28 OPISTHOBRANCHIATA OF BRAZIL 



The second nerve {p-2), arises slightly in front of and below 

 the third, in the instance figured on the plate, passes outward 

 and gives off a branch which forms an anastomosis with the nerve 

 from the right pleural ganglion described below. The main 

 branch passes to the lateral retractor muscle of the head, a slender 

 branch also being distributed to the dorso-lateral wall. 



The third nerve (p. 3), is usually stronger, and is much 

 longer, coursing backward. It sends one branch to the muscles 

 of the dorsum, another farther on to the muscles and integument 

 of the side, a third to the Organ of Bohadsch, or hypobranchial 

 gland, and, after giving off one or two branches to the muscles of 

 the body wall, finally terminates in the right parietal ganglion, 

 thus forming a pedo-parietal connective. The branch given ofif 

 to the Organ of Bohadsch also forms an anastomosis with a re- 

 current branch from the second nerve of the left visceral gan- 

 glion, to be described farther on. 



The fourth {p. 4), is a moderate nerve in diameter but quite 

 long. It arises from the right margin of the ganglion, courses 

 backward, and is distributed to the right parapodium, like its 

 fellow of the opposite side. 



The fifth nerve {p. 5), arises close in front of the root of the 

 sixth from the median margin of the ganglion. Its strong trunk 

 soon splits into three nearly equal subdivisions, the most anterior 

 one of which is distributed to the body wall in front of the para- 

 podium, the remaining two ramifying in the parapodium itself. 



The sixth, or posterior pedal nerve, (p. 6), is, as on the left 

 side, one of the largest nerves from the ganglion. Its origin and 

 relations are similar to those of its fellow, which is also true of 

 the eighth (p.8) and tenth (p. 10), the median and anterior pedal 

 nerves respectively. In the last named there is a slight tendency 

 to variation in the number of the main branches close to the 

 ganglion, but otherwise these nerves present no great differences 

 on the two sides, nor in different individuals. 



Close to the root of the eighth nerve and a little behind it, 

 on the outer, posterior face of the ganglion is found the origin 

 of the parapedal commissure (p. p. com.). Upon the left side 

 this commissure originates from the inner ventral margin of the 

 ganglion. 



The seventh (p./), and ninth (p.p), nerves, like the cor- 



