REPORT OF EXECUTIVE COMMITTEE. 1 35 



the chitons, from pleural nerve-cords ; in lamellibranchs and marine 

 gasteropods, from the visceral ganglion or ganglia ; in pulmonates 

 and cephalopods, from the suboesophageal ganglion. In the gastero- 

 pods the nerve-fibers enter the heart both at the auricular and at the 

 aortic ends. 



The arthropod heart is supplied with both inhibitory and acceler- 

 ator fibers, the latter coming from the central nervous system ante- 

 rior to the former, a condition similar to that in the vertebrates. 

 The cardiac nerves of the lower gasteropods (chitons, prosobranchs, 

 tectibranchs) appear to be only accelerator in function. In the 

 nudibranchs and the pulmonates both inhibitor and accelerator car- 

 diac nerves are present. In the lamellibranchs and the cephalopods 

 the main, if not the sole, function of the nerves is inhibitory. 



In Limulus the heart-muscle does not possess automaticity. The 

 heart-beat is neurogenic, or due to the activity of the ganglion cells 

 on the dorsal surface of the heart. There is some evidence that the 

 heart-beat in the other invertebrates is also neurogenic. 



In Limulus the coordination or conduction in the heart takes place 

 in the nervous and not in the muscular tissues. 



In Limulus the cardio-inhibitory nerves act on the ganglion cells 

 in the heart and not directly on the heart-muscle. 



The arthropod, the molluscan, and the tunicate heart exhibit no 

 refractory period, but the excitability is lowest at beginning of sys- 

 tole. The amplitude of contraction varies with the strength of the 

 stimulus. The heart can be tetanized. 



Single induced shocks, as well as the interrupted current of a cer- 

 tain intensity sent directly through the arthropod, the molluscan, and 

 the tunicate heart, produce inhibition of the rhythm, partial or com- 

 plete. This inhibition is due (i) to the stimulation of inhibitory 

 ner\'e-endings in the heart, (2) to direct action of the electrical cur- 

 rent on the rhythmical tissue. In Limulus this direct action of the 

 current is on the automatic ganglion cells and not on the muscle, and 

 this is probably true of the other invertebrates. This action of the 

 induced current on the ganglion cells is probably of the nature of 

 overstimulation or "shock." 



Solutions of curare, atropin, and nicotin of sufficient strength to 

 affect the heart accelerate the rhythm ; strong solutions produce 

 tetanus or "tonus" contractions. 



These alkaloids paralyze (at least temporarily) the inhibitory 

 nerves in the heart, but not the accelerator or motor nerves. 



In Limulus the accelerator action of the.se drugs is on the ganglion 



