1917.] NATURAL SCIENCES OF PHILADELPHIA. 143 



with a corresponding tentacular ganglion. Each of these last-named 

 bodies is relatively small and rests in a depression between the 

 cerebral ganglia, and in every specimen carefully examined the left 

 is grooved and is considerably larger than the right. The pleural 

 ganglia are more or less spherical bodies separated by a shallow 

 depression from the cerebral and by a much deeper constriction from 

 the pedal, which are therefore more clearly defined. The cerebral 

 ganglia give rise to two or three pairs of nerves whose lettering in the 

 following paragraphs is the same as in the figures. 



CI, a nerve to the snout. In some instances this nerve has an 

 independent origin; in other cases (as in PI. XI, fig. 2, on the right 

 side) it arises as a branch of C2. In any event, it soon divides re- 

 peatedly, and, so far as traced, forms a plexus, with ganglia at the 

 nodes, that extends over the base of the snout in the middle area. 



C2 is a heavy nerve extending through the loose tissue of the 

 snout in the direction of the tentacle. About the middle of its 

 length it divides, each half with its branches passing to the inside or 

 the outside of the tentacle. The inner branch, after developing a 

 few fibers, supplying the more median portion of the head, extends 

 forward to the margin of the cowl. The outer branch, after dividing 

 once or twice, likewise pursues a course to the margin. At the 

 border of the cowl all of these nerves unite with an irregular nerve 

 lying at the base of and supplying both sets of marginal tentacles. 



C3 extends from each cerebral ganglion into the lateral portions 

 of the cowl. After branching three times the resultant nerves unite 

 with the marginal nerve. A short distance beyond its point of origin 

 a connective unites C3 with C2. 



Cx, a nerve springing from the ventral surface of each cerebral 

 ganglion close to the cerebro-buccal connective (PL XIII, fig. 10). 

 Extending anteriorly and ventrally, it enters the inferior wall of the 

 esophagus. There are indications that it anastomoses with some of 

 the nerves developed from the anterior surface of the buccal ganglion, 

 but this has not been conclusively established. 



C4, the tentacular nerve, which pursues a direct course from each 

 tentacular ganglion into the tentacle, where it rapidly disappears 

 from view among the dense mass of muscle fibers. 



Each otocyst rests upon the dorsal surface of the central nervous 

 system at the junction of the cerebral and pedal ganglion. In 

 preserved material in surface view it appears as a yellowish, spherical 

 body resting in a shallow cup of black pigmented cells. No sections 

 of it were made. 



