TETHYS DACTYLOMELA (RANG) 2"] 



termed the posterior pedal nerve. It soon divides into two main 

 branches of unequal size, which pass backward and ramify to 

 the posterior portion of the foot, giving off a few slender branches 

 to the mid-lateral region of the same. 



From the ventro-anterior face of the ganglion, near the 

 entrance of the cerebro-pedal connectives arises a very slender 

 nerve, the seventh (/>./). A short distance below it, and from the 

 same face, the ninth nerve (p.p), is also given off. These two 

 nerves are closely enmeshed in the capsule of connective tissue 

 enveloping the posterior end of the pharyngeal bulb, and may be 

 easily overlooked. A short distance from their origin they are 

 connected by an anastomosis, and beyond this the two have a 

 similar distribution, branching richly to the peritoneum, the aorta, 

 and the muscles of the dorso-lateral wall of the body. 



The eighth, or median pedal nerve, (p.8), arises at the outer 

 lower margin of the ganglion, passes outward and backward, 

 dividing into two nearly equal rami, which are distributed to the 

 median region of the foot. 



The tenth, or anterior pedal nerve (p.io), is the lowermost 

 one of the series. It is of about equal caliber to the eighth, and 

 divides into three main branches which curve forward to the 

 anterior portion of the foot. 



Right pedal nerves. The first pedal nerve (p.i), arises as 

 a slender process from the outer upper margin of the ganglion, 

 and soon divides into two unequal branches. The larger of these 

 passes directly to the muscles of the lateral wall. The other 

 branch subdivides again, in a short distance, into an anterior and 

 a posterior branch. The posterior one of these innervates the 

 penis, the anterior one runs parallel to the latter organ, gives off 

 two or more delicate twigs to it, which anastomose with the sub- 

 divisions of the posterior branch, the main trunk terminating in 

 the muscles of the mouth region on the right side. 



The second and third nerves are closely associated at their 

 origin, some individuals showing them as separate nerves, while 

 others show the two united as a single nerve for a very short 

 distance. In fig. 8 of PI. II I have shown the separate condition. 

 In Tethys cervina, as will be seen, the united condition was 

 found, and further comment will be made in the description of 

 the central nervous system of that form. 



