ACTINIAN BEHAVIOR 195 



Jennings ('05, p. 449) and in Cribrina as reported on by Gee 

 ('13, p. 314), the mouth during feeding is moved by the oral 

 musculature toward the food-bearing tentacles, a shifting which 

 has also been observed in certain corals (Carpenter, '10). This 

 operation, though it can be seen to occur in Metridium, is rela- 

 tively so insignificant in this form that it may be passed over 

 without comment; the important elements in the feeding of this 

 actinian are the five already mentioned. 



Much confusion and uncertainty exists in the various accounts 

 of the methods by which actinians obtain their food and more 

 or less of this is due to the failui^e on the part of writers to desig- 

 nate the particular form of activity that they are for the moment 

 discussing. Thus both cihary and muscular activity are involved 

 in the appropriation of food and have often been indiscriminately 

 dealt with in accounts of this operation. Their significance for 

 the animal as a whole is, however, very different and it is, there- 

 fore, highly desirable that they should be kept clearly in mind 

 as separate processes in any discussion in which they are in- 

 volved. 



Of the five principal events that go to make up the act of 

 food appropriation, three exhibit so little variation that they 

 may be regarded as essentially uniform. These are the secre- 

 tion of mucus, the beat of the tentacular cilia, and the opening 

 of the esophagus. In none of these are there during feeding any 

 important readjustments w^hich are essential to the acquisition 

 of food; the production of mucus is apparently a strictly local 

 response to a local stimulus; the beat of the tentacular cilia is 

 constant and irreversible; and the opening of the esophagus is 

 as simple and mechanical a reflex as could well be imagined. 

 The idea that the esophagus, as often intimated, exhibits peri- 

 stalsis is probably incorrect. At least a careful inspection of 

 this organ in action in Metridium gives no support to this idea. 

 The two remaining events in the appropriation of food, the 

 responses of the oral ciha and the movements of the tentacles, 

 are both open to significant changes and are of the utmost 

 importance in judging of the relation of this process to the 

 actinian as a whole. 



