II] HABITS OF CONVOLUTA 65 



below, and regards the phenomenon as a manifestation 

 on the part of C. roscoffensis of " memory of the shock 

 of the waves." Certainly, if all other explanations fail 

 if we can discover no agent which serves to jog this 

 memory we must accept this suggestion ; though in 

 doing so, it might be well to ask ourselves whether it 

 is to be regarded as an explanation or as a succinct 

 statement of our ignorance. 



Experimental investigation of the phenomenon 

 would appear to indicate that no such large demand 

 on memory or mneme as that which is implicit in 

 the above hypothesis need be made. 



In the first place, as we have noted already, 

 C. roscoffensis does not remain on the surface of 

 the sand at night. Hence we must suppose, on the 

 memory hypothesis, either that it forgets to arise from 

 the dark sand when it is dark on the surface, or that 

 it remembers, rises, and finding nothing better to do, 

 goes to bed again. 



The behaviour of C. roscoffensis in constant dark- 

 ness is yet more difficult of interpretation on this 

 hypothesis. For, when kept in continuous dark- 

 ness, C. roscoffensis ceases to exhibit periodicity of 

 alternate up and down movement. There may be 

 one movement downward and one upward ; but, after 

 that, the animals remain upon the surface of the 

 sand day after day until they die (Fig. 13). 



Again, if the downward movement is due to a 



K. 5 



