THE PHYSIOLOGY OF THE NERVOUS SYSTEM OF THE 

 RAZOR-SHELL CLAM (ENSIS DIRECTUS, CON.) 



BY 



OILMAN A. DREW 

 With One Plate 



The razor-shell clam is a particularly favorable lamellibranch 

 for the study of the functions of the ganglia, because: (i) It is 

 very active and responds rapidly to stimuli. (2) Each ganglion 

 supplies nerves to organs that are so active that one can hardly 

 fail to see movements, even when the stimulation is slight. (3) 

 The animal is so narrow that the shell valves can be wedged apart 

 enough to allow all operations and experiments to be performed 

 without removing the animal from its shell. (4) The ganglia 

 with their commissures, connectives and chief nerves, all lie so 

 superficially they can be seen without cutting the animal more than 

 to separate the fused margins of the mantle lobes and the inner 

 lamellae of the inner gills, and to expose or cut almost any one of 

 them requires only the cutting of a thin outer covering that cannot 

 cause a mutilation that needs to be taken into account in the results 

 that are obtained. 



Before discussing the functions of the diflPerent ganglia it is 

 desirable to study the activities of the animal as a whole and to 

 become acquainted with the responses of the various portions of 

 the body when the organs that are subject to external stimuli are 

 stimulated. 



The habits of the animal have already been discussed in another 

 paper,^ but in studying the effect of stimuli it is necessary to know 

 something of the normal life of the animal, and accordingly a 

 brief statement of its habits are desirable here. The animals are 

 best known on mud-flats that are exposed at low tide, but they are 



^ The habits and movements of the Razor-shell Clam, Ensis directus, Con. Biol. Bui., vol. xii, 

 no. 3, 1907. 



The Journal of Experiment.'^l Zoology, vol. v, no. 3 



