190 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The outer edge of each pedal ganglion is fringed with numerous tine nerves. These nerves 

 may be separated into two groups. The first of these are small, very slender nerves, which spring 

 from the anterior or upper side of the edge of the ganglion. These nerves go to the tentacles of 

 the superior labial groups: in the male, the nerves of the spadix and antispadix also are included 

 in this series. The nerves of the tentacles of the spadix are. however, much larger than the 

 nerves of the superior labial tentacles, or of the tentacles of the antispadix. In one dissection I 

 found a quite peculiar nerve (HO); it passes from the left pedal ganglion into the base of the first 

 cirrus of the spadix. where it ends in an enlargement from which a number of small branches 

 proceed into the surrounding tissues. 



The apparently similar innervation of the superior labial tentacles and the tentacles of the 

 spadix and the antispadix points to the latter being separated portions of the superior labial 

 groups. But it is not safe to rely overmuch upon the, at present very slight, evidence of the 

 innervation. The nerves arising from the pedal ganglia are too little separated for us to 

 distinguish accurately between one group and another. 



The second series of nerves are much larger than the first and arise from the lower or pos- 

 terior portion of the edge of the ganglion, or even from the side pressed against the cartilage. 

 They proceed to the individual digital tentacles (9). 



Several large nerves leave the upper (or outer) ends of the pedal ganglia, near the junction 

 with the cerebral and pleuro-visceral ganglia. From these nerves (10) branches proceed to some 

 of the digital tentacles and to the hood. 



Finally, a large nerve leaves the pedal ganglion very close to its junction with the other 

 ganglia. The two main branches into which this divides become the nerves of the preocular and 

 postocular tentacles. Finer branches proceed to the posterior portion of the hood, and some- 

 times to cirri of digital tentacles. 



Numerous nerves, large and small, arise from the posterior edge of the pleuro-visceral 

 ganglion. The nerves of the two sides are separated by a narrow median interval free from 

 nerves. On either side of the interval a huge visceral nerve (22) leaves the ganglion and runs 

 straight backward, lying upon the inner surface of the body wall at the side of and parallel to 

 the vena cava. At the posterior limit of the mantle cavity the visceral nerve turns outward and 

 forward in the mantle, finally dividing into two branches which extend into the gills (19 and 20). 



Before the visceral nerve divides to form the branchial nerves 1 have found it to give off' 

 two branches, which seemed to pass into the posterior walls of the renal sacs ( 17 and 18). 



Just before the visceral nerve bends into the mantle it gives off small nerves to the 

 spermatophore sac and genital duct (16). 



Frequently connected with the visceral nerves are a pair of slender nerves which pass to the 

 dorsal wall of the vena cava (15 and 21). These are, however, very variable in their origin. 

 Always present, they sometimes both arise from the visceral nerves at about the middle of their 

 course in the body. Sometimes both arise directly from the pleuro-visceral ganglion just inside 

 the origins of the visceral nerves, as is figured by Willey; or one may arise from the pleuro- 

 visceral ganglion, while the other springs from some portion of the visceral nerve, as is shown 

 in Fig. 41. 



Willey is quite sure that these nerves innervate the preanal papilla-, and partly for this 

 reason considers the papillae as the anterior pair of osphradia. I have not been able to trace the 

 nerves anywhere but to the walls of the vena cava; although this does not constitute proof that 

 they end there. 



Laxkastkr and Bourne state absolutely. Willey with confidence, that they have traced a 

 small nerve from the bifurcation of the branchial nerves into the interbranehial papillae. This 

 branch also I have been unable to find, either in several dissections or in a series of sections of 

 the papilla. 



Outside the visceral nerves a number of nerves of various sizes leave the pleuro-visceral 

 ganglion and extend into the shell muscles and the body wall (14). The number of these is much 

 larger than is represented in Fie-. 41. only the larger ones being drawn. 



From the extreme ends of the pleuro-visceral ganglion a few very small nerves extend into 



