That the impulses giving rise to the coiitractioii of the lieart of Limnlus polyphemus arise iii gaiiglioii cells, situated chiefly (but not exclusively) in the ganglionic cord on the dorsiim of the heart, was proved by C'arlson(1). He demoiistrated that it is only by repetitive stimalatioii of the myocardium that a sustained coiitractioii in aiiy measure comparable to a normal coiitractioii can be elicited ; shoxvirig in this, aiid in other ways, that the beat is really a tctaiiic respoiise to a volley of nerve impulses in a maiiiier quite comparable to the tetaiiic contractions of tlie slreletal muscles of higher forms during volnntary coiitractioii or in response to the discharge of nil automatic center-like the respiratory eeiiter, f o r example. Iii a thoroughly wieiitific maiiiier Hoffmcziiii, in 1911 ( a ) , studied the Limulus heart, using the string galvanometer. He demonstrated tlie oscillatory character of the potential changes in the contracting muscle, obtaining electrograms similar to those which Piper (3) has obtained oil vertebrate muscles during tetaiiic reflex aiid voluntary c.oiitractioii. Hofimaiin 's worli substantiated the coiiclusions of Carlsori and many succeeding workers that the heart beat of this form was a neurogenic tetaiius, R view which is correct in its general formulation, although, as will be shown later, the tetanus is of a rather complex character. The elec-
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