ACTINIAN BEHAVIOR 219 



of the rocky cavity in which it has taken up its abode and that 

 it will retain this shape for some time after it has been removed 

 from its retreat. Moreover irregular forms of some permanence 

 can be artificially and quickly produced by putting an animal 

 into an artificial, irregularly shaped chamber. Such irregular 

 forms are wHhout much doubt due to differences in the degree 

 to which tonicity is developed on particular parts of the animal's 

 body by variously disposed stimuli. When it is remembered 

 that the tonicity of general retraction may continue in some 

 actinians even for days, it would not be surprising if an irregu- 

 larly distributed tonicity should also have a lengthy period. 



Van der Ghinst ('06) has also pointed out an interesting case 

 of the retention of a characteristic positional response in Actinia. 

 Specimens of this sea-anemone are found attached either to the 

 undersides or to the uppersides of rocks. When individuals 

 from both locations are collected and put in an aquarium in 

 which both positions are possible, those that were originallj^ on 

 the underside of rocks reassume this position and those that 

 were above move to the uppersides of objects. The positional 

 -relation apparently impressed upon them by their previous en- 

 vironment thus reasserts itself and in this manner gives evidence 

 of modified central activities. The habit is said to be lost in 

 twenty-four to forty eight hours. 



The species of sea-anemones with which I have worked are 

 not often found in the two positions assumed by Actinia and 

 I have therefore not been able to carry out experiments on the 

 lines worked on by Van der Ghinst. As no one seems to have 

 repeated these observations on Actinia or other sea-anemones, 

 and as Van der Ghinst himself claims for the retention of the 

 response only the brief period of a day or so, it seems to me that 

 they call for confirmation before they can be taken seriously 

 into account in a discussion like the present one. 



A third form of response which may be taken to involve the 

 actinian as a whole is creeping. Locomotion by means of the 

 pedal disc in these animals has already been rather fully dis- 

 cussed (Parker, '17 b) and it has been pointed out that this 

 operation can be successfully carried out by specimens of Sa- 



