1918.] ToKio Kabueaki : Triclads of the InU Lake. 189 



one another to form somewhat wider ducts, and then take a course 

 directed towards either of the vasa deferentia, which are distinctly 

 discernible in the pharyngeal region. The vasa deferentia, proceeding 

 backward inside the longitudinal nerve cords on the ventral side, rise 

 upward to enter the penis-bulb separately on the sides and finally 

 open into the lumen of the penis or the ejaculatory duct (see figs. 4 and 

 5). The vas deferens, which is filled with spermatozoa, has the wall 

 consisting of an epithelium and an outer layer of ring-muscle fibres 

 best developed in the neighbourhood of the penis. 



The penis consists as usual of two parts, viz., the free, conical and 

 massive intromittent part lying horizontally in the penis-sheath, and 

 the bulbous basal part of strongly muscular nature. The latter pari: 

 encloses a wide and smooth-walled cavity of a spheroidal shape, the 

 seminal vesicle ; posteriorly this is continuous with the ejaculatory duct, 

 which opens into the penis-sheath at the under side of the tip of the 

 penis. In its course the ejaculatory duct makes an obliquely anteriorly 

 directed annular outbulging, much as in PI. gonocephala ; consequently 

 there is formed in the lumen a small backwardly directed process 

 surrounded by the said outbulging and which is axially traversed by 

 the narrow anterior section of the ejaculatory duct. It is a short 

 distance in front of the above process that the duct receives laterally 

 the outer ends of the vasa deferentia. Imbedded in the parenchyma 

 around the penis-bulb are numerous eosinophil penis-glands, the ducts 

 of which enter the penis at the base and open into the ejaculatory duct 

 behind the outbulging mentioned above. 



The paired ovary is situated far behind the brain and between the 

 fourth and fifth anterior lateral branches of the gut. It is of a nearly 

 spherical shape. 



The vitelline glands are represented by cellular cords with the cells 

 arranged in one or more rows ; they are very extensively distri- 

 buted posteriorly from the region of the ovaries and in the interstices 

 between gut diverticula, and stand at many points in connection with 

 the oviduct. 



The oviduct of each side starts from the antero-laterai aspect of the 

 ovary as an ampuLlaceous passage filled with spermatozoa ; this soon 

 assumes the character of a narrow tube, which proceeds straight back- 

 wards just along the outside of the nerve-cord. In the region of the 

 genital aperture, the oviduct rather abruptly bends mediad, at the same 

 time rising slightly upward, soon to open into the vestibulum from be- 

 hind near the outer end of the vaginal canal, without uniting with its 

 fellow of the opposite side into a common duct. The oviduct shows a 

 distinct lumen in its entire length. Its actual wall is formed by a homo- 

 geneous and ciliated layer which shows no nuclei ; — apparently a part of 

 an epithelium, of which the nucleus-containing parts are sunk into the 

 surrounding parenchyma, as has been observed by several investigators 

 to be the case in PI. gonocephala, PI. polychroa, Dendrocoelum lacteum, 

 etc. Directly external to the layer mentioned are the two layers of 

 internal circular and external longitudinal muscular fibres. An inver- 

 sion in the relative position of these two muscular layers does not occur 

 in the terminal parts of the oviduct, as it does in some species according 



