148 REVIEWS. 



tions at each successive epoch, and even to recognize no exist- 

 ing species as ever contemporary with extinct ones, except in 

 the case of recent exterminations. 



These peculiar views, if sustained, will effectually dispose of 

 every form of derivative hypothesis. 



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

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

 term species (" Philosophia Botanica," No. 157) : " Species 

 tot numeramus quot diversae forniae in principio sunt creatae," 

 — which he declares illogical, 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." 



2s ow, 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 foundation of species. On which basis A. L. Jussieu 

 did construct a logical definition : " nunc rectius definitur pe- 

 rennis individuorum similium successio continuata generatione 

 renascentium." The fundamental idea of species, we would 

 still maintain, is that of a chain, of which genetically-con- 

 nected individuals are the links. That, in the practical rec- 

 ognition of species, the essential characteristic has to be in- 

 ferred, is no great objection, — the general fact that like 

 engenders like being an induction from a vast number of in- 

 stances, and the only assumption being that of the uniformity 

 of nature. The idea of gravitation, that of the atomic consti- 

 tution of matter, and the like, equally have to be verified in- 

 ferentially. 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 better the propositions of Linnaeus and of Jussieu. 

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

 with De Candolle, their successive origination, at the com- 



