PHYSIOLOGY OF THE INVERTEBRATE HEART. 147 



a posterior and ventral direction through the liver, and on reach- 

 ing its ventral surface they pass posteriorly between the liver, and 

 the viscero-pericardial sac. At this point in their course a small 

 branch is given off from each nerve to the cephalic vena cava, 

 which lies just ventral to the nerves. The two branches unite 

 into one (i i) which enters the vein, branching out anteriorly and 

 posteriorly in its muscular walls. A similar nerve to the vena 

 cava is described by Cheron for Eledone, Sepia and Loligo, but 

 he figures it as coming off from the pleural or pallia! ganglion a 

 little anterior to the point of origin of the visceral nerves. At 

 the level of the anus the two visceral nerves diverge, taking a 

 more ventral direction and half encircling the vena cava. The 

 circle is made complete by branches given off from each nerve 

 to the rectum and the ejaculatory duct of the ink gland and a 

 commissure between the two sets of nerves (i, 2, 3). The com- 

 missure passes between the vena cava and the rectum. One of 

 the branches from the left nerve (2) can be followed in the vis- 

 cero-pericardial sac near the median line almost to the posterior 

 end of the body cavity. On its course numerous branches are 

 given off to this visceral envelop, but none of these can be 

 traced to any of the cardiac organs. The visceral nerves con- 

 tinue posteriorly close to the vena cava, and at the level of the 

 ink gland, to which branches are given off (4), they take a lat- 

 eral and dorsal direction, passing dorsal to the auricles and the 

 branchial sinuses to a ganglion at the base of the gill (bg^). Be- 

 fore the nerve reaches this ganglion, that is, about 3 mm. central 

 to it, a branch (6) is given off to a small ganglion situated dorso- 

 median on the gill ventricle near the junction of the ventricle 

 with the afferent gill vein (9). From this ganglion a small nerve 

 passes on to the dorsal surface of the auricle (7). At the point 

 of entrance of the nerve into the auricle a small ganglionic en- 

 largement can be made out on the nerve (10). There is some 

 individual variation at this point. Instead of one branch from 

 the visceral nerve to the ganglion on the gill ventricle there are 

 sometimes two or three, one of which usually proceeds from the 

 gill ganglion. A branch may also run past the ganglion on the 

 gill ventricle and join the branch from this ganglion to the 

 auricle. I was not able to follow the nerves that enter the 



