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THE AMERICAN NATURALIST [Vol. XL 



wet and sleet at time of birth; (d) bulls unable to protect herds;, 

 (e) cows unable to protect young from Carnivora through starved 

 condition, or abandoning them when attacked by wolves; (/) 

 enfeebled and unprotected condition of quadrupeds favorable to 

 increased food supply and consequent multiplication of cursorial 

 and other Carnivora, especially CanidjB and Felidse. 



These zoological observations are to a certain extent borne out 

 in paleontology by Leith Adams' {British Fossil Elephants, 1879, 

 part 2, p. 98) observations of the exceptionally large number of 

 milk teeth of elephants found in certain Pleistocene deposits, 

 which appears to indicate a high mortality of the young. 



Temperature Control of Fertility and Reproduction. — Merriam*^ 

 has directed attention to one of the physiological effects of a lower- 

 ing of temperature, namely, its influence upon diminished or 

 increased fertility and the rate of reproduction in what he has 

 called the 'law of temperature control'. This he has stated as 

 follows : temperature by controlling reproduction predetermines the 

 possibilities of distribution; it fixes the limits beyond which species, 

 cannot pass; it defines l)road transcontinental barriers within 

 which certain forms nuiy thrive if other conditions permit, but 

 outside of which they cannot exist, l)e the other conditions never 

 so favorable, (because the sexes are not fertile). 



(1) Temperaiure. In discussing how species are checked in 

 their efforts to overrun the earth Merriam points out that more 



imj)<)rtaiit than humidity. First, in 1.S92, this author attempte<l 

 to show [Prnc. Biol. Sue. Wa.shitujtnu , v,l. 7, Ajml, 1S92, pp. 

 45, 40) that the distribution of terrestrial animals is governed less 

 by the yearly isotherm or mean annual temperature than by the 

 total rather than the mean temperature (hu'ing the period of repro- 

 durtivr a'-tixity and of L-rowth ^H.>h'MTnrH^ Thi. reproductive 



year, and uithin'thr \r<-ti. ( in lr a-.-l .Mnnnir-, !ZZZL 



