. Carnegie Institution of Washington publication. i8 Papers from the Marine Biological Laboratory at Tortugas. rapidly as it does on cooling; the case being in general similar to that of Cassiopea xamachana, where the rate of decline upon heating is about 8 times as rapid as in cooling. Hitherto we have considered only tropical forms or animals living in the tropics, and in these we see that a definite temperature of maximum activity is well shown in their temperature reactions. Thus for C. xama- chana the optimum is about 33° C, for ° to °, (or Aurellia aurita 29°, for the
. Carnegie Institution of Washington publication. i8 Papers from the Marine Biological Laboratory at Tortugas. rapidly as it does on cooling; the case being in general similar to that of Cassiopea xamachana, where the rate of decline upon heating is about 8 times as rapid as in cooling. Hitherto we have considered only tropical forms or animals living in the tropics, and in these we see that a definite temperature of maximum activity is well shown in their temperature reactions. Thus for C. xama- chana the optimum is about 33° C, for ° to °, (or Aurellia aurita 29°, for the movements of the branchial arms of Lepas fascicularis it is about 32° C, and for the reef corals it ranges between 30° and ° C. Thus the optimum temperature is very close to the usual temperature of the sea-water itself, this being about 28° to 31° in summer. Even a slight degree of cooling or heating beyond the optimum causes a decided falling- off in rate. A very different picture is presented by the arctic scyphomedusa Cyanea arctica, from Halifax, Nova Scotia, in September, for here the optimum. A-' 0' 10 15" 20" Degrees Centigrade Fig. 8. 25 C 30° 35° T temperature ranges from about 2° to 21° C, the animal's rate of pulsation increasing only slightly as the temperature rises, and with an ill-defined maximum at about 19° C. Upon cooling below 2° C, the medusa pulsates until the ice imprisons it, although its rate declines rapidly. Similarly, if we heat it above 21° C. the rate declines at about the same rate as it does upon cooling from 2° C. All movements cease at about 27° C. The same general conditions are also shown by Aurellia aurita from the cold waters of Nova Scotia, in marked contrast with its behavior at Tor- tugas. For example, at Halifax, Nova Scotia, in September, when the harbor water is about 14° C, the optimum temperature for Aurellia is anywhere from 2° to 18° C. and it ceases to pulsate at —° and at ° Pleas
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