190 MEMOIRS OF THE NATIONAL ACADEMY OF S(TENCES. 



The outer edge of eaeii pedal giiaglion is t'l'inged with muuerous hue nerves. These nerves 

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

 fi"()in 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, oi- of the tentacles of the antispadix. In one dissection I 

 found a <juite peculiar nerve (80); it passes from the left pedal ganglion into the liase of the tirst 

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

 proceed into the surrounding tissues. 



The iippai-ently similar innervation of the superior labial tentacles and th(> tentacles of the 

 spadix and the antispadix points to the latter l)eing separated portions of the superior labial 

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

 itmervation. The nerves arising from the pedal ganglia are too little sejiai-ated for us to 

 distinguish accurately between one group and anothei-. 



The second series of nerves are much larger than thi^ 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. 

 Thev proceed to the individual digital tentacles (9). 



Several larg(> 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 ])roceed 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 ])ranches into which this divides Vjecome 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 large 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, linally dividing into two branches which extend into the gills (W and 20). 



Before the viscei'al nerve divides to form the l)ranchial nerves I 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 otl' small nerves to the 

 spermatophore sac and genital duct (Iti). 



Frequently connected with the visceral nerves ar(> 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 viscei-ai nerv(>s, as is tigui-ed Ijy AVii^i.ky; or one may arise from the pleuro- 

 \dsceral ganglion, while the other springs f I'om some portion of the visceral nerve, as is shown 

 in Fig. 41. 



WiLLKY is quite sure that these nerves innervate t\w preanal papilhe, and partly for this 

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

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

 they end there. 



Lankastkr and Boiunk state absolutely, ^VILLEY with contidence, that they have traced a 

 small nerve fi-om the bifui-cation of the branchial nerves into the interbranchial papilhe. This 

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

 the i)apilla. 



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 repr(>sented in Fig. 41. only the larger ones being drawn. 



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



