BEHAVIOR OF CCELENTERATA 227 



10. Independence and Correlation of Behavior of Different 



Parts of the Body 



There is a general agreement among those who have studied the 

 behavior of coelenterates that the different parts of the body show re- 

 markable independence in their reactions. The tentacles of the sea 

 anemones and medusae react to most stimuli in essentially the same 

 manner when cut off from the body as when attached. The isolated 

 tentacles of Gonionemus react to meat juice by contracting and twist- 

 ing, as in the usual food reaction, while to inorganic chemicals they react 

 by a straight contraction, as in the negative reaction of the medusa 

 (Yerkes, 1902 b, p. 183). In Sagartia (Torrey, 1904) and Metridium 

 (Parker, 1896) the separate tentacles react to meat juice by bending 

 toward the side which formerly looked toward the mouth. Thus 

 each tentacle must contain within itself the apparatus necessary for its 

 usual reactions. 



The fact that the tentacles have their own reactions independently of 

 the rest of the body is illustrated in a curious way in Loeb's experiment 

 on heteromorphosis in Cerianthus (Loeb, 1891). He succeeded in 

 causing tentacles to develop at one side of the animal, forming a group 

 not associated with a mouth. These tentacles reacted to food as usual, 

 seizing upon it, and bending over with it in the direction in which, 

 under normal conditions, a mouth would be found. Here it was pressed 

 down for a time, then released. 



Like the tentacles, other parts of the body may react independently. 

 Yerkes (1902 h) cut off the manubrium of Gonionemus and pinned it 

 by its base to the bottom of a dissecting dish. It now bent toward food, 

 seized upon and swallowed it, just as in the uninjured medusa. Many 

 experiments with similar results are described in the work of Romanes 

 (1885). Parker (1896) isolated a small bit of the cihated epitheUum 

 of the oesophagus of Metridium. He found that this reacted to meat 

 juice by a reversal of the ciliary stroke, just as happens in the uninjured 

 animal. In Actinia, Loeb (1891) found that if the head is cut off, the 

 lower part of the animal will take food through the oesophageal opening. 

 If the animal is cut in two, even the open lower end of the upper half 

 will take food, just as will the mouth. 



For experiments of this kind, the bell of the medusa has become, 

 through the work of Romanes (1885), a classical object. Separating 

 the margin of the bell, containing the chief portion of the nervous sys- 

 tem, from the central part, has been a favorite experiment. Romanes 

 found that in the Hydromedusas the margin continues to beat rhythmi- 

 cally, while the centre usually ceases its spontaneous movement. But 



