434 H - BOSCHMA. 



size was : I day after the feeding 4 and 5 ; 2 days after the feeding 

 9, 16, 2, 21 and 12. In a third polyp the number of the algae in 

 tentacular extremities of approximately equal size was: 3 days 

 after the feeding 30, 28, 22, 17 and 27; 9 days after the feeding 

 72 and 53. Consequently the zooxanthellae in the entoderm cells 

 after the infection gradually had increased in number, though the 

 change in color of the polyp could not yet be observed at first 

 sight, for in moderately brown polyps extremities of tentacles of 

 the same size as those cut-off in my experiments contain far more 

 than 1,000 zooxanthellae. 



After the feeding with the mixture of crab meat and zooxan- 

 thellae the infected polyps were fed several times with crab meat 

 to keep them in a well-fed state. In hungry polyps the zooxan- 

 thellae perhaps might divide less rapidly. 



I could not continue these experiments of infection for more 

 than 9 days, but I am convinced that in this way a white polyp 

 may be changed into a brown one crowded with zooxanthellae in 

 the entoderm cells. Probably in nature the infection may take 

 place (though rarely) in a similar way. When the polyps capture 

 an animal which contains zooxanthellae some of these may find 

 their way to the entoderm of the tentacles or the oral disk. 

 After division these cells may infect the neighboring cells and at 

 last the whole of the entoderm of the colony. This manner of 

 infection in all probability only rarely occurs. As in other coral 

 polyps with symbiotic algae the greater part of the infected polyps 

 of Astrangia undoubtedly have originated from planulae which 

 already obtained the symbiotic algae before hatching. This view 

 is supported by the fact that all the infected polyps of the Woods 

 Hole region were found in a comparatively restricted locality. 



SUMMARY. 



The feeding reactions of Astrangia in general consist ot four 

 actions: 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. 



The reaction of the food-vacuoles in the digestive region of the 

 mesenterial filaments immediately after the feeding is acid ; after 

 about two days the reaction changes to alkaline. In this alkaline 



