Japanese Freshwater Triciads. 49 



The two ovarief^ are placed each ventrally in front of the first 

 pair of tlie gut brandies. (^wing to my careless manipulation 

 while preparing the material, the course of the oviducts could not 

 l)e distinctly traced from any of the sections available. A short 

 stretch of longitudinal canal, i'unniiig along the ventral side of 

 the atrium and joining this at a point about midway between the 

 tip of the penis and the junction of the vagina with the atrium, 

 l^robably represents the unpaired terminal part of the united 

 oviducts. The seminal receptacle is a slender tubular canal, run- 

 ning over the penis and extending a short distance beyond this 

 anteriorly, much as in Poll/, ijlmai. Its direct wall is an epithelium 

 made up of columnar cells of a glandular nature, surrounded by a 

 thin muscular layer. The vaginal canal dips below to open into 

 the atrial passage from above. 



Habits. 



Occurrence. — The freshwater Triciads inhabiting both running 

 and standing waters are found, for the most part, clinging to the 

 under side of stones or other sunken objects, which project up from 

 the bottom or out into the water, or which lie against each other 

 so that the under side is not buried. The stones are more or less 

 rough, covered with tiny crevices which make good hiding places, 

 the worm being almost below the surface and thoroughly protected 

 but still able to make use of the swift current of fresh water. PI. 

 gonocephala, which is of wide distribution in the northern hemi- 

 sphere, is very abundant in l)0tli standing and running waters, being 

 widely distributed from the mountainous region nearly down to 

 the sea level. PI. rlvkla, PL pelluclda- Poly, harafto and Poly. 

 À/mai usually inhabit cool running streams, the middle two species 

 being not infrequently found together. Poly- miriculatd. though 

 sometimes occurring in stagnant w\ater, abounds in cold streams. 

 Bd. anîiandalel occurs on the muddy bottom of the lake, whereas 

 its ally, Pd. brunnea, distinguished by the small size of the body, 

 is usually found in running water. PI. papUllfera is known as 



