Japanese Freshwater Triclads. ]^5 



■sure?^. Lateral nerves are sent uiit from tlie trunks usually at points 

 opposite to the union of the latter with transverse commissures. 



Genital Organs. — The common genital aperture exists slightly 

 in front of the middle of the posterior third of the hody. It leads 

 directly into the simple penis-sheath, much as in PI. polychroa. 



Numei'ous follicular testes are placed close together in the 

 dorsal parts of the body, arranged in two longitudinal lateral zones 

 wdiich extend from behind the ovaries to nearly the posterior end 

 ■of the body. 



The vasa deferentia, filled with spermatozoa, are distinctly 

 •discernible in the pharyngeal region. After running Ijackwards 

 just along the inner side of the longitudinal nerve cords on the 

 ventral side, they rise obliquely upwards to open separately into 

 the lumen of the penis, at the lateral sides of the bulbous part. 



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

 massive intromittent part lying nearly horizontal in the penis- 

 sheath, and the semispherical bulbous part of strongly muscular 

 nature. The latter part encloses a moderately wide and more or 

 less folded cavity, the seminal vesicle; posteriorly this is continuous 

 with the slender ejaculatory duct, which opens into the penis-sheath 

 on the under side of the penis, not at the ti}). In its course, the 

 ejaculatory duct shows an oblique, anteriorly directed annular 

 outbulging, as in PL burmaensis Kab; it consequently brings al;)OUt 

 a small, conical posteriorly directed process which is surrounded l)y 

 the said outbulging, and which is axially traversed by the nariow 

 anterior section of the ejacultory duct. 



The paired ovary occupies a ventral position between the 

 second and third lateral branches of the anterior trunk of the 

 intestine. It is a spherical mass of egg-cells in several stages of 

 development and is enveloped by the tunica propria. 



The vitelline glands are represented l)y cellular cords with 

 ■cells arranged in two or more rows; they are very extensively 

 distributed posteriorly from the region of the ovaries and in the 

 interspaces between the gut diverticulae, and stand at many points 

 in connexion with the oviduct by means of a spherical or pyriform 

 giant cell. 



