I 34 A. J. CARLSON. 



lowed to the base of the auricle, to the junction of the aorta with 

 the ventricle, and into the kidney. This arrangement is also 

 born out by the physiological experiments. Each of the two 

 nerves sends fibers to the auricle and to the ventricle by the 

 aortic end. There is some individual variation as regards the 

 point of origin of the genital and the reno-cardiac nerves from 

 the right visceral ganglion. In some specimens the nerves do 

 not leave the ganglion close together as indicated in Fig. 9, PI. 

 V., but the ganglion is distinctly bilobed and the genital nerve 

 takes its origin from the anterior lobe near the entrance of the 

 commissure. The innervation of the heart in Natica thus agrees 

 in main with that of Mnrex, Cycloplwnts and Triton as described 

 by Haller and Bouvier. There is complete agreement in the 

 innervation of the ventricle, nerves from the visceral ganglion or 

 from the visceral commissure enter the ventricle at the aortic end. 

 If the auricular nerve from the nerve plexus in the branchial 

 sinus, as described by Haller in Mnrc.v, is present in Natica, it is 

 only sensory in function, because stimulation of the branchia 

 ganglion or the nerve in the efferent gill sinus (4) has no effect 

 on the auricle. 



The innervation of the heart of Sycotypns (Fig. 10) presents 

 some differences from that of Natia, and Sycotypns being the 

 larger animal the nerves and the ganglia can be worked out with 

 greater accuracy. The right pleural ganglion gives rise to three 

 nerves, two of which (/o) unite to enter the osphradial and bran- 

 chial ganglia. The third constitutes the left pleuro-visceral com- 

 missure. On the course of this commissure some distance from 

 its entrance into the visceral ganglion in a slight ganglionic 

 swelling giving rise to a tiny nerve which ramifies in the floor of 

 the branchial chamber along the line of attachment of the gill. 

 One of its branches turns posteriorly towards the base of the gill 

 and the auricle, but I could not trace it on to the auricle itself. A 

 similar tiny ganglion on the left commissure (//) gives rise to a 

 nerve which enters the rectum and adjoining structures. The 

 left visceral ganglion, the smallest of the two, gives rise to three 

 or four small nerves, which ramify in the connective tissue 

 making up the anterior and ventral wall of the pericardial cavity. 

 One branch (2) can be traced to the base of the auricle, another 



