IV. 



The Effect of Temperature on the Distribution 



of Marine Animals. 



THE question of the influence of temperature on marine animals is 

 a comparatively old one. Twenty years ago and more it had 

 been already discussed in England and America, but even at the 

 present day it is far from being solved. On the contrary, very con- 

 flicting views prevail as to the importance of temperature on the 

 distribution of marine life. Some authors regard it as the sole 

 important factor, others do not attribute any value to it at all. This 

 diversity of opinion is less the result of a lack of facts, our store of 

 which has been greatly increased by the last years' expeditions ; but 

 it is rather to be attributed to an incorrect grouping of the facts. 

 My intention, on the present occasion, is not so much to bring for- 

 ward new data as to re-arrange those we already possess. 



The conflict of opinion may be seen in the work of two investi- 

 gators, whose particular line is geology, but who have occupied 

 themselves especially with marine biology as a territory intermediate 

 between the sciences of Zoology and Geology. I refer to Walther 

 and Heilprin. 



Walther says, at the end of a detailed argument, after 

 enumerating many facts, which are to prove the influence of 

 temperature, that the latter is not only one factor, but the exclusively 

 determining one, in comparison to which all others, like light, 

 atmospheric pressure, etc., are quite in the background. 



Heilprin, in a discussion of the fauna of the deep sea, does not 

 attribute so great an influence to temperature, and brings forward the 

 following train of argument. Reef-building corals, which flourish 

 best at 70-75° F., and which do not grow below 68°, would find this 

 temperature in many oceanic parts, even at a considerable depth, in 

 the Red Sea, for instance, even down to the bottom ; nevertheless, 

 they occur everywhere only at the surface. Conversely, the fauna of 

 the deep sea begins in the lesser depths (100 fathoms if there is a 

 bottom), and, though the temperatures are much higher there than in 

 the real abysses, the fauna is the same. The beginning of the fauna 

 of the deep sea is always to be recognised at a certain depth, which 

 is about the same in metres everywhere, but which must have a very 



