77 



of the mantle. One of the tAvo nerves which do not enter the mantle at once 

 joins the fln branch of the pleural nerve , and the fin nerve thus formed passes 

 thru the mantle in a long oblique canal and enters the ventral angle of the fin. 

 The nerve breaks up into a number of branches which cross the upper surface 

 of the fin cartilage and ramify in the middle fascia to all parts of the fin. The 

 other nerve entei-s the canal thru which the tin nerve passes but leaves the 

 canal near its middle and supplies the mantle. 



The twii visceral nerves arise separatelj^ in the visceral ganglion and, uniting 

 as they leave the ganglion , form a median nerve which with the associated 

 viscero-branchial connective passes obliquely downward and backward thru the 

 liver to the posterior wall of the liver-case. The nerves then separate and 

 enter the cephalic retractor, at a point one third or one fourth the length of 

 the liver from its ventral end. Each nerve then passes obliquely thru the muscle 

 and runs backward beside the anterior vena cava to its termination in the neph- 

 ridial sac. The nerve passes from that point across the outer wall of the sac, 

 and finally above the branchial artery and vein to the branchial ganglion. Before 

 entering the cephalic retractor . the visceral nerve gives oft' a branch to that 

 muscle and as it emerges it gives off' two liranches: one passes outward to the 

 siphonal retractor: the other turns downward around the anterior vena cava and 

 joins its mate from the other side. The median trunk thus formed divides at 

 once : one bi'anch passes thru the mesentery-like sheet of muscle and fascia which 

 fastens the rectum to the visceral mass and enters the rectum near the distal 

 end of the duct of the ink-sac: the other branch passes back and enters the 

 upper surface of the ink-sac. A branch arises from the left visceral nerve near 

 the end of the anterior vena cava: in the male it innervates the vas deferens, 

 the spermatophoric gland , the spermatophoric sac . and the penis : in the female 

 it supplies the oviduct and the oviducal gland. A small bundle of nerve fibres 

 passes under the back end of the anterior vena cava and connects the two vis- 

 ceral nerves. The majority of the fibres seem to come from the branchial gang- 

 lion but a few appear to come from the visceral ganglion hence we are led to 

 believe that at least a part of this bundle is the branchial commissure. 



The branchial ganglia are situated in the gills and are very similar to the 

 brachial ganglia. Each is small and oval and lies at the base of the gill just 

 dorsal to the branchial artery. Prom the anterior end of the ganglion there arises 

 a nerve cord wliirli seems to be a continuation of the ganghon. This cord 

 tapers gradually from the base to the apex of the gill. It is surrounded by the 

 longitudinal mhscles of the gill, the "blood gland." and the branchial artery. A 

 nerve which seems to arise from the branchial ganglion . passes forward with 



