418 H. BOSCHMA. 



causing any injury to the polyp. I used this method to make out 

 whether or not zooxanthellae were present in the gastric cavity of 

 polyps the tissues of which contained these unicellular algae. 



Small pieces of filter paper rarely induce the polyps of Astrangia 

 to feeding reactions. To avoid the absorption of organic sub- 

 stances (cf. Parker, 1905) the pieces of paper were not touched 

 with the hands, but they were handled by clean instruments and 

 put on the tentacles of a hungry polyp. For some time the small 

 objects remain attached to the tentacles, to which they adhere 

 more or less, but as a rule they soon fall down without causing the 

 feeding reaction. In some cases, however, a few pieces of filter 

 paper are ingested and afterwards, after about 50 minutes, 

 removed from the gastric cavity in the above described manner. 

 The difference in behavior of hungry polyps to comparatively 

 heavy objects as small pebbles and pieces of filter paper in all 

 probability is caused by the difference in weight. The heavy 

 objects give a definite mechanical stimulus which immediately 

 brings forth the feeding reaction, whilst the pieces of filter paper 

 act as indifferent objects. 



When carmine-powder soaked in seawater is distributed over 

 expanded hungry polyps large quantities are ingested. There is 

 no evidence of ciliary action on the oral disk, probably cilia are 

 not to be found here. Soon after the carmine has dropped on the 

 oral disk it is imbedded in mucus and large strains of this mixture 

 of mucus and carmine can be seen gliding down the stomodaeum 

 through the inward beating of the cilia of the latter. Often a 

 quantity of carmine is ingested by the cells of the mesenterial 

 filaments, but it also occurs, especially when large quantities of 

 carmine are present in the gastric cavity, that clumps of carmine 

 mixed with mucus are removed from this cavity as non-nutrient 

 particles. 



The feeding reactions of Astrangia in general therefore consist 

 chiefly of four actions of the polyps: muscular action of the 

 tentacles, muscular action of the central part of the oral disk, 

 secretion of mucus by the oral disk, and ciliary action of the 

 stomodaeum. 



