THE INFLUENCE OF PHYSICAL FACTORS 101 



THE POSSIBILITY OF ACCLIMATIZATION IN COLD-BLOODED ANIMALS. 



The temperatures at which cold-blooded animals are able to live and 

 to be active range from 2 to 3 below o in the case of arctic marine 

 animals, of which many living at great depths are never exposed to 

 temperatures above o , 1 to temperatures about 40 in the case of 

 tropical forms, and even above 40 (probably up to 60) in a few forms 

 living in hot springs. Instances are known in which nearly related 

 forms or even animals belonging to the same species inhabit localities 

 with extremely different temperatures 2 (Davenport and Castle, 1895). 

 It would be interesting to compare the respiratory exchange in such 

 cases, because it would appear unlikely from a teleological point of view 

 that it should differ so much as would be ordinarily implied from the 

 temperature difference. One would expect that animals living at a 

 very low temperature should show a relatively high standard meta- 

 bolism at that temperature compared with others living normally at a 

 high temperature. Extremely little has been done, however, in this 

 direction. 



Montuori [1907] has attempted to acclimatize different animals 

 (CarcinuS) Amphioxus, several fishes) by heating the water in the 

 aquaria in which they were kept slowly (during six to seven days) from 

 n-i3 to 27-3O at which latter temperature the animals then re- 

 mained. He compared the respiratory exchange after two days at the 

 high temperature with that at the low, and found that it had not in- 

 creased but actually decreased to about one half or less ! This result 

 is so improbable, however, that it appears almost certain that the 

 animals were no longer normal or that some very serious error must 

 have crept into the determinations. 



Krehl and Soetbeer [1899] have compared the heat production of 

 animals from temperate climates (Lacerta, Rana] with tropical forms 

 (Alligator^ Uromastix) and found higher figures for the former than for 

 the latter at identical temperatures. Their results are complicated, how- 

 ever, by the two facts that their tropical animals were much larger and 



1 According to Ad. Jensen, The Selachians of Greenland, Mindeskrift for J. Steenstrup, 

 Copenhagen, 1914, a certain species of ray (Raja hyperborea) is never found outside those 

 areas in the Davis Strait and North Atlantic where the temperature of the bottom water in 

 which it lives is below o. The boundary line between these areas and those in which the 

 water is warmer (+ i to +3) is in several places very sharp and Raja hyperborea has been 

 caught just up to that line. 



a A species of Ephydra (a fly) lives as larva both in brackish water at certain points on 

 the Danish coast and in a hot spring in Iceland at a temperature of about 50. 



