PHYSIOLOGY OF THE INVERTEBRATE HEART. 129 



the influence of the nerves on the heart, but after the auricles 

 have been severed, leaving the other connections intact, stimula- 

 tion of these nerves or the visceral ganglion has no further effect 

 on the heart. 



Platydoii differs from Tapes in that the reno-cardiac nerves (3) 

 are given off from the visceral ganglion instead of from the com- 

 missures. A small ganglion (4) can also be made out on these 

 nerves at the base of either auricle. 



In Venus, Cardinal, He unites and Pcctcn the cardiac nerves 

 were not worked out in detail, but the heart of these lamelli- 

 branchs is innervated from the visceral ganglion or the cerebro- 

 visceral commissures just as in My a and Tapes, as will be shown 

 by physiological experiments in a subsequent paper. This is 

 evidently the plan of the reno-cardiac innervation in all lamelli- 

 branchs. The cell bodies of the cardiac nerves are probably 

 situated in the visceral ganglion or ganglia, the giving off of the 

 nerves from the cerebro-visceral commissures instead of from the 

 ganglion directly is evidently only a case of the fibers following 

 the course of the commissures for some distance before turning- 



o 



laterally to enter the kidney and the heart. While it is certain 

 that the heart of these molluscs is innervated from the visceral 

 ganglion, the nerves entering the heart at the base of the auri- 

 cles, the exact course of these nerves through the renal organs 

 as well as in the heart itself remains to be worked out. This 

 must be left to biologists who have more suitable material, like 

 Tridacna, at their disposal. 



Young (1881) studied the effect on the heart of the stimulation 

 of the visceral ganglion in the lamellibranchs My a, Anadonta and 

 Solen. He gives no definite description of the course of the 

 nerves from the visceral ganglion to the heart. He mentions two 

 tiny nerves which he could trace from the ganglion on to the 

 pericardium and the rectum, thinking that these were the cardiac 

 nerves. From his statement that branches from these nerves 

 pass to the rectum he evidently refers to nerves similar to those 

 indicated by me in My a and Mytilus as dorsal mantle nerves (Fig. 

 /, 6, 10 ; Fig. j, 2) ; but the physiological evidence goes to 

 show that these nerves do not enter the heart. 



2. The Chitons.- -The chitons present a more diffused nervous 



