48 OPISTHOBRANCHIATA OF BRAZIL 



series from the upper anterior margin of the ganglion, downward 

 and backward. For the nerves originating along the outer margin 

 of the ganglion this presents no difficulties, but those nerves 

 which arise from the median portion of the ventro-anterior face 

 are of necessity more arbitrarily assigned their position in the 

 series as indicated. 



Pedal nerves. The first nerve (i), is a very slender one, 

 arising from the upper ventro-anterior face of the pedal ganglion, 

 just below and external to the entrance of the cerebro-pedal con- 

 nective, and very close to the origin of the second nerve. It 

 passes outward and forward to the integument in the eye region. 



The second nerve (2), is similar in size to the first nerve, 

 arises quite close to it, and in some specimens may possibly be 

 found to branch from a common trunk with it. It courses out- 

 ward and upward, dividing into two branches near the proximal 

 end of the penis. The dorsal one of these branches passes to the 

 dorsal retractor of the penis sheath, the ventral subdivision gives 

 off a twig which anastomoses with a branch of the third cerebral 

 nerve, another to the ventral retractor of the penis sheath, and 

 then courses forward below the penis to its distal end, giving off 

 several minute branches to it. The extreme ramifications of this 

 portion of the nerve are to the anterior end of the penis sheath 

 and to the muscles and integument surrounding it. Upon the 

 left side this nerve is distributed to the muscles and integument 

 of the body wall from the eye forward. 



In Tethys dactylomela these two nerves, numbers one and 

 two of T. cervina, are represented by but one nerve, described as 

 the first on page 27, and so figured in PI. II, p. I, but with the same 

 distribution as the first and second here described. 



The third pedal nerve (3) arises from the upper external 

 margin of the ganglion and bifurcates almost immediately. The 

 anterior one of these branches divides in turn almost at once, 

 one branch, 30,, forming an anastomosis with the first pleural 

 nerve (pi. i), being like it distributed to the dorsal peritoneum 

 and musculature back to the heart region, the other, ^b, passing 

 directly backward to a similar distribution. The posterior main 

 branch (jc) is much longer and is shown in detail in fig. 35 of 

 PI. VIII. It curves backward, sends off a branch (fig. 35, j&), to 

 the right lateral retractor muscle of the head, and to the body wall 



