ACTINIAN BEHAVIOR 203 



to suppose it is, the responses of the tentacles are like those of the 

 oral ciha in that they are not especially dependent upon the 

 condition of the animal as a whole. 



As Gee ('13, p. 326) states, "the view that the seat of the modi- 

 fied responsiveness lies very largely in the individual tentacles 

 is more clearly in accord with what is known of the structural 

 organization of the sea-anemone than that the animal acts as 

 a unit." 



The appropriation of food by sea-anemones then is a process 

 which involves factors none of which necessitate the assumption 

 of the action of the animal as a whole. All are most strikingly 

 local and the changes that they exhibit are apparently entirely 

 due to fatigue. In these respects they are in strong contrast 

 with food appropriation in the higher animals, a process which 

 has become so deeply wrought into the make-up of these forms 

 that its relation to the animal as a whole is most profound. 

 While almost every one of the elements involved in actinian food 

 appropriation may be experimentally isolated and made to act 

 for itself in a most remarkably local way, scarcely any such inde- 

 pendence is observable in the parts concerned in the similar 

 operations of higher animals; the jaws and their muscles, buccal 

 glands and so forth in these higher animals exhibit a highly 

 unified action dependent chiefly upon central nervous connec- 

 tions such as is scarcely suggested in actinians, but as isolated 

 elements they have almost no reactive power at all as compared 

 with what is possible in sea-anemones. Food appropriation in 

 actinians then emphasizes rather the relative independence of 

 parts than the action of the organism as a whole. 



3. RETRACTION AND EXPANSION 



As the locomotor activities of Metridium, and in truth of most 

 other actinians, are extremely limited, the chief protective re- 

 sponse of these animals is general retraction whereby they are 

 reduced greatly in bulk, their more delicate parts are brought 

 under cover, and they shrink close to the substratum to which 

 they are attached. In many instances in fact retraction brings 

 about a withdrawal of the body of the actinian into deep, rocky 



