of the. Arctic (Ui'i (he Antitrjtic Fuuncis. '.ii)') 



different requiromeiits in rc^^aid to warmth, ami wfie tln-ic- 

 fore nble to live also in teinpeiato latitudes; sccuiuJIy, 

 because, if our latitudes enjoyed a elinmte of tropical warnitli 

 in Tertiary times, the torrid zone nui.st have had a hv|)('r- 

 tropieal climate, which would have annihilated all lite 

 within it. 



These objections cannot here be considered in detail, but 

 the n)ost important refutations of them may be brou^Hit 

 forward. 



(I) Modern biology has long since admitted that the chief 

 factor determining the distribution of plants and of cold- 

 blooded animals, and especially marine animals, is to be 

 sought for in the conditions of temperature. Other conditions 

 of life are, of course, of great influence, but they only ac- 

 centuate the state of affairs primarily brought about by the 

 temperature. Thus equality of temperature is, casleris 

 puribusj a distribution-bridge, inequality a distribution - 

 barrier. The fauna of our tropical surface-water cannot 

 sj)read from the tropics into temperate latitudes, and it is 

 contrary to our most firmly established beliefs to assume 

 that a fauna with a habit similar to that of the tropical fauna 

 of to-day, and with, in the main, the same genera, can have 

 lived in a temperate climate in Early Tertiary times. This 

 may be es))ecially illustrated by reference to the reef-corals, 

 which form such a characteristic feature of the troj)ical fauna 

 of to-day, precisely because of their invariable sensitiveness 

 to less than tropical heat. 



Great jjrobability is lent to this view by the more and 

 n)ore pronounced se[jarating-out of the Early Tertiary fauna 

 into zonally disposed faunas, which took place during the 

 Tertiary period. This point will be more fully discussed 

 later on. 



This view of the climate of the Tertiary period has been 

 strongly corroborated by the researches of Murray and Irvine, 

 according to which an abundant secretion of lime is only 

 possible in a warm climate. That lime in solution is precipi- 

 tated only to a slight extent in cold water, but in great 

 abundance in warm water, is in itself only a chemical fact ; 

 but the circumstance that the animals of the higher latitudes 

 secrete little lime, while tropical animals secrete it in abun- 

 dance, at once gives the chemical fact a physiological signi- 

 ficance. And, according to it, the formation of coral-reefs is 

 possible only in water of tro[)ical warmth. 



We believe, therefore, that no cliango in the amount of 

 warmth required by marine animals has taken [)lacc. The 

 lovers of warm water, which were unable to endure tho 



