468 G. H. PARKER 



with that of Wagner ('05) that nematocysts are effector organs 

 exploded by direct stimulation and not under the control of a 

 nervous mechanism. This view makes clear how these organoids 

 may be appropriated by another animal, such as a nudibranch 

 mollusk, and still retain their effectiveness, a condition which 

 would be difficult to explain if this effectiveness was in any 

 sense dependent upon nervous action. 



THE CILIARY SYSTEM 



There seems to be ample ground for assuming that large 

 ciliary organs, such as the swimming plates of the ctenophores, 

 are under the influence of the nervous system of the animals 

 in which they occur (Parker, '05 c; Bauer, '10), and it is therefore 

 natural to raise the question whether any of the cilia in Metrid- 

 ium are thus controlled. The cilia in this and other actinians 

 have been more fully studied than any other of the effector 

 systems possessed by these animals and the results of such in- 

 vestigation show in general a striking agreement. The pedal 

 disc of Metridium is without cilia. The same is true of the 

 column wall in this form (Parker '96, p. 109; Carlgren, '05, p. 



311) as well as in Halcampa and Sagartia (Carlgren, '05), though 

 in Protanthea and Gonactinia it is said to be more or less ciliated 

 (Carlgren, '05). In Metridium (Parker, '96, p. 112; Carlgren 

 '05, p. 311), Sagartia (Vignon, '01, p. 475) and Halcampa (Carl- 

 gren, '05, p. 311) the cilia of the oral disc beat toward the peri- 

 phery of that part, while in Protanthea and Gonactinia (Carl- 

 gren, '05, p. 310) their effective stroke is toward the mouth. 

 In all actinians with ciliated tentacles thus far observed the 

 ciliary currents are from the base to the tip of these organs 

 (Metridium, Parker '96, p. 110; Allabach, '05, p. 37; Carlgren, 

 '05, p. 311; Sagartia, Vignon, '01, p. 475; Carlgren, '05, p. 311; 

 Aiptasia, Jennings, '05, p. 453; Protanthea, Gonactinia and Hal- 

 campa, Carlgren, '05, pp. 310, 311). The siphonoglyphs in 

 Metridium, whether one, two, or three, possess cilia that in- 

 variably sweep inward (Parker, '96, p. 113; Carlgren, '05, p. 



312) as do also those in Sagartia (Vignon, '01, p. 475; Carlgren, 

 '05, p. 312). This fact was long ago pointed out for the alcyo- 



