26 OPISTHOBRANCHIATA OF BRAZIL 



the whole band. From the ventro-posterior margin of each pedal 

 ganglion a much more slender parapedal commissure (p. p. com.) 

 arises. It is 7.0 mm. in length, being more than double that of the 

 thicker pedal commissure, and describes a posteriorly directed 

 loop below the esophagus. Somewhat to the left of its middle 

 point a long slender unpaired nerve (a) is given off, in one case 

 being formed by a union of a short branch from each side of the 

 loop, in others coming from the left side alone. It passes back- 

 ward and is distributed to the pedal artery and foot. 



From the pedal ganglia arise ten pairs of nerves, which show 

 such differences in the two sides that they are here described 

 separately. 



Left pedal nerves. The first nerve (p.i), is quite slender. 

 It arises from the upper outer border of the ganglion and passes 

 backward and is distributed to the peritoneum and muscles of the 

 posterior dorsum. 



The second nerve (p. 2), arises close below the first and is 

 of similar size. It bifurcates close to the ganglion, one of the 

 rami thus formed passing backward to a similar distribution 

 as that of the first nerve ; the other ramus divides into (a) a branch 

 curving forward and forming an anastomosis with a branch of 

 the second pleural nerve, described below, and {h) a second 

 branch which is distributed to the muscles of the dorso-lateral 

 region. 



The third {p. 3), is a rather slender nerve arising just below 

 the first and second, and more upon the anterior face of the gan- 

 glion. In one instance it appeared as two nerves very close 

 together. It branches to the integument and muscles of the dorsal 

 wall above the pharyngeal bulb, one branch passing undivided to 

 the region of the eye. 



The fourth nerve (p. 4), arises from the lateral margin of 

 the ganglion, is rather long and strong, passing backward to its 

 distribution in the anterior portion of the parapodium. 



The fifth {p. 5), is a strong nerve from the mid-lateral margin 

 of the ganglion. It soon divides into three branches, the anterior 

 one of which passes to the muscles of the body wall, the other 

 two to the parapodium. 



The sixth nerve (p. 6), is the largest of the pedal group. It 

 arises close to the root of the fifth, and from its distribution is 



