138 A. J. CARLSON. 



At this point a small nerve (2) is given off to the dorsum of the 

 neck. In some specimens the ganglion is not situated at the 

 point of origin of the nerve but nearer the visceral ganglion. 

 The right visceral ganglion gives off peripherally one stout nerve 

 (5), which enters the osphradium ; here it divides and sends 

 branches into the gill and to the roof of the gill chamber. The 

 left ganglion gives off a corresponding nerve (6), which also 

 bifurcates soon after leaving the ganglion. At the point of bifur- 

 cation is a small ganglion. One of the branches enters the in- 

 ferior pallium, the other the posterior dorsum. Either visceral 

 ganglion gives rise to another nerve (3, 4), much smaller than the 

 one that takes its origin at the posterior end. These nerves 

 unite in a small ganglion (7) situated to the left of the two main 

 ganglia. This ganglion is called the " genital ganglion" by 

 Vayssiere, which is not a well chosen name, because the nerve 

 that leaves the ganglion supplies not only the reproductive glands 

 but also the renal organ and the heart. The nerve (8) that is 

 given off by the ganglion soon bifurcates and at the point of bifur- 

 cation is another ganglionic enlargement (9). The main branch 

 (10) takes a lateral direction and enters the genital glands, the 

 other passes towards the pericardial cavity. This branch of the 

 nerve sends a small filament on to the aortic sinus (i i), while the 

 main trunk passes posteriorly and median in the pericardium 

 ventral to the heart, finally entering the kidney (14). Several 

 small branches are given off to the pericardium, one of which 

 can be followed to within one or two mm. of the base of the auri- 

 cle, but not on to the auricle itself. The branch to the aortic 

 sinus ramifies on the sinus making almost a complete ring at the 

 ventricular junction. A branch can be followed on to the ventricle. 

 In Aplysia I was unable to trace a nerve on to the ventricle, in 

 Bulla I failed to trace the nerve to the auricle ; but the physio- 

 logical evidence is conclusive that fibers from the nerve (8) enter 

 the auricle of Bulla at its base. The connection is probably 

 with one of the tiny branches in the ventral wall of the 

 pericardium. 



In PlcurobrancJuva (PI. IV., Fig. 12) the pleural ganglia consti- 

 tute the postero-lateral portion of the supra-cesophageal ganglion. 

 The first pair of nerves that proceeds from the posterior and lat- 



