EFFECTOR SYSTEMS OF ACTINIANS 473 



intimate kind than has been suggested (compare Sherrington, 

 '06) between the longitudinal mesenteric muscles and their 

 opponent, the circular muscle of the column, I do not know; 

 nor can it be stated whether or not the longitudinals work against 

 other muscles such as the transverse muscles of the mesenteries. 



There are many other ways beside changes in illumination 

 by which the contraction of the longitudinal muscles of the 

 mesenteries may be brought about. Thus a mechanical stimu- 

 lation of the tentacles or of the column wall or a chemical irri- 

 tation of these parts is almost always followed by a sudden and 

 vigorous contraction of the longitudinals, but these forms of 

 stimulation also bring into action the sphincter and the muscles 

 of the oral disc and the column, and thus carry the action far 

 beyond that of a simple muscle response. So far as I am aware, 

 a change in illumination is the only means whereby the longi- 

 tudinal and parietal muscles of the mesenteries can be brought 

 into action unassociated, as far as can be seen, with other muscles. 



Changes in illumination, moreover, are the only means which 

 I have found to call forth a partial activity of the longitudinal 

 and parietal muscles. In a general illumination these muscles 

 contract uniformly and the oral disc, retaining its horizontal 

 position, slowly descends. If, instead of illuminating a sea- 

 anemone generally, it is stronglj^ illuminated from one side, it 

 will contract much more rapidly on that side and come to rest 

 with its oral disc turned toward the light, as already pointed 

 out by Bohn ('06). This condition, which is the state of posi- 

 tive phototropism of a sessile animal or of a plant, has already 

 been observed and photographed by Hess ('13, p. 436) in Cerean- 

 thus and Bunodes, and demonstrates the partial independence 

 of the longitudinals of one side from those of the other. 



The sphincter. Many methods by which the longitudinal 

 and parietal muscles of the mesenteries are excited to action 

 also induce an ultimate activity of the sphincter whereby the 

 oral disc after its withdrawal becomes covered by the upper 

 part of the column wall. This is the usual final step in complete 

 contraction, and it is natural to inquire whether the sphincter 



