l6o REPORTS ON INVESTIGATIONS AND PROJECTS. 



The cilia of Mceandra areolata, external to a line corresponding nearly 

 with the top of the septal arch, appear, as a rule, to beat outward, while 

 those within this line appear usually to beat inward. The entire ciliary ap- 

 paratus, however, may be made to operate in directions almost at the will of 

 the experimenter. By stimulating the specimen with food the cilia from the 

 lowest margin of the edge-zone may be made to drive the food toward the 

 mouths, while if sand grains are used the cilia of the oral disk will drive the 

 undesirable material toward the periphery. 



In conducting the experiments to ascertain the responses to food stimuli, 

 both solid and liquid food was used. The solid food consisted of bits of 

 crab-meat {Ocypoda arenaria) or bits of minnows, and the liquid food of 

 beef -juice. The reactions to these substances were in some particulars simi- 

 lar, in others different. The specimens to be experimented with were placed 

 in glass dishes, deep enough to submerge the specimen to a depth of half an 

 inch or more, and the experiments were conducted on a well-lighted shelf or 

 table, but not in direct sunlight. 



When a piece of solid food is placed on the oral disk of a specimen, 

 under the conditions indicated, the polyps begin immediately to distend, the 

 stimulus passing from polyp to polyp, and if the specimens be not too large 

 the entire colony will expand. Very nearly any specimen of coral may be 

 induced to expand in ordinary shaded light, shielded from direct sunlight, by 

 placing a piece of solid food on its surface. (I have seen a specimen of 

 Mceandra clivosa in its natural habitat, with its polyps fully distended in 

 strong sunlight.) When a piece of solid food is offered to a tentacle it is 

 seized and passed downward to a mouth which opens to receive it. Then 

 the upper edges of the edge-zone are brought together, forming an arch over 

 the mouth. After the food particle has been completely swallowed the edge- 

 zone margins usually separate, exposing the oral surface. An experiment, 

 repeated several times, was to place a piece of Ocypoda meat in a depression 

 on the top of a colline, in the most inaccessible place on the upper surface of 

 the specimen. All tentacles near the bit of food were directed toward it, and 

 it soon moved upward over the septal arch and was captured by a tentacle. 

 Through the combined action of the cilia and mucus, food particles can be 

 carried to a mouth from any part of the outer surface of the soft tissues. 



Carmine particles were mixed with the beef- juice when using this ma- 

 terial in experiments. The function and operation of the cilia and mucus 

 are the same in response to the stimulation of liquid food as to that of solid 

 food, but the tentacles usually remain inactive. The mucus with the entan- 

 gled carmine grains moved toward the mouths, in some instances being 

 drawn as colored streamers into the mouths, which open very widely. Occa- 

 sionally a tentacle may grasp a mucus thread, while sometimes the tentacles 

 may be entirely retracted. After the liquid food is within the margins of the 

 edge-zone, the edges contract over the oral apertures and, after the swallow- 

 ing is complete, retreat, exposing the oral disk. 



After satiation the direction of the ciliary motion reverses, so that what 

 was taken as food is carried to the periphery and dropped off, and the ten- 

 tacles will not seize food particles. 



The preceding remarks give a summary of the principal reactions to food 

 of Mceandra areolata. In other species, one of which is Orbicella cavernosa, 

 the mesenterial filaments can, while protruded through the column wall, not 

 only catch food, but can digest the food without taking it into the gastric 

 cavity. 



