FEEDING REACTIONS IN CORAL POLYPS. 409 



An account of the chief peculiarities of Astrangia dance, ac- 

 companied by figures, some of which represent the polyps in an 

 expanded form, are found in the publications of Mrs. and Mr. 

 Agassiz (1865) and of Dana (1890). Verrill and Smith (1874) 

 also give a short description of the polyps of this species. They 

 state that the animals are white and that the polyps in expansion 

 rise high above the skeleton. These authors also note that the 

 polyps will feed readily upon fragments of molluscs or crustaceans. 



In the literature on the coral Astrangia I have not found any 

 remark on its symbiosis with zooxanthellae. In the greater part 

 of the colonies of this species found in the Woods Hole region all 

 polyps are completely free of zooxanthellae. This was invariably 

 the case in the specimens which I obtained from the piles of the 

 wharf at Woods Hole, in those dredged in the harbour between 

 Woods Hole and Nonamesset Island and in those dredged to the 

 southeast of Nonamesset Island from about 8 fathoms. On the 

 other hand the specimens dredged to the southwest of Falmouth 

 (south of the oyster-pond) were always more or less infected with 

 zooxanthellae. Some of the polyps of this locality had a dark 

 brown color owing to the multitude of yellow algse occurring in 

 their tissues, others had various lighter shades of brown or were 

 almost white, but a microscopical examination of a part of their 

 tentacles or oral disk proved that they invariably contained 

 zooxanthellae. It is a strange fact that this symbiosis of the polyp 

 with yellow cells in the Woods Hole region is restricted only to the 

 colonies found in certain smaller localities. 



The polyps which are not infected by zooxanthellae are quite 

 colorless and these are therefore especially fit for the study of the 

 feeding reactions as foreign bodies can be seen through the trans- 

 parent tissues of the animals. Usually the skeleton has a greenish 

 or light-red color, which is due to the occurrence of algae living in 

 the skeleton. Then at first sight the polyps sometimes seem to 

 have a pink or greenish hue by the transparency of their tissues. 

 Probably these red or green-colored algae are only different stages 

 in the development of one species as their microscopical structure 

 is very much alike. As yet I have no positive evidence that they 

 belong to one of the forms described by Duerden (1905). In 

 some colonies a compact mass of algal matter is obtained after 



