FEEDING REACTIONS IN CORAL POLYPS. 433 



On the other hand in less favorable circumstances the whole of the 

 imported algae together with those already present in the tissues 

 of the sponges are digested. 



INFECTION OF COLORLESS POLYPS WITH ZOOXANTHELL^:. 



In my experiments I kept the colonies ot white polyps separated 

 from those with brown polyps (brown on account of their 

 zooxanthellae). As the white polyps did not become infected dur- 

 ing a month's time there is little evidence that infection occurs 

 through free zooxanthellae in the sea water. In a number of 

 polyps I produced an artificial infection with zooxanthellae by 

 feeding them with portions of the soft parts of dark brown polyps. 

 Especially those parts of the brown polyps which contained a 

 multitude of these algae (the tentacles and the oral disk) were used 

 for this experiment. The tissues w T ere torn to minute pieces and 

 thoroughly mixed with pounded crab meat. It was necessary to 

 add meat to the tissue preparations for otherwise the polyps 

 refused to feed upon it. 



Soon after feeding a number of zooxanthellae had detached from 

 the crab meat and were floating free in the gastric cavity of the 

 polyps and sometimes even the tentacles assumed a light brown 

 color by the algae which had penetrated into their cavity. A 

 large part of the zooxanthellae from the feeding mixture were 

 ingested together with the meat by the mesenterial filaments. 

 After three days the digestive region of these organs was crowded 

 with algae. Some of these were already partially digested, for 

 white spots had appeared in the originally evenly yellow colored 

 interior. 



Some of the cells which a very short time after the feeding are 

 found in the cavity of the tentacles penetrate into the entoderm 

 cells of these organs. Here they quickly multiply by division 

 into two halves. The following numbers clearly illustrate the 

 quick increase in number of the zooxanthellae in the tentacles of 

 recently infected polyps. In one polyp on the day after the 

 infection a cut-off top of a tentacle contained 6 symbiotic algae, 

 three days after the infection a top of a tentacle of the same length 

 contained 23. For another polyp the number of zooxanthellae in 

 the entoderm of different distal parts of tentacles of about equal 



