256 Influence of environment on animals 
Ill Tae INFLUENCE oF TEMPERATURE. 
(a) The influence of temperature upon the density of pelagic 
organisms and the duration of life. 
It has often been noticed by explorers who have had a chance to 
compare the faunas in different climates that in polar seas such 
species as thrive at all in those regions occur, as a rule, in much 
greater density than they do in the moderate or warmer regions 
of the ocean. This refers to those members of the fauna which live 
at or near the surface, since they alone lend themselves to a 
statistical comparison. In his account of the Valdivia expedition, 
Chun’ calls especial attention to this quantitative difference in the 
surface fauna and flora of different regions. “In the icy water of 
the Antarctic, the temperature of which is below 0° C., we find an 
astonishingly rich animal and plant life. The same condition with 
which we are familiar in the Arctic seas is repeated here, namely, that 
the quantity of plankton material exceeds that of the temperate and 
warm seas.” And again, in regard to the pelagic fauna in the region 
of the Kerguelen Islands, he states: “The ocean is alive with 
transparent jelly fish, Ctenophores (Bolina and Callianira) and of 
Siphonophore colonies of the genus Agalma.” 
The paradoxical character of this general observation lies in the 
fact that a low temperature retards development, and hence should 
be expected to have the opposite effect from that mentioned by 
Chun. Recent investigations have led to the result that life-pheno- 
mena are affected by temperature in the same sense as the velocity 
of chemical reactions. In the case of the latter van’t Hoff had 
shown that a decrease in temperature by 10 degrees reduces their 
velocity to one half or less, and the same has been found for the 
influence of temperature on the velocity of physiological processes. 
Thus Snyder and T. B. Robertson found that the rate of heartbeat in 
the tortoise and in Daphnia is reduced to about one-half if the 
temperature is lowered 10°C., and Maxwell, Keith Lucas, and 
Snyder found the same influence of temperature for the rate with 
which an impulse travels in the nerve. Peter observed that the 
rate of development in a sea-urchin’s egg is reduced to less than one- 
half if the temperature (within certain limits) is reduced by 10 
degrees. The same effect of temperature upon the rate of develop- 
ment holds for the egg of the frog, as Cohen and Peter calculated 
from the experiments of O. Hertwig. The writer found the same 
temperature-coefficient for the rate of maturation of the egg of a 
mollusc (Lottia). 
1 Chun, Aus den Tiefen des Weltmeeres, p. 225, Jena, 1903. 
