(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 (Chun, "Aus den Tiefen des Weltmeeres", page 225, Jena, 1903.) 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 deg 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-phenomena 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 deg 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 development 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).