EXPERIMENTS ON ACTINIANS 51 



probably digested. I have often repeated the experi- 

 ment, always obtaining the same result, except that 

 occasionally the string was ejected sooner, in which 

 case the meat remained on the string, partially or en- 

 tirely undigested. These phenomena have the same 

 explanation as the behaviour of insect-eating plants. 

 The chemical substances diffusing from the meat, to- 



o 



gather with the tactile stimuli exerted by it, cause a 

 bending of the tentacles that are touched in such a 

 way that they become concave and carry the meat to- 

 ward the oral opening. The contact of the meat 

 with the mouth causes the sphincter of the oral open- 

 ing to relax ; the pressure of the tentacles, together 

 with the activity of the oral disc, then pushes the meat 

 into the interior of the digestive tract. But if these 



o 



specific chemical stimuli are wanting, if we give the 

 animal, for instance, water-soaked filter-paper, the 

 contractions of those muscles which carry the tenta- 

 cles to the mouth are not produced. The tentacles 

 remain relaxed or relax still more under the stimulus, 

 and this fact, together with the ciliary movement, 

 causes the paper wad to fall off. 



2. It is said that the nerve-elements are much more 

 numerous in the vicinity of the mouth than in any other 

 part of the animal. One might think that this con- 

 centration of nerve-elements determined the reflex 

 mechanism for these reactions. For this reason, I 

 have made use of results obtained while carrying 

 on investigations concerning heteromorphosis. I had 

 found that in an Actinian of the Mediterranean, 



