STUDIES ON THE TURBELLARIA. 435 
subordinal name of Accela is not strictly applicable, since an 
enteric cavity, of a sort, is undoubtedly present, and though 
liable to modification, fairly constant in form and position. 
To the alternative name proposed by Mdlle. Pereyaslawzewa, 
viz. Pseudo-accela, there is the objection, which appears to 
me formidable, that its proposal was founded on the erroneous 
conception that the apparent absence of an epithelium is due 
to the action of reagents. Perhaps the term Adeloccela 
might be adopted, if the conditions obtaining in Hetero- 
cheerus should prove, on further investigation, to prevail in 
the other members of the group. 
Nervous System.—There are three pairs of longitudinal 
nerve trunks—two dorsal, viz. inner and outer, and one 
lateral. The last are much the largest and most important. 
They extend throughout the length of the body, near the 
lateral margins, and nearer the ventral than the dorsal 
surface. Irom these main lateral trunks branches are given 
off, some of which break up to form a plexus in the shape of 
a network (fig. 13), extending over the entire ventral surface 
below the muscular layers. Anteriorly the two lateral trunks 
converge, and, about midway between the dorsal and ventral 
surfaces, enter the brain. 
The two dorsal pairs of nerve-trunks unite to form, on 
each side, a common root, which is little more than a dorsally- 
directed process from the brain. 
The brain (figs. 12 and 14) is a commissure of finely- 
fibrillated material which, on its upper (dorsal) aspect, gives 
off the roots of the dorsal trunks, while on a lower plane the 
lateral trunks pass out from it. Between the roots of the 
latter is a rounded median recess, open posteriorly, in the 
brain substance. ‘This is partly covered over dorsally by 
brain substance, but is not so bounded either ventrally or 
posteriorly : it is almost completely filled by the otocyst (ot.). 
At the sides are the two small and simple eyes (e.), consisting 
merely of masses of pigment embedded in the substance of 
the ventral portion of the brain, which, owing to the presence 
of the otocyst recess, is divided into two lobes, each giving 
