EFFECTOR SYSTEMS OF ACTINIANS 467 



If a large Metridium is put in seawater containing magnesium 

 sulphate, in a very short time it becomes insensitive to stimu- 

 lation and will remain so for a long time, recovering only when 

 it is transferred to pure seawater. If from such an anaesthetized 

 animal a few tentacles are cut and these are flooded with a dilute 

 solution of hydrochloric acid in seaw^ater, they will discharge 

 their nematocysts precisely as normal tentacles do. Exactly 

 similar results can be obtained from the acontia. So far as 

 the explosion of the nematocysts is concerned, I have been 

 unable to distinguish between an acontium that has been anses- 

 thetized with magnesium sulphate and a normal one. The same 

 is true of acontia that have been treated wdth chloretone. After 

 a prolonged immersion in a solution of chloretone in seawater, 

 acontia and tentacles in which there is every reason to believe 

 that the nervous activity is completely aboUshed, wdll still 

 discharge their nematocysts on appropriate stimulation pre- 

 cisely as the unansesthetized parts do. It therefore seems 

 clear that even the circumscribed local response which has 

 been shown to be characteristic for nematocysts is not dependent 

 upon any influence that may be rightly called nervous, but is 

 determined by a direct stimulation of these elements as was 

 implied long ago by Schultze ('71). If the nematocysts contain 

 mj'ofibrils, as was first maintained by Chun ('81) for PhysaUa 

 and has since been claimed by Jickeli ('83), Schneider ('90) 

 Will ('09) and others, the acti\T.ty of these elements must depend, 

 as Will has pointed out, rather upon some form of direct stimu- 

 lation, than anj^ thing that can reasonably be called nervous. 



From the preceding discussion it seems fair to conclude that 

 the basal processes of nematocyst cells assumed by the Hert- 

 wigs to be nervous in function are in reality not so and that these 

 elements are without nervous connections, as, in fact, Hadzi 

 ('09) has recently claimed for them in Hydra. There seem to 

 be, therefore, no grounds, either anatomical or physiological, 

 for the assumption that the nematocysts are effector endorgans 

 of the nervous system and, of course, no grounds for the view 

 held by von Lendenfeld ('83, p. 369) that they are under the 

 control of the animal's will. My opinion is in entire accord 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 21, NO. -t 



