332 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. 



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, 

 c 5a. This corresponds to a part of the fifth cerebral nerve, its remaining por- 

 tion, c 5h, being included in the same connective-sheath as c 2, though with an 

 entirely separate origin. The nerve c 5a passes shghtly 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 c 5a 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 



