PHYSIOLOGY OF THE INVERTEBRATE HEART. 14! 



the anterior aorta it follows the latter in a median direction to- 

 wards the hind gut, where it bifurcates. The smaller branch 

 (i) continues in the median direction along the artery and, pass- 

 ing- ventral to the hind gut, it can be followed to the left ventral 



o & 



side of the aortic sinus. The main branch passes posteriorly, on 

 the left side of and close to the hind gut. At the level of the 

 ventricle it gives off a small branch (2) which passes in a median 

 direction dorsal to the hind gut and enters a small ganglion situ- 

 ated on the aortic sinus (6). From this ganglion one or two 

 branches can be traced on to the aorta and another on to the 

 ventricle. This ganglion evidently corresponds to the two ganglia 

 described by Hancock and Embleton in Doris tuberculata as 

 situated on the "apex of the ventricle." The main branch of 

 the nerve continues posteriorly along the gut to the anal region. 

 On this course the nerve gives off a branch (3) to the ventral 

 wall of the pericardium and probably also to the renal organ. 

 The terminal branches of the nerve (4, 5) pass to the base of the 

 auricle and to the gill. There appears to be a small ganglionic 

 swelling on the nerve before it breaks up into the gill branches. 

 I was not able to follow the nerve into the auricle, but the phys- 

 iological evidence show clearly that nerve fibers from this nerve 

 enter the auricle at its base. 



In Triopha carpentcri (PI. VI., Fig. 15) the central nervous 

 system is fused into one ganglionic mass situated dorsal to the 

 oesophagus, just as in Montereina. From each postero-lateral 

 horn of the ganglion proceeds one nerve which innervates the 

 mantle (i , 2). From the posterior and right side of the ganglion, 

 ventral to the origin of the right mantle nerve, four small nerves 

 take .their origin. The destination of two of these (5, 8) could not 

 be made out with certainty, but the other two nerves supply the 

 viscera. The nerve furthest to the right (7) enters a small gang- 

 lion (gi.~) situated on the vagina. This ganglion sends branches 

 to the copulatory organs and the reproductive glands. The 

 other nerve (6) passes posteriorly in the median line dorsal to 

 the visceral mass. On this course the nerve gives off several 

 tiny branches which cannot be followed for any distance from the 

 nerve on account of their minuteness. The largest branch 

 probably enters the intestine and the liver (9). The main trunk 



