222 BEHAVIOR OF THE LOWER ORGANISMS 



certain active movements which assist in procuring food. In most sea 

 anemones light stimulation of the tentacles, however produced, causes 

 these organs to wave back and forth, just as happens in medusae ; this 

 increases the chances of coming in contact with food. In Sagartia, ac- 

 cording to Torrey, the presence of food near one side of the animal, 

 resulting in weak chemical stimulation, gives rise to more definite move- 

 ments. Part of the tentacles bend toward the food, contracting on the 

 side most strongly stimulated, while others bend toward the mouth. The 

 animal may at times bend its body toward the food, thus securing it. 

 The tendency of the tentacles to bend toward the mouth, as if carrying 

 food, when stimulated in almost any way, is very striking in many 

 ccelenterates. In Sagartia the tentacles when touched bend first toward 

 the side stimulated, then toward the mouth. In the hydroid Cory- 

 morpha, according to Torrey (1904 a), the tentacles when thus stimulated 

 bend only toward the mouth. This bending toward the mouth of course 

 serves the function of carrying food, and it seems to have become the 

 reaction to all sorts of stimuli, on the chance, as it were, that it will serve 

 this function, in the given case. The plan of the behavior is that of 

 trial of a reaction that is beneficial under most circumstances. 



The Taking of Food. — In the actual taking of food the behavior 

 varies greatly in different sea anemones. In some species ciliary move- 

 ment plays the chief part in the process, 1 though assisted by muscular 

 contractions. In others, bodily movements brought about by muscles 

 are the main factors. Two or three examples will illustrate the principal 

 variations in this matter. 



The common Metridium marginatum of the east coast of the United 

 States is an example of the species in which ciliary movement is perhaps 

 the chief agent in food-taking. Under usual conditions the tentacles are 

 pointed away from the mouth, and are covered with cilia, which beat 

 toward the tip of the tentacle. Thus small particles falling on the ten- 

 tacles are carried outward by the cilia and removed from the animal. 

 But if the particle is something fit for food, the behavior is changed. 

 When a bit of crab's flesh is dropped among the tentacles, they contract 

 on the side touched, thus grasping the flesh. They then bend inward, 

 arching over with tips toward the mouth. The cilia, continuing to strike 

 toward the tip, now of course carry the food toward the mouth instead 

 of away from it. In time the meat drops from the tip of the tentacles 

 into or near the mouth. 



The inner surface of the oesophagus, or tube into which the mouth 

 leads, is covered with cilia, which beat outward (save in the two grooves 

 at the angles, known as the siphonoglyphes). They thus bear outward 



1 For details regarding this for many different species, see Carlgren, 1905. 



