MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 189 



the ventral side of the buccal mass, where thej enter the buccal nervous system (5 and 6). These 

 are the outer and inner cerebro-buccal connectives of each side. The buccal connectives are of 

 considerable length. In preserved and contracted specimens they are found to make, numerous 

 loops, which provide the extra length required when the buccal mass is thrust forward. 



The buccal nervous system consists of two pairs of ganglia united by connectives and two 

 commissures passing anterior to the oesophagus. The cerebro-buccal connectives pass through 

 the muscular membrane which covers the ventral surface of the buccal mass and unite with the 

 pharyngeal ganglia — slender ganglia lying at the sides of the ventral surface of the buccal mass, 

 immediately upon the lower edge of the mandibular muscles (4). The pharyngeal ganglia are 

 united by the long pharyngeal commissure passing anteriorly along the edge of the lower 

 jaw (2). From the posterior ends of the pharyngeal ganglia strong connectives extend backward 

 and inward to the buccal ganglia at the sides of the oesophagus as it issues from the buccal mass 

 (32). The buccal ganglia are quite small. They are connected by a commissure passing around 

 the anterior side of the oesophagus {'■'•'■'•). 



Numerous nerves are given off by the pharyngeal ganglia to the mandibular muscles. A 

 nerve arising on the posterior side of the buccal ganglion bends over the dorsal side of the latter 

 and passes to the salivary gland (34). A small nerve passes from the buccal ganglion to the 

 oesophagus (31 ). Other nerves seem to pass into the tongue, but could not lie accurately traced. 



A number of small nerves (more than a dozen) leave the anterior side of the cerebral ganglion 

 between the bases of the inner cerebro-buccal connectives and pass forward upon the dorsal sur- 

 face of the buccal mass (-27). Some of these nerves or their branches enter the mandibular 

 muscles. The majority of them pass into the space between the folds of the buccal membrane 

 and -are distributed to the papilla' along the edge of the membrane. 



A few small nerves (23) leave the posterior sides of the outer ends of the cerebral ganglion 

 and pass to the posterior portion of the dorsal buccal retractors close to their attachment to the 

 cartilage. These seem to be the same nerves which Valenciennes describes as proceeding to the 

 cavity of the cartilage which he mistook for the otocyst. 



In one specimen I have been able to trace the otocystic nerves. They are small, of about 

 the same size as the nerve figured as going to the post-ocular tentacle. Each arises from the 

 dorsal surface of the cerebral ganglion, just above the base of the optic nerve. As the otocyst 

 is pressed between the posterior surface of the pedal ganglion and the cartilage, the otocystic 

 nerve passes into the angle between the cerebral and pedal ganglia and then runs along the 

 posterior surface of the pedal ganglion. The tunic of the nerve is so closely attached to that of 

 the pedal ganglion that the nerve seems at first sight to spring from this ganglion. The nerve 

 spreads out fan-wise upon the surface of the otocyst. 



The nerve of the rhinophore seems to leave the cerebral ganglion close to the base of the 

 optic nerve, but I am not entirely sure of its course. 



No nerves are given off from the inner edges of the pedal ganglia, but from the outer edges 

 arise exceedingly numerous closely set nerves. These nerves are distributed entirely to the 

 funnel, the labial tentacles, and the digital tentacles and the cephalic sheath. In other words, 

 they pass only to those parts which some consider to be homologous with the foot of other 

 mollusca. 



The infundibular nerves are a pair of large nerves leaving the inner end of each ganglion, 

 passing forward and downward into the tissues of the funnel (8). They are situated at either end 

 of the pedal commissure, from which no nerves arise. For the first part of their course the 

 infundibular nerves lie in a cavity slightly larger than themselves, probably a blood space. 



Just outside the infundibular nerves two conspicuous but smaller nerves (7) pass forward 

 from the pedal ganglia to the inferior labial lobes in the female or to their homologue in the 

 male. Van dee Hoeven's organ. The nerves enter the base of the inferior labial lobe; they 

 enter Van dee Hoeven's organ at about the middle of each side. In each case after the nerves 

 have entered they expand into small ganglia (35). from wrnich nerves are given off to the separate 

 tentacles of the organs. Fig. 41 is drawn from a male specimen in which the nerves pass inward 

 from the ganglion instead of forward as in the female. 



