MONOGRAPH OF THE EXISTING CRINOIDS. 691 



Regarding Tropiometra picta as he found it at Buccoo Bay, Tobago, Dr. H. L. 

 Clark says that its remarkable habitat naturally suggested that in its reactions to 

 light it would be positively phototactic. 



A tank 6 feet long, a foot wide, and 8 inches deep, having the bottom covered 

 with broken coral and stones, was used for the experiments. It was placed near 

 high- water mark on the beach, in the sun, and two boards, 5 or 6 inches wide, were 

 laid across it, giving shaded areas. One end was made quite dark by covering with 

 a broad piece of board and burying it in the sand. 



Numerous individuals of Tropiometra picta were tested in this tank on many 

 different occasions and under diverse conditions of temperature. The results were 

 surprisingly unsatisfactory. No individual showed any decided reaction to light, 

 and none sought the darkness. In most cases, when the specimen was fresh from 

 Buccoo Bay, if placed in a shaded area it remained there; if placed in the sun 

 close to a shaded area it moved into the shade, but if the board were then removed 

 it made no effort to move out of the sun : if placed in the sun some, inches from 

 the shade it remained quietly in the light. 



Generally the individuals were placed upside down in the tank, so that the 

 process of righting might serve to initiate movement. But, although they righted 

 themselves promptly, they rarely wandered more than a few inches thereafter. 

 If placed in the tank right side up they were usually content to remain where put, 

 regardless of whether it was in sun or shade. 



Experiments were made particularly to see whether the brightly colored speci- 

 mens from under rocks reacted differently from the dark individuals from Buccoo 

 Bay, but no constant differences could be detected. Brightly colored examples 

 seemed to be a little less hardy and became sluggish and inert in the tank more 

 quickly than the dark ones, but the difference was not striking. 



The final conclusion reached, as a result of all the experiments and obser- 

 vations, was that Tropiometra picta at Tobago is slightly negatively phototactic 

 but that other factors in the environment at Buccoo Bay neutralize this tendency 

 almost or quite completely, while on Buccoo Reef it is for some reason strengthened. 



While the Albatross was anchored off Sulu a small specimen of Dorometra 

 nana, about half the adult size, was captured which had been attracted to and was 

 swimming about a submerged electric light. 



RESPONSE TO HEAT. 



All of the information on this subject we owe to Dr. H. L. Clark, from whose 

 accounts the following is taken : 



Observations at Maer Island, Torres Strait. As ice was not obtainable at 

 Maer, and it was difficult to lower the temperature to any considerable degree, his 

 only experiments with regard to the response of comatulids to temperature changes 

 dealt with the effect of raised temperatures. 



An alcohol stove placed under one end of the tank made it possible to raise 

 the water just over the flame several degrees without appreciably affecting the 

 temperature of the other end for nearly an hour. 



