Variation, Geographical Distribution, and Succession. 95 



stood, all three are equally independent of physical cause and 

 effect, are equally supernatural. 



In comparing preceding periods with the present and with 

 each other, most naturalists and palaeontologists now appear to 

 recognize a certain number of species as having survived from 

 one epoch to the next, or even through more than one formation, 

 especially from the Tertiary into the Posttertiary period, and 

 from that to the present age. M. Agassiz is understood to be- 

 lieve in total extinctions and total new creations at each succes- 

 sive epoch, and even to recognize no existing species as ever co- 

 temporary with extinct ones, except in the case of recent exter- 

 minations. 



These peculiar views, if sustained, will effectually dispose of 

 every form of derivative hypothesis. 



Returning for a moment to DeCandolle's article, we are dis- 

 posed to notice his criticism of Linnseus's " definition " of the 

 term species (Phil. Bot. No. 157), " Species tot numeramus quot 

 diver see formse in principle sunt creatse," which he declares illo- 

 gical, inapplicable, and the worst that has been propounded. 

 " So, to determine if a form is specific, it is necessary to go back 

 to its origin, which is impossible. A definition by a character 

 which can never be verified is no definition at all." 



Now, as Linnaeus practically applied the idea of species with 

 a sagacity which has never been surpassed and rarely equalled, 

 and, indeed, may be said to have fixed its received meaning in 

 natural history, it may well be inferred that in the phrase above 

 cited he did not so much undertake to frame a logical definition 

 as to set forth the idea which, in his opinion, lay at the founda- 

 tion of species, on which basis A. L. Jussieu did construct a 

 logical definition : " nunc rectius definitur perennis individuorum 

 similium successio continuata generatione renascentium." The 

 fundamental idea of species, we would still maintain, is that of 

 a chain, of which genetically connected individuals are the links. 

 That, in the practical recognition of species, the essential cha- 

 racteristic has to be inferred, is no great objection, the general 

 fact that like engenders like being an induction from a vast 

 number of instances, and the only assumption being that of the 

 uniformity of nature. The idea of gravitation, that of the ato- 

 mic constitution of matter, and the like, equally have to be veri- 

 fied inferentially. If we still hold to the idea of Linnaeus^ and 

 of Agassiz, that existing species were created independently and 

 essentially all at once at the beginning of the present era, we 

 could not improve the propositions of Linnaeus and of Jussieu. 

 If, on the other hand, the time has come in which we may accept, 

 with DeCandolle, their successive origination, at the commence- 

 ment of the present era or before, and even by derivation from 



