116 Papers from the Department of Marine Biology. 



crannies in the rock, but generally the movement was over the surface 

 of the rock to its margin and thence down into the shade of its now 

 lower side. The movement was never spasmodic or hurried, but unless 

 interfered with was very steady and soon accomplished its purpose. 

 It is difficult to see how this invariable habit can be interpreted as 

 anything else than a response to light as a stimulus. Since the rock 

 might be 3 feet under water, no change of temperature could possibly 

 have caused the movement ; it is conceivable, however, that the change 

 of position due to the overturning of the rock was the effective stimulus. 

 But the theory that change of position is the determining factor seems 

 to be eliminated by the facts that among the living corals comatulids 

 occur with the oral surface either up, down, or lateral, and that when 

 the coral around them is broken away with a hammer, exposing them 

 to strong light but not disturbing their position, their movements are 

 also away from the lighted area into the shadow. 



Experiments in the laboratory were not altogether satisfactory, so 

 much individual difference was shown. As a rule, if a comatulid was 

 placed at the middle of the tank, one end of which was covered over, 

 while the other end was in sunlight, movement to the shaded end 

 almost always was the first result. Often, however, the animal did 

 not remain there, but moved about restlessly, even to the brightly 

 illuminated end. In such cases it is a fair inference that the absence 

 of suitable surface for attachment was the cause of the restlessness. 

 More consistent results followed when direct sunlight was allowed to 

 fall on comatulids which had been in the shade. With scarcely an 

 exception, they moved out of the brightly lighted area. Experiments 

 with artificial light were entirely negative, presumably because of the 

 weakness of the stimulus, nothing better than an ordinary kerosene 

 lamp being available. No specific differences were noted with reference 

 to light reactions, all the species watched giving the same results. 

 Bright sunlight thrown abruptly on a comatulid lying in shadow often 

 produced immediate and sometimes more or less spasmodic closing of 

 the arms over the oral surface of the disk, as though that part of the 

 animal were most sensitive to the stimulus. In confirmation of the 

 view that the disk is more sensitive to light than the arms is the fact 

 that in their natural habitat the crinoids often extended the arms out 

 into the light, while the body itself was in heavy shadow. Indeed, all 

 along the southwestern reef, on the brightest days, they were to be 

 seen in such a position. 



RESPONSE TO HEAT. 



As ice was not obtainable at Mae'r and it was difficult to lower the 

 temperature of any large amount of water to any considerable degree, 

 my only experiments with regard to the response of comatulids to 

 temperature changes dealt with the effect of raised temperatures or, 



