The anatomy of Lncapina creniilata. 



47a 



nerve (1) from the gill gaüglion is that running forward and connect- 

 ing with the anterior mantle nerve. It is a short nerve, but its 

 special interest lies in the fact that it completes a loop made by 

 nerves arising from different sides of the pleural ganglia. A small 

 nerve (Mf) springs from the inside of the gill ganglion, and runs back 

 and up through the dorsal wall of the mantle cavity. Near the mantle 

 fissure this nerve bifurcates, one part going each way around the 

 opening (Fig. P). These nerves from the two sides join each other 

 forming a complete anastomosis around the mantle fissure. The fourth 

 or smaller nerve (6) leaving each gill ganglion is that running back 

 along the afferent sinus to the auricle of the heart. This nerve lies 

 under a thin layer of tissue, and 

 can not be seen under ordinary 

 conditions but a nitric acid pre- 

 paration usually showes it well. 

 The anastomosis of this nerve 

 seen in Fig. O, continues back 

 into the walls of the auricle. 



The circum-pallial chord, or 

 mantle ring nerve (Cjj. Ch) is a 



chain of small ganglionic centers ex- 

 tending entirely around the mantle. 

 This cord lies just outside the 

 palliai sinus in the tissue where the 

 mantle joins the wall of the visceral cavity. Its general position with 

 its branches and its relation to the blood vessels will be seen in 

 Fig. D. The nerves coming to the mantle (P. P. con) from the pleural 

 chords all join this palliai chord, in the little ganglionic centers. 

 Heretofore these nerves from the pleural, have been designated as 

 lateral nerves, but since we now know their relation to the mantle 

 ring nerve, it seems to me it would be better to call them pleuro- 

 pallial connectives. Only a few of these have been completely drawn 

 in PI. 33 (large Fig.) in order to avoid confusion with the other 

 nerves. Both the pleuro-pedal ganglia and these connectives lie close 

 upon the floor of the visceral cavity, surrounded by thin-walled blood 

 vessels. Thus it is very easy to follow the course of the connectives 

 to the point where they enter the wall, and it is not a difficult matter 

 to dissect them out to their union with circum-pallial chord. 



The anterior part of the mantle ring nerve is somewhat larger 

 than any of the rest. It receives an additional nerve supply through 



31* 



Fig. P. Nerves around mantle fissure. 

 3If Connective to gill ganglion. 



