PHYSIOLOGY OF THE INVERTEBRATE HEART. 139 



eral side of the ganglion enters the mantle, the nerve on the right 

 side also sending branches to the gill. From the second pair of 

 lateral ganglionic protuberances are given off three nerves, one 

 from the right side and two from the left. The posterior one on 

 the left side, the larger of the two, enters the posterior part of the 

 mantle of the same side. The other nerve (/w/) follows the course 

 of the cerebro-pedal and pedal commissures towards the right 

 side, where it takes a posterior direction and joins the visceral 

 ganglion situated anterior and to the right in the body cavity. 

 The corresponding nerve on the right side (rim} is much stouter 

 and is probably homologous to the two nerves given off from 

 the corresponding ganglionic protuberance on the left side. 

 Peripherally the visceral ganglion gives off two nerves. The 

 nerve on the right side ( I ), the largest of the two, passes posteriorly 

 in the body cavity at the margin of the mantle and the foot and 

 enters the gill. The left nerve passes dorsally towards the peri- 

 cardial cavity, a little in front of which it enters a small ganglion 

 (3), designated by Lacaze-Duthiers as the "genital ganglion," 

 which is certainly a misnomer, because the ganglion supplies 

 other organs besides the reproductive glands. Five nerves are 

 given off by this small ganglion. One of these (10) passes on to 

 the anterior aorta and follows it along its ventral side to the aortic 

 sinus, where it bifurcates, one branch (12) passing along the lat- 

 eral, the other (13) along the posterior aorta. In large specimens 

 a small ganglionic swelling can be made out at the place of 

 branching (i i). A tiny branch (14) is given off by this ganglion 

 to the aortic sinus, but I did not succeed in tracing it on to the 

 ventricle. The smallest nerve of the five bifurcates soon after 

 leaving the ganglion, sending one branch (9) on to the ventric- 

 ulo-aortic junction, the other branch (8) is lost in the connective 

 tissue surrounding the ganglion. The nerve given off from the 

 median part of the ganglion (5) is larger. It passes posteriorly 

 to the auriculo-ventricular junction where it penetrates the mus- 

 cular bands which make up the ventral wall of the pericardium 

 and enters the auricle. Just as it enters the auricle a branch is 

 given off to the ventral wall of the pericardial cavity. The main 

 part of the nerve can be followed in the wall of the ventricle 

 almost around the entire organ. It breaks up in several branches 



