238 F. W. GAMBLE, B.SC. 



Length 12 — 25 mm. Body delicate, of variable shape, more or less 

 elongate, broader in front than behind, the anterior margin semicircular; 

 young specimens, as Dalyell has remarked, have the outline of a 

 spherical triangle. The colour, if present, is brown ; it is, however, 

 extremely variable in amount and intensity : it is due partly to 

 parenchymatous pigment, partly to the gut branches. In the middle 

 line, not far from the hinder end, are two white areas ; the foremost 

 represents the male copulatory organ, the one behind it the " shell- 

 gland." Between these and the brain a brown median area, surrounded 

 by a clear whitish space, represents the main-gut and the uterus outside 

 it. A V-shaped spot leading to the male pore is due to the underlying 

 vasa deferentia. The ovaries appear (especially on a black ground) as 

 white dots. From the white ventral surface the plaited pharynx and 

 genital organs may be seen. Active swimming movements are pro- 

 duced by the expanded edges of the anterior end of the body. 

 Between the male and female genital apertures is a depression, the 

 lips of which are strongly muscular,, and constitute a "sucker." The 

 mouth is in front of the centre. It leads into the strongly puckered 

 pharynx lying in its sheath. From this the main-gut arises, and runs 

 forwards towards the brain, and backwards to the commencement 

 of the posterior third, giving off as it does so the numerous lateral 

 branches, which in turn subdivide and end in fine cseca along the 

 margin. The brain is distinctly bilobed. The lobes are oval, their 

 long axes parallel to one another and to that of the body. Five 

 anterior pairs of nerves supply the region in front and at the sides of 

 the brain, and two lateral ones the rest of the body. The eyes vary in 

 number and arrangement. In front of the brain are usually two 

 distinct patches of loosely arranged eyes at the bases of the nerves 

 (corresponding to the eyes at the bases of the tentacles in 

 Planoceridee). Opposite the bases of the fifth pair of nerves is a 

 compact group of larger, chiefly reniform eyes. In some specimens, 

 however, the tentacular and cephalic groups of each side are continuous 

 with one another. The genital apertures have already been noticed. 

 From the numerous scattered testes, vasa efferentia arise. These 

 gradually unite to form the pair of vasa deferentia which run at the 

 sides of the pharynx, and before uniting at the base of the penis give 

 off a posterior branch, which joins the one of the other side behind 



