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Reactions to Temperature

water, 33 and 28

REACTIONS TO TEMPERATURE.

While it was not feasible to produce really low temperatures, water in the tank fell to 22° C. during the night. At this temperature Tropiometra showed no signs of discomfort or stimulation. When the water was gradually raised to 33° or 34°, responses to mechanical stimulation were normal. At 35.5° two of the four specimens tested were quite unresponsive, but the other two gave normal responses by arm-movements. One continued to respond at 36.5°, but at 37.5° was inert. After a few moments at that temperature the four speci mens were placed in normal sea-water at 28°, but none recovered. Individuals taken from water at 28° and placed in that at 33° con tinued to give responses with the arms. At 34°, however, the arms were quiescent, but the pinnules responded. Complete recovery of these specimens resulted when after a few moments they were again placed in water at 28°. Individuals placed in water at 36° gave no responses and failed to recover; they became quite rigid. These

experiments show that as compared with the comatulids of Torres Strait, Tropiometra has a surprisingly large temperature range. This is quite in keeping with their habitat in Buccoo Bay, for while the water there probably never falls below 22° C., there is no doubt that at the lowest tides it rises in the shallows to 32° and possibly to 34°. Even should it on rare occasions exceed this figure for a short time, it is evident that Tropiometra would easily survive. Owing to the comat 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°.