PALEONTOLOGIGAL DISCOVERY. 235 



cies, and used all his great influence to. crush out the doctrine of evo- 

 lution, then first proj^osed. Cuvier's definition of a sjDecies, the domi- 

 nant one for half a century, was as follows : " A species compre- 

 hends all the individuals which descend from each other, or from a 

 common parentage, and those which resemble them as much as they 

 do each other." 



The law of " Correlation of Structures," as laid down by Cuvier, 

 has been more widely accepted than almost anything else that bears 

 his name ; and yet, although founded in truth, and useful within cer- 

 tain limits, it would certainly lead to serious error if applied widely 

 in the way he proposed. 



In his discourse he sums uj) this law as follows : "A claw, a shoul- 

 der-blade, a condyle, a leg or arm bone, or any other bone separately 

 considered, enables us to discover the description of teeth to which 

 they have belonged ; so also reciprocally we may determine the form 

 of the other bones from the teeth. Thus, commencing our investiga- 

 tion by a careful survey of any one bone by itself, a person who is 

 sufiiciently master of the laws of organic structure may, as it were, 

 reconstruct the whole animal to which that bone had belonged." 



We know to-day that unknown extinct animals can not be restored 

 from a single tooth or claw, unless they are very similar to forms 

 already known. Had Cuvier himself applied his methods to many 

 forms from the early Tertiary or older formations, he would have 

 failecl. If, for instance, he had had before him the disconnected frag- 

 ments of an Eocene Tillodont, he would undoubtedly have referred a 

 molar tooth to one of his pachyderms ; an incisor tooth to a rodent ; 

 and a claw-bone to a carnivore. The tooth of a Hesperornis would 

 have given him no possible hint of the rest of the skeleton, nor its 

 swimming feet the slightest clew to the ostrich-like sternum or skull. 

 And yet the earnest belief in his own methods led Cuvier to some of 

 his most important discoveries. 



Jean Lamarck (1744-1829), the philosopher and naturalist, a col- 

 league of Cuvier, was a learned botanist before he became a zoologist. 

 His researches on the invertebrate fossils of the Paris Basin, although 

 less striking, were not less important than those of Cuvier on the ver- 

 tebrates ; while the conclusions he derived from them form the basis 

 of modern biology. Lamarck's method of investigation was the same 

 essentially as that used by Cuvier, namely, a direct comparison of fos- 

 sils with living forms. In this way he soon ascertained that the fossil 

 shells imbedded in the strata beneath Paris were many of them ex- 

 tinct species, and those of different strata differed from each other. 

 His first memoir on this subject appeared in 1802,* and, with his later 

 works, effected a revolution in conchology. His " System of Inverte- 

 brate Animals " appeared the year before, and his famous " Philosophie 

 Zoologique " in 1809. In these two works, Lamarck first announced 

 * " Memoires sur les Fossiles des Environs dc Paris," 1802-'6. 



