Japanese Freshwater Triclads. 13 



in tlie pharyngeal region, the ratio of the breadth ar.d length be- 

 ing 1:7-10. 



Colouration. — As is sliown in tigs. 3-6. the ground colour of 

 the body is subject to consideral)le variation according to both age 

 and individuals. In the dorsal view, fuU-gi'OAvn individuals are 

 generally of an olive-like brown colour, sometimes, but not always, 

 with dark longitudinal bands running on either side of the median 

 line from behind the eyes to the posterior parts of tlie body. Some 

 of the younger individuals are paler and the greater part of the body 

 may present various sorts of hues — not infrequently reddish, brown- 

 ish, yellowish or greenish — according to varying colourations of 

 the guts. The ventral surface is of a much paler colour than the 

 dorsal. 



Eyes. — The two crescentic eyes, each situated at the inner 

 edge of an oval colourless area, exist shghtly in front of the line 

 connecting the apices of the cephahc lappets; the distance between 

 them is shghtly less than that between either of the eyes and the 

 lateral head-margin of the same side. Besides the usual pair, one 

 or two ad\entitious eyes may sometimes 1)6 seen. The eye consists 

 of a pigment cup and numerous retina cones, as it does in the same 

 species described by Hes.se (30), Ude (79) and others. 



Auricular sense organs are, as usual, present on each side, as 

 a very distinct, slenderly reniform, non-pigmented area on the 

 cephalic lappet. 



Body Wall. — The ciliated epidermis, thickest on the dorsal 

 surface, becomes thinner as it passes round to the ventral. Lying 

 between the epidermic cells are found numerous rhabdites which 

 take place in their mother-cells embedded in the parenchyma. 

 The basement miCmbrane is an homogeneous layer immediately 

 beneath the epidermis, the cells of which are directly connected 

 with it. The underlying dermal musculature consists, as usual, of 

 three layers of circular, transverse and longitudinal muscular fibres. 

 The longitudinal muscles form a thick band just inside the trans- 

 verse layer, and are much thicker on the ventral side than on the- 

 dorsal. Besides, there is found a system of parenchyma-muscle, 

 composed of dorso- ventral fibres. Embedded in the parenchynui 



