Notes on the Central Nervous System of 
a Free-Living Marine Nematode 
WILLIAM A. HILTON 
The species studied was the one which is most abundant at Laguna Beach among 
Alge and in sand at low tide. It corresponds closely to Enoplus brevis Duj. 
The nervous system has several features not described in related forms. There is 
a concentration of the central nervous system. There is a single large ganglion or 
brain in the snout above the mouth, from this two connectives pass ventrally to join 
the broad ventral nerve band in the mid-ventral line, while the only other longitudinal 
nerve noted was the very small mid-dorsal. Lateral nerves were not found. 
The head or snout ganglion is provided with three eye spots, and unpaired dorso- 
median and a pair of latero-ventral ones. The sensitive region is so placed as to 
receive stimuli from above by the median eye and from below by the lateral eyes. 
The eyes are little more than concave pigment spots imbedded in the mass of the 
ganglion. A number of fibers pass from the ganglion forward to supply the thick 
sensory epithelium of the tip of the snout. 
The ganglion is rather complex in structure. It has a central and somewhat 
ventral mass of fibers surrounded on all sides by nerve cells and fibers mingled. There 
are two centers composed each of cell areas surrounding a fibrous mass; these seem to 
be associated with fibers connected with the sensory epithelium of the snout and they 
resemble slightly the olfactory areas of certain invertebrate brains. 
The dorsal nerve trunk is not cellular. The ventral nerve trunk is thick and 
broad. Ventrally it is nearly fused with the underlying cells of the body-wall, while 
dorsally it is bounded by a closely applied muscular layer. The nervous tissue itself 
is traversed by heavy lines which in part may be merely supportive in function, the 
lighter strands, both transverse and longitudinal, are branches from the rather abun- 
dant cells which are for the most part located ventrally. 
(Contribution from the Zoological Laboratory of Pomona College.) 
