EFFECTOR SYSTEMS OF ACTINIANS 469 



narians by Hickson ('83, p. 694) who observed that in these 

 animals the current in the single siphonoglyph was inward 

 whereas that in the rest of the mouth was outward. 



The cilia on the non-siphonoglyphic portion of the lips and 

 oesophagus in the great majority of actinians and even in some 

 corals, ordinarily beat outward, and they may be brought by 

 appropriate stimulation to reverse temporarily and beat inward 

 (Metridium, Parker, '96, p. 109, 1905 a, 1905 b; Carlgren, '05, 

 p. 312; AUabach, '05, p. 37; Sagartia, Vignon, '01, p. 475, Torrey, 

 '04, p. 212; Tealia and Actinostola, Carlgren, '05, p. 318; Cribrina, 

 Gee, '13, p. 324; and in such corals as Fungia and Fa via, Duer- 

 den, '06, pp. 596, 604, and Isophylha, Carpenter, '10, p. 153). 

 This reversal is accomplished by the chemical and mechanical 

 stimulation of food materials. In my fu'st study of this sub- 

 ject I was led to conclude that in Metridium marginatum ciliary 

 reversal could not be accomplished by mechanical stimulation, 

 as has been demonstrated by Torrey ('04) in Sagartia davisi, 

 but subsequent work has convinced me that in specimens of 

 Metridium that have been a week or so without food, this re- 

 versal, as suggested by Jennings ('05), can be accomplished 

 by mechanical as well as by chemical means, thus confirming 

 Allabach's statement for this species ('05, p. 37). The con- 

 tinuous inward current mentioned by Carlgren ('05, p. 314) as 

 occm-ring in Sagartia viduata was seen in animals that had been 

 kept a week wdthout food and was probably in reality a tem- 

 porary'- reversal of an unfed animal to mechanical stimulation, 

 for ciliary reversal has already been observed in other species 

 of Sagartia (S. parasitica, Vignon, '01, p. 475; S. davisi, Torrey, 

 '04, p. 212). Whether the inward cuiTent in Gonactinia and 

 Protandra (Carlgren, '05, p. 310) is of this nature or hot, cannot 

 be stated with certainty, but in view of the facts just presented, 

 it seems possible. 



The cilia on the mesenteric filaments in Metridium margina- 

 tum have an effective stroke from the pedal toward the oral end 

 of these organs and, as Torrey ('04, p. 214) states, are not known 

 to be subject to reversal. The cilia of the mesenteric convul- 

 utions are very active and irreversible, but because of the great 



