Japanese Freshwater Triolads. 33 



a slight neck-like naiTowiiig. The trunk is slender and for the 

 most part of a nearly uniform breadth, though it tapers behind to 

 a bluntly pointed end. Tlie worm sometimes reaches 17 mm. in 

 lenght and 2 mm. in breadth at the pharyngeal region, but is 

 generally smaller, the breadth and length being in the proportion 

 of 1 to 6-8. 



Colouration. — The greater part of the bod}^ may present various 

 hues — not infrequently light salmon, light brownish, dark or red- 

 dish var3nng from pink to blood-red or chestnut-red according to 

 varying colouration of the intestine. The head and the body- 

 margin are nearly culuurless and translucent. The pharjnix and 

 genital organs may be discerned on the dorsal side in a white 

 colour. 



Eyes. — The extremely small eye-spots occur in abundance, 

 increasing in number with the growth of the bod3% but never quite 

 reaching 100 in total number. They are distributed in two longi- 

 tudinal zones which converge and meet in front and thus form a 

 horse-shoe-shaped tract, situated a considerable distance apai't from 

 the head-margin both anteriorly and laterally. Posteriorly the 

 tract extends to about the third pair of the gut branches of the 

 anterior trunk. 



The eye consists simply of a small pigmented cup, partly 

 tilled with a iDeculiar cellular substance, whose true nature could 

 not be ascertained from any of the sections. 



Body Wall. — The epidermis is not of the same thickness all 

 over the body, being much thicker on the dorsal than on the 

 ventral side. As is well known, it is made uj3 of closely- packed 

 ciliated columnar or cuboidal cells resting upon a tine basement 

 membrane, each with an oval nucleus at its base. The protoplasm 

 of the cells is generally fibrillated, the course of the tibiillae being 

 in a general way perpendicular to the surface. In tlie anterior 

 region the epidermis comprises some 12 special sensory cells, which 

 are situated between the general cells and provided with well- 

 developed cilia. The sensory cell is of a spherical or ovoidal shape 

 and is sunk into the surrounding tissue. Where the cilia are 

 inserted in the cell, there exists a deeply staining, finely granular 



