218 G. H. PARKER 



and by Jordan ('08). It involves the animal as a whole and 

 yet it persists as strikingly in small fragments of an actinian as 

 it does in the whole (Wolff, '04), Hence in this respect it gives 

 no ground for the assumption of a specially unified state. The 

 limp toneless condition of a muscle isolated from its nerve in a 

 higher animal is in strong contrast to the tightly contracted 

 fragment from an actinian's body. 



The tidal and nychthemeral rhythms of these animals, as 

 described by Bohn, are much more suggestive of organic unity 

 than the single act of retraction itself. This is especially true 

 when we take into account the retention of this rhythm after 

 the removal of the rhythmic stimulus. Such activities imply 

 the origin of new internal states through past stimulations and 

 their retention in the subsequent modes of response of the ani- 

 mal as a whole. But it is by no means easy to judge of the value 

 of Bohn's observations in these directions. His first description 

 (Bohn, '06 c) of the rhythms and their retention was relatively 

 simple, but his subsequent account shows such diversity and 

 complexity that it is difficult for the reader to convince himself 

 that rhythms have really been observed. Jennings ('09), who 

 accepted Bohn's earlier observations with enthusiasm, was led 

 in this way to entertain grave doubts about the accuracy of 

 much that had been claimed. The fact that Pieron ('08 e) 

 reexamined the question of the persistence of tidal rhythm in 

 Actinia without being able to confirm Bohn's statement about 

 it, and that Gee ('13) and I have been absolutely unable to 

 find any evidence of retained rhythms, either tidal or nych- 

 themeral, in the actinians that we have studied leads me to 

 conclude that, though actinians may exhibit rhythms in conse- 

 quence of rhythmic stimuli, they do not retain these rhythms 

 on the disappearance of the stimuli. If retained rhythms do not 

 occur in actinians, they can not of course be called upon as evi- 

 dence of complex unified nervous states in these animals. 



Intimately associated with the retention of rhythm in actin- 

 ians is the retention of characteristic positional responses. Jen- 

 nings ('05, p. 461) has shown that an Aiptasia will assume an 

 irregular and distorted form in consequence of the irregularities 



