118 Papers from the Department of Marine Biology. 



ulid's inertness it was impossible to determine the optimum tempera- 

 ture. In water of 33° reactions were not consistently different from 

 what they were at 25° ; nevertheless individuals in water at 33° assumed 

 a somewhat wilted appearance after a time, which was not the case 

 in water at 28° and lower. Healthy individuals gave no response to 

 a sudden change of 2°, but there was generally an evident reaction to 

 an abrupt change of 5°. 



REACTIONS TO SALINITY. 



Experiments to determine whether Tropiometra is sensitive to 

 changes in the saUnity of the water in which it lives gave very inter- 

 esting results. Two individuals were placed in an aquarium con- 

 taining 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 {i. e., 4.5 Uters of sea-water plus 

 500 c.c. of rain-water). 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 comatuUds and after 12 hours was distinctly yellow, yet the 

 tropiometras 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 saUne than normal. The brightly colored 

 one was more active after the experiment than the other, which was 

 not what I had expected in view of the greater evaporation in the 

 natural habitat of the dark specimen. A similar experiment with 

 water 20 per cent more saline than normal was tried. A brightly 

 colored individual was still alive after 3 hours; it was then transferred 

 to normal sea-water and lived over night. A dark-colored specimen 

 was still aUve after 4| hours, but although it was then transferred to 

 normal sea-water, it failed to revive. These experiments show a sur- 

 prising indifference on the part of Tropiometra to the salinity of the 

 water in which it Uves. 



REACTIONS TO CERTAIN CHEMICALS. 



Although no experiments were made to test the reactions to chemi- 

 cals, it may be worth while to record the observations made in other 

 connections. Indifference to the amount of CO2 in the water was 

 noticeable, particularly in view of the sensitiveness of Torres Strait 

 comatulids to that substance. As already stated, 2 specimens lived 

 over night in only 2 liters of sea-water, apparently without discomfort, 

 and 4 or 5 specimens were often kept over night in aquaria with not 



