INTRODUCTION. 139 



of four-footed animals on the globe, and at the present day 

 there is little chance of new living species being discovered. 

 Certainly the incompleteness and often poor preservation of 

 the fossil remains of land mammals offered obstacles to exact 

 identification. But they could be surmounted with the help 

 of the laws of correlation enunicated by him, according to 

 which all the individual parts of an organism stand in a 

 definite morphological relationship to one another, so that one 

 part could not undergo a change without a corresponding 

 modification taking place in the correlated parts. 



Summarising the results of his own researches on fossil 

 bones, Cuvier shows that these occur in strata of different age, ' 

 that the fishes, amphibians, and reptiles existed before 

 mammalia, that the extinct genera(/W^<?//#mz/#z, Anoplotherium, 

 etc.) occur in older strata than the forms belonging to living 

 genera, and that the few fossil forms which differ little from 

 living species are restricted to the very youngest deposits in 

 river alluvium, marshes, caves, etc. 



The exact investigation of fossil mammalia gives, according to 

 Cuvier, no ground for the Lamarckian conception that the forms 

 still existing have been produced by gradual modifications of 

 the forms that had previously existed. On the contrary, 

 Cuvier's conception was that specific features are constant^ and \ 

 remain so even in domesticated breeds. 



Regarding the length of period during which man has ex- 

 isted on the globe, Cuvier points out that no human remains 

 have been found along with the latest accumulations of four- 

 footed animals in Europe, Asia, and America, and that in all 

 probability man did not make his appearance in those parts of 

 the globe until after the last great world catastrophe. And 

 although no exact determination of the time is attainable, 

 Cuvier calculates from data of the rate of increase in sand- 

 dunes, in the thickness of peat deposits, and river deltas, that 

 the last great earth's revolution took place not more than 

 5000 or 6000 years ago. Large parts of the terrestrial sur- 

 faces of the globe were then submerged, and the floor of 

 the former ocean was in many places upraised and re-con- 

 stituted as islands and continents. Some few human beings 

 who were not destroyed during this catastrophe wandered into 

 the new lands and multiplied, founded colonies, erected monu- 

 ments, collected facts of natural history, conceived scientific 

 systems. 



