BEHAVIOR OF CCELENTERATA 223 



any indifferent particles which may fall in the oesophagus. But when a 

 piece of meat is dropped into the mouth, the cilia at once reverse, now 

 beating inward. They thus carry the food into the digestive cavity of 

 the animal. 



Meanwhile, the muscles surrounding the mouth, and those of the 

 oesophageal tube, contract in such a way as to produce swallowing move- 

 ments, which aid in ingesting the food. These swallowing movements 

 may begin while the food is still held by the tentacles, showing that the 

 stimulation from the food has been transmitted. 



In Aiptasia annulata there are cilia which act in the same manner 

 as in Metridium, but the chief role in food-taking is played by move- 

 ments of the tentacles and oesophagus. If a small object comes in con- 

 tact with a tentacle, it adheres to the surface, and the tentacle contracts 

 strongly, the entire animal usually contracting at the same time. Then 

 the tentacle bends over and places the food with considerable precision 

 on the mouth. The adjacent tentacles likewise bend over and are ap- 

 plied to the food body, holding it down against the mouth. The latter 

 then opens, the lips seizing the food, while the tentacles may release it 

 and bend away. The swallowing of the food is mainly due to the activi- 

 ties of the lips and oesophagus. In this animal a bit of food may be 

 completely enclosed within ten seconds of the time it touches a tentacle. 



In the large sea anemone Stoichactis helianthus, cilia seem to play 

 no part in the taking of food. In this animal the disk may be 10 to 

 15 cm. in diameter. If a piece of crab meat is placed on the disk 

 of a hungry specimen, the tentacles immediately surrounding it be- 

 gin suddenly to wave back and forth. This movement stops for a 

 few seconds, then begins again. All the tentacles that come in contact 

 with the food bend over against it and shrink, so as to hold it down 

 against the disk. Now that portion of the disk bearing the food begins 

 to sink inward, the mouth begins to open, and the walls of the oesopha- 

 gus protrude from the mouth as large bladderlike lobes. The region 

 between the mouth and the food contracts, the tentacles which it bears 

 collapsing and almost completely effacing themselves. By this con- 

 traction the mouth and food are caused to approach each other, the 

 intervening region almost disappearing. The oesophageal lobes in- 

 crease in size, becoming 3 or 4 cm. long and half as thick; they 

 extend toward the food, finally reaching it. The mouth may, in the 

 way described, be transferred from the centre of a disk 10 cm. in 

 diameter to within 1 cm. of the edge. Now the oesophageal lobes 

 extend over the food, while the tentacles progressively withdraw from 

 it, till the food is lying on the contracted part of the disk, completely 

 covered by the oesophageal lobes. Now that part of the disk below the 



