EXTINCTION OF SPECIES. 433 



dental series there, and have afforded an additional feature of 

 resemblance to the Plagiaulax. 



The foregoing are some of the more interesting illustra- 

 tions of the law, that " with extinct as with existing Mam- 

 malia, particular forms were assigned to particular provinces, 

 and that the same forms were restricted to the same pro- 

 vinces at a former geological period as they are at the 

 present day."* That period, however, was the more recent 

 tertiary one. 



In carrying back the retrospective comparison of existing 

 and extinct Mammals to those of the eocene and oolitic strata, 

 in relation to their local distribution, we obtain indications 

 of extensive changes in the relative position of sea and land 

 during these epochs, in the degree of incongruity between the 

 generic forms of the Mammalia which then existed in Europe 

 and any that actually exist on the great natural continent of 

 which Europe now forms part. It would seem, indeed, that 

 the further we penetrate into time for the recovery of ex- 

 tinct Mammalia, the further we must go into space to find 

 their existing analogues. To match the eocene Palseotheres 

 and Lophiodons we fetch Tapirs from Sumatra or South 

 America, and we must travel to the antipodes for Myrmeco- 

 bians, the nearest living analogues to the Amphitheres of our 

 oolitic strata. 



On the problem of the extinction of species little can be 

 said; and of the more mysterious subject of their coming into 

 being, nothing definite or demonstrative at present. As a 

 cause of extinction in times anterior to man, it is most reason- 

 able to assign the chief weight to those gradual changes in the 

 conditions affecting a due supply of sustenance to animals in 

 a state of nature which must have accompanied the slow alter- 



* Owen, Eeport on the Extinct Mammals of Australia, Trans. Brit. Associa- 

 tion, 1844. 



2 F 



