482 PROCEEDINGS OF THE ACADEMY OF [Sept., 



dorsal to the oesophagus and to the right side of the stomach and 

 the adjacent section of the intestine. The visceral connective on 

 the left develops a small nerve, usually associated with a ganglionic 

 enlargement, which has been traced for a. short distance beneath 

 the floor of the mantle cavity. The visceral ganglion itself also 

 gives rise to a branch which passes to the wall of the kidney, 

 where it disappears from view. 



In this species a well-defined marginal mantle nerve, or Mantel- 

 randnerv, is present with many of the essential features of what has 

 been found by Willcox ('98) 3 to exist in Acmcea fragilis. In the 

 present instance it is loosely attached to the walls of the marginal 

 mantle sinus, and throughout its course develops numerous delicate 

 branches, which attach to the overlying epithelium or the deeper- 

 seated gland cells. On the right side of the body this marginal 

 nerve is united by two connectives with the pleural ganglion, 

 and, judging from sections, with the sub-intestinal ganglion as well. 

 Of these connectives the anterior is much the heavier, and skirting 

 the floor of the mantle cavity can be followed forward, where it 

 divides into a short, lateral branch uniting with the marginal nerve 

 coming up from the posterior three-fourths of the body, and a slightly 

 more dorsal and relatively larger nerve coursing about the base 

 of the marginal mantle thickening. In other words, the marginal 

 mantle nerve of the posterior part of the body can be traced as far 

 forward as the anterior level of the head in contracted specimens. 

 It actually may continue entirely around the body, but anteriorly 

 it becomes very delicate and finally disappears among the masses 

 of gland cells in the free border of the mantle. However, the heavy 

 connective from the right pleural ganglion attaches to it before its 

 disappearance, and on the other hand extends around the mantle 

 edge in front, where it meets the corresponding nerve from the left 

 pleural ganglion, thus completing the circular mantle nerve, though, 

 as noted before, this anterior section is at a slightly greater distance 

 from the mantle border. The smaller, posterior connective appears 

 to be more largely a product of the sub-intestinal ganglion, and, 

 like the two smaller connectives of the left side, it extends laterally 

 and posteriorly through the pedal musculature to the mantle border. 

 These two smaller connectives of the left side as well as another of 

 much larger caliber arise from the pleural ganglion. The anterior 

 one pursues a course similar to its counterpart on the right and is 



3 Zur Anatomie von Acmsea fragilis, Jenaische Zeitschr.f. Naturw., Bd. 32, 1898. 



