MONOGRAPH OF THE EXISTING CBINOIDS. 689 



RESPONSES TO CHANGES IN SALINITY. 



Experimenting with the common comatulids at Maer Island, Torres Strait, 

 Dr. H. L. Clark was unable to obtain any response to the addition of rain water 

 to the sea water in the aquaria, even when the rain water was poured directly upon 

 the disk of the crinoid. 



The transfer of a comatulid from sea water directly to rain water met with 

 marked response and violent movements, but as long as the water in the tank was 

 predominantly salt there was no visible response to the addition of rain water. 



Increase in the amount of the salt content seemed to be a matter of equal 

 indifference. 



Regarding Tropiometra picta at Buccoo Bay, Tobago, Doctor Clark says that 

 experiments to determine whether Tropiometra is sensitive to changes in the salinity 

 of the water in which it lives gave very interesting results. 



Two individuals were placed in an aquarium containing 5 liters of ordinary 

 sea water, and two specimens of similar size and appearance were placed in another 

 aquarium containing 5 liters of 90 per cent sea water (that is, 4.5 liters of sea 

 water with 500 cc. of rain water added). 



After 12 hours all were normal, and one could not tell from the responses to 

 mechanical stimuli which were in the diluted sea water. 



Similar experiments were tried with water only 80 per cent and 75 per cent 

 sea water. 



Such water extracted color from the comatulids and after 12 hours was dis- 

 tinctly yellow, yet the animals survived and responded to the transfer to normal 

 sea water by distinct arm movements. 



Experiments were then made to see how concentrated a sea water could be 

 survived. 



Two specimens, one dark colored and one yellow and purple, survived, with no 

 apparent injury, 12 hours in only 2 liters of water 10 per cent more saline than nor- 

 mal. The brightly colored one was more active after the experiment than the other, 

 which was not what he had expected in view of the greater evaporation in the 

 natural habitat of the dark individual. 



A similar experiment with water 20 per cent more saline than normal was tried. 



A brightly colored individual was still alive after three hours; it was then 

 transferred to normal sea water and lived overnight. 



A dark-colored specimen was still alive after four and a half hours, but 

 although it was then transferred to normal sea water, it failed to revive. 



RESPONSE TO LIGHT. 



Perrier, speaking of Antedon Mftda at Roscoff, noted that the animals, while 

 accommodating themselves perfectly to daylight, do not like the direct rays of the 

 sun. When these become strong they roll up their arms, and if the exposure is 

 too prolonged, or if it is repeated too often, the arms are detached one by one and 

 fall to the bottom of the basin, and the animal soon dies. 



