IJ2 A. J. CARLSON. 



branchial ganglia to the auricles, nor did I find any physiologi- 

 cal evidence of their existence. If such a nervous connection 

 exists, the nerves are evidently only sensory in function. The 

 auricles are, however, innervated from the visceral ganglion. 



The nervous system of Lucapina differs from that of Haliotis 

 chiefly in the presence of two large ganglia, the intestinal ganglia, 

 on the course of the pleuro-visceral commissures. From the 

 posterior side of the visceral ganglion (PI. V., Fig. 8) a compara- 

 tively large nerve passes in a dorsal direction in the wall of the 

 basibranchial sinus towards the rectum, but before reaching the 

 rectum the nerve bifurcates, one branch passing on either side of 

 the rectum to take an anterior course in the walls of the afferent 







gill sinuses. From the ganglion and from the nerve between 

 the ganglion and the point of bifurcation two or three small 

 nerves are given off (3, 4), and branches from these nerves can 

 be followed into the pericardium. Illingworth states that he 

 could trace some of these branches into the musculature of the 

 ventricle along the rectum. I was not able to do so, and the 

 physiological evidence is to the effect that the nerve enters the 

 ventricle at the aortic end and not along the rectum. After 

 the bifurcation, each nerve gives off a small branch that can be 

 followed to the base of the auricle (5). From the gill ganglia sev- 

 eral nerves are given off, but the only one that concerns our 

 present inquiry is the tiny nerve described by Illingworth as 

 passing posteriorly in the walls of the efferent branchial sinus, 

 branching and anastomosing on its course, to finally end in the 

 musculature of the auricle. I was able to follow the nerves (9) 

 for some distance towards the base of the gills, but not on to the 

 auricles. Stimulation of the efferent gill sinus does not influence 

 the auricles, so that if this nervous connection, described by 

 several investigators for so many species, is present in Liicapina 

 the nerves are in all probability only sensory in function. The 

 auricles of Lncapina, like those of Haliotis, are innervated from 

 the intestine-visceral commissures or the visceral ganglion, as 

 shown by stimulation of the commissures. The exact course of 

 these auricular nerves remain to be worked out. 



4. The Monotocardic Prosobranchs. - - Nerves to the heart of 

 the monotocardic prosobranchs have been described by Haller 



