SEA-FISHERIES LABORATORY. Jaa 
unable to demonstrate their actual endings in the tissues 
of the ctenidia. 
The posterior common pallial nerves (N.pp., fig. 31), are 
the stoutest of the nerves proceeding from the visceral 
ganglion. They leave the latter from its most posterior 
corners, and pass over the ventral surface of the adductor, 
reaching the mantle at the most lateral and posterior 
corners of the former. As they leave the muscle each 
nerve bifurcates; and the external branch, which is the 
largest, runs along the mantle edge as the external pallial 
nerve (N.p.1); the internal branch again divides, the outer 
of the two nerves so formed also runs in the muscular 
tissue of the mantle margin as the median pallial nerve 
(N.p.2); the inner one has its whole course in the thin 
tissue of the mantle within the line of insertion of the 
retractor muscles. This internal pallial nerve (N.p.3) is 
by much the most delicate of the three. 
As each common pallial nerve passes over the adductor, 
two branches are given off from its external surface. 
These enter the wall of the dorsal siphon. Three other 
nerves leave the trunk after the branch forming the 
median and internal pallial nerves is given off. These 
enter the wall of the ventral siphon. Thus the two 
siphons are innervated by five nerves on each side, of 
which two enter the dorsal, three the ventral siphon. 
Anastomoses between the first three of these siphonal 
nerves are common, and gangliform enlargements may be 
observed at their points of origin from the mantle nerve 
or further out on their course. 
The pedal ganglion (fig. 3, Pl. I., and fig. 33, Pl. VI.) is 
best exposed by removing the viscero-pedal mass, with the 
bases of the labial palps, and, therefore, the cerebral 
ganglia attached, and pinning it down in a dish with the 
anterlor margin uppermost; the muscular body-wall is 
