FEEDING REACTIONS IN CORAL POLYPS. 435 



period in all probability the digestion takes place. There is 

 sufficient evidence that besides intracellular digestion a secretion 

 of a digestive fluid (a trypsin-like enzyme) occurs. 



In the polyps of Astrangia which contain zooxanthellae in their 

 entoderm these unicellular algae furnish a part of the normal food 

 of the polyps: a quantity of these algae are digested in the mesen- 

 terial filaments. 



Polyps of Astrangia without zooxanthellae can be easily infected 

 with these algae by feeding them with crab meat mixed with parts 

 of the tissues of strongly infected polyps. 



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