SEA-FISHERIES LABORATORY. 415 
there are collections of nerve cells along certain nerves, 
ie particular the circumpallial nerve (fig. 26, NV.c.), 
which renders the latter almost a fourth ganglion, both 
structurally and functionally. 
Cerebral gangha The pair of ganglia known as the 
cerebral, or better —the cerebro-pleural, representing the 
fused cerebral and pleural ganglia occurring in Nucula 
and Solenomya, are found best by pulling the lower lip 
dorsally and moving the labial palps aside, so as to lay 
bare the area between the lower lip and the foot. The 
ganglia will then be seen faintly through the overlying 
tissue, which must be removed carefully or they will be 
pulled away with it. They are situated a considerable 
distance below the mouth and oesophagus, and very close 
to the pedal gangha. Nach ganglion (fig. 27, G. cb.) 
shows indications of being bilobed, and this is further 
borne out by sections which show a distinct, though not a 
deep, division into two lobes. From the upper corner 
arises the cerebral commissure (figs. 26 and 27, Com.). 
This connects the two ganglia and passes dorsally over 
the oesophagus, but owing to the position of the cerebro- 
pedal ganglia it is a larger loop than is usually the case. 
From the outer sides of the ganglia, just below the 
depression dividing them, arise the anterior pallial nerves 
(figs. 27 and 26, NV. pa.), and a smaller nerve which gives 
branches to the labial palps (fig. 27, WV. .). 
The Anterior Pallial Nerve les close to the cerebral 
commissure, and passes with it to the side of the 
oesophagus, embedded in the digestive gland. It rises to 
the surface and enters the mantle just dorsal to the upper 
lip where this joins the outer labial palp on each side, 
then, dividing into two branches, it passes to the margin 
of the mantle and joins the circumpallial nerve (fig. 2A, 
N.c.) by several branches. 
