outside which is a thin muscular layer. In some specimens I 

 have examined, the organ seems to have been in secretory ac- 

 tivity, the cells being vacuolated. On some occasions the organ 

 is found to contain one or two well-formed and empty spermato- 

 phores of a pyriform shape, enveloped in a coagulum of the 

 secretion. 



The receptacle gives rise behind to the wide vagina, which 

 proceeds backwards dorsal to the penis and dips down to open into 

 the vestibulum. In the middle of its course the duct is gently 

 constricted, as is seen in text fig. 9. The lining epithehum is 

 made up of cells of an elongate-pyriform shape, resting on a base- 



