320 W. J. CROZIER 



The possibility presents itself that the stimulus to pulsation 

 normally arises outside the cloacal region, and that the cut-off 

 pieces continue to pulsate from a sort of 'habit' or 'organic 

 memory.' It, indeed, is possible to impress rhythms upon holo- 

 thurian structures, as I have discovered in certain experiments 

 upon the physiology of the 'shading reflex.' Shadows were cast 

 upon the anterior end of a Holothuria surinamensis at 0.25 

 minute intervals, to which the animal reacted (cf. Crozier, '14, 

 '15) by more or less complete retraction of the tentacles and 

 contraction of the buccal sphincter; after the 115th successive 

 stimulation and reaction, the rhythmic shading was discontinued, 

 but the animal continued to retract the tentacles, etc., at very nearly 

 0.25 minute intervals for the next succeeding 3 minutes (i.e., 11 

 times), after which the 'reactions' became of irregular occurrence. 

 This observation was repeatedly confirmed.^ But the fact that 

 the rhythm of the isolated anal parts could be caused to stop, 

 by appropriate sensory stimulation, and then to resume again in 

 perfectly reversible fashion, argues against this interpretation, 

 as does indeed the whole behavior of the pieces in different salt 

 solutions. 



c) Mutilation experiments. Stichopus having the oral end, 

 including the nerve ring, amputated, continued to exhibit rhyth- 

 mic anal movements like those of the whole animal. As long as 

 the new anterior end remained closed by the close approximation 

 of the inturned edges of the cut, so that some internal fluid 



^ Quantitative investigation of this phenomenon is contemplated, and should 

 provide important data relative to the physico-chemical nature of 'protoplasmic 

 memory.' Somewhat comparable i-hythms of short period, impressed by experi- 

 ment, are not unknown among plants. It is especially to be noted that the 

 condition here described in Holothuria is one of 'positive memory,' in contrast 

 to the 'negative memory' [the terms are my own] studied by Pieron ('09, and 

 subsequent papers), who investigated the law according to which the sensitivity 

 of snails to rhythmic shading was abolished. Pieron was, I believe, dealing with 

 a condition primarily of sensory exhaustion. Both 'kinds of memory' are capa- 

 ble of mechanistic analysis, but that exhibited by Holothuria is more advan- 

 tageous for experimental work. I venture to predict that the study of the 

 impression of short-period rhythms upon animals, rather than the investigation 

 of 'tidal memory' (of convoluta, etc., cf. Kafka, '14, Chap. 8), will afford the clue 

 to the dynamics of ])rimitive associative memory. 



