302 THE DOLABELLINAE. 
two branches, c 2a, terminates at the base of the anterior tentacle in a small — 
rounded ganglion, from which numerous delicate nerves ramify to the tentacle 
itself. The lower ramus, c 2b, passes forward, gives off a delicate branch to . 
the lateral protractor muscles of the pharyngeal bulb, and is distributed to the 
integument of the mouth-region. 1 
Immediately above the origin of the second cerebral nerve on the right 
side, but above the first cerebral nerve on the opposite one, arises a strong trunk, 
c5a. This corresponds to a part of the fifth cerebral nerve, its remaining por- 
tion, c 5b, being included in the same connective-sheath as c 2, though with an > 
entirely separate origin. The nerve ca passes slightly outward, and then 
straight forward over the pharyngeal bulb, bifurcating after a short course. 
The more dorsal of its rami, on the right side, gives off a delicate branch at the — 
posterior border of the dorsal rectractor of the penis, which courses forward 
and ramifies to the body-wall just below the anterior end of the penis-sheath. 
A second small branch forms an anastomosis with the twig from the first cere- 
bral nerve (possibly, however, coming from the third pedal nerve through the 
anastomosis of those two previously described, instead) and is distributed 
to the dorsal protractor muscle of the penis-sheath. The main portion of the 
dorsal ramus branches to the penis-sheath and to the integument at the side of 
the mouth. The more ventral ramus of ¢ 45a passes directly forward to the 
integument of the lateral mouth-region. . 
The remaining portion of the fifth cerebral nerve, c 5b, might be considered — 
as a separate part of the second cerebral nerve with equal justification. It is 
united in the same connective-tissue sheath as the latter, accompanies it in 
the first part of its course, and is distributed to the integument and muscles — 
of the ventro-anterior insertion of the pharyngeal bulb in the body-wall. This — 
distribution resembles that of the fifth cerebral more than that of the second, 
which is to the dorsal and dorso-lateral portion of the pharyngeal bulb insertion. 
Its point of emergence from the cerebral ganglion surface is entirely separate 
from that of either the second or the fifth nerves, being nearer the fifth on the © 
right side and nearer the second on the left. 
From the dorso-lateral surface of the cerebral ganglia, just above the origin 
of the cerebro-buccal connectives, the slender fourth cerebral, or optic nerve, 
c 4, arises. On the right side it crosses obliquely forward over the base of the 
fifth cerebral nerve and passes outward, inclosed in the same connective-tissue 
sheath with it along its inner border, for a short distance, before taking up an 
independent course. Upon the left side the optic nerve does not cross the base 
