26 
tion dietated by the central position which Proneomenia appears to 
occupy with respect to its nervous system amongst the different 
genera. It moreover appears to me that any such suggestion would 
be more acceptable if Proneomenia were eventually found to be in 
the possession of a posterior commissure between the lateral nerves, 
which as yet I have not succeeded in demonstrating with certainty. 
THE DIGESTIVE SYSTEM. 
The digestive tract of Proneomenia occupies the greater part of 
the available space inside the bodywall. Its anterior and posterior 
openings were noticed above: both situated ventrally, the one at 
the thicker, the other at the thinner extremity of the body. It has 
moreover already been mentioned that the mouth is not continuous 
with the ventral furrow, but separated from it by a narrow bridge 
of intervening cutaneous tissue (fig. 3). According to TULLBERG 
(31, fig. 2) and v. GrAFF (6, p. 559) a similar discontinuity is present 
in Neomenia. v. GRAFF moreover notices that another bridge of the 
spiculated epiderm separates the anus from the ventral groove. I 
could convince myself by the aid of Prof. von GRAFF’s prepara- 
tions that this statement is due to an optical illusion and that in 
his specimens of Neomenia as well as in those of TULLBERG the 
fact holds good which I again found confirmed in Prof. LAnkESs- 
TER’S sections and in my own preparations of Proneomenia viz. 
that the ciliated ventral groove merges directly into the anal cavity 
(fig. 4, 13 and 34). How this optical allusion was brought about 
has already been noticed in a preceding chapter (p. 12). 
Three divisions may be separately noticed in the digestive tract 
of Proneomenia, in many respects corresponding with the similar 
arrangement noticed by former observers in Neomenia. These divi- 
sions are: the buccal mass, the ceiliated intestine and the reetum. 
Of these divisions the first is eminently muscular, the second not 
at all so, the third only in a slight degree. 
The muscular pharynx into which the mouth opens is attached 
to the bodywall (from which it is separated by a not inconsiderable 
