FEEDING REACTIONS IN CORAL POLYPS. 415 



To study the normal feeding reactions I therefore fed the polyps 

 with planktonic organisms, chiefly copepods and larvae of decapod 

 crustaceans. It proved to be an advantage when the food was 

 colored, then it could be seen through the transparent tissues 

 when it was captured and swallowed. For this reason I used the 

 method employed by Fischel (1908) for daphnids and copepods 

 of fresh water. To the sea-water which contained the animals a 

 few drops of a solution of neutral red were added by means of 

 which the water obtained a light yellow color. The copepods 

 and other organisms now absorbed the coloring matter and 

 gradually acquired a bright red hue. Especially the different 

 parts of the intestinal tract absorbed a great quantity of neutral 

 red, but also immediately beneath the skeleton and in the ap- 

 pendages the coloring matter was stored. These colored cope- 

 pods and larvae of decapods are as readily taken by the polyps as 

 colorless ones. 



When some of these colored planktonic organisms are put into a 

 small glass containing a colony of Astrangia with expanded polyps 

 the capture of these animals may be easily observed. Every now 

 and then one of the animals comes into contact with a tentacle of 

 a polyp. Smaller copepods then as a rule are immediately 

 captured, they seem to stick to the tentacle, undoubtedly by 

 their being paralyzed by nematocysts. The tentacle then 

 suddenly contracts more or less and bends over the oral disk in 

 the direction of the mouth. The prey, however, is not brought 

 directly to the mouth. The latter, with the central part of the 

 oral disk, slowly increases in height as a conical protusion and this 

 expanded part gradually moves in the direction of the prey. At 

 last the tentacle with the copepod comes into contact with the 

 mouth, the tentacle releases the prey and bends back to its 

 original place. The captured copepod slowly slides down through 

 the stomodaeum into the gastric cavity, undoubtedly by ciliary 

 action, and the mouth returns to the central part of the disk. 



Larger copepods and larvae of decapods, however, are not so 

 easily captured. When they touch a tentacle they often swim 

 away with a sudden jerk, the attack of the nematocysts seeming 

 insufficient to paralyze them. Only when these animals bump 

 heavily against a tentacle they are immediately caught. Their 



