ACTINIAN BEHAVIOR 197 



muscular help, they bring about the swallowing of food and the 

 rejection of non-food, for under these circumstances inert mate- 

 rials were found not to reverse the ciliary stroke. Thus, as 

 Allabach ('05, p. 38) has pointed out, the reversal of the effective 

 stroke of the oral cilia is a process which is largely independent 

 of the physiological state of Metridium. 



In one particular only does this process appear to be related 

 to the general condition of the animal. Ordinarily the reversal 

 of the oral cilia is accomplished by dissolved substances from 

 the food and in my earlier studies on Metridium I was able to 

 get this reversal only by such means. Torrey ('04), however, 

 showed that in Sagartia this reversal could be brought about 

 by mechanical stimuli as well as by chemical means and that 

 it was favored by a starved condition of the animal. Allabach 

 ('05) also found that in Metridium a ciliary reversal could be 

 induced by mechanical means and Gee ('13) has recently shown 

 that specimens of Cribrina which have been in the laboratory 

 some time do not exhibit a reversal to mechanical stimuli, whereas 

 those still in their native pools give evidence of it. 



From my own reinvestigation of the question, I am led 'to 

 agree with Allabach ('05, p. 37) that in Metridium marginatum 

 some individuals on mechanical stimulation reverse their ciliary 

 stroke readily, others less readily, and still others not at all, 

 variations largely dependent upon whether the animals have 

 been starved or fed. Two underfed specimens of Metridium 

 which on being tested were found to reverse their cilia to clean 

 filter-paper were vigorously overfed and after three hours were 

 tested again with bits of clean filter-paper. In both instances 

 the paper failed to bring about a reversal of the ciha and conse- 

 quently was ejected. In another test made eighteen hours after 

 feeding, the paper was engulfed showing that the cilia had 

 returned to the state characteristic of animals that had lacked 

 food. I therefore, believe, contrary to my former opinion, that 

 an underfed Metridium will reverse the effective stroke of its 

 oral cilia to mechanical stimulation, though a small supply of 

 food will obliterate this peculiarity and leave these organs inca- 

 pable of such reversal. 



