TETHYS DACTYLOMELA (RANG) 29 



responding nerves of the left side, arise from the ventro-anterior 

 face of the ganglion, and present some difficulty as to their exact 

 numerical order with respect to the other nerves of the same gan- 

 glion. They are also closely bound up in the connective tissue 

 sheath surrounding the end of the pharyngeal bulb. The seventh 

 nerve is slightly larger than the ninth, and is distributed mainly 

 to the penis, and the body wall in the immediate neighborhood of 

 that organ. It also forms a strong anastomosis with a branch 

 of the ninth, as is shown in the fig. 8 of PI. II. The ninth nerve 

 is distributed mainly to the muscles of the body wall below the 

 lateral retractor of the head. 



Pleural ganglia. The pleural ganglia (pi. g), the "proto- 

 visceral ganglia" of Mazzarelli ('93), are quite small, i.o mm. 

 in diameter, and nearly spherical. They are situated upon the 

 upper posterior face of the pedal ganglia, and are connected 

 with them by the extremely short pleuro-pedal connectives. From 

 the posterior surface of the left pleural ganglion arises the long 

 and strong pleuro- visceral connective (pi. v. con.), while from a 

 nearly similar position upon the pleural ganglion of the right 

 side is given off the pleuro-parietal connective (pi. par. con.), 

 nearly equal in length. These two connectives pass directly back- 

 ward, converging to terminate in a pair of ganglia, the parieto- 

 visceral ganglia, lying on the inner surface of the dorsal body 

 wall at a point midway between the anterior bases of the pleuro- 

 podia and" close to the anterior insertion of the mantle. 



The pleural ganglia are usually described, e. g. by Mazza- 

 relli ('93, p. 1 08), as not giving off any nerves in the Aplysiidae. 

 But in Aplysiella petalifera Rang Pelseneer ('94) describes a 

 lateral nerve arising from each pleural ganglion and forming an 

 anastomosis with a pedal nerve of the same side, which condition, 

 he further states, also exists in certain species of Aplysia and the 

 Gymnosomata. Vayssiere ('85) describes and figures a nerve 

 from each lateral visceral (pleural) ganglion in Notarchus 

 punctatus Philippi, which is associated in a part of its course 

 with a pedal nerve to the mantle, and is distributed to the lateral 

 tissues of the body on the right side, at the base of the branchia. 

 Whether an anastomosis of these two nerves occurs or not does 

 not appear from his description. In the two species of Aplysiidae 

 from Brazil unmistakable though slender nerves do arise from the 



