14 THE EVOLUTION OF LIVING BEINGS. 



phe est pour un naturaliste I'dpreuve la plus redoutable 

 de toutes. II suit que chaque mot sera pesd, que toute 

 idee nouvelle pourra itre taxde d'hirisie et que des 

 notions fausses sur cette base des sciences naturelles, 

 jettent ses iravaux de description dans un discrddit 

 mdritd. 



And Darwin says in his Origin of Species p. 30: 



Nor shall I here discuss the various definitions which 

 have been given of the term species. No one definition has 

 satisfied all naturalists; yet every naturalist knows vague- 

 ely what he means when he speaks of a species. 



Unfortunately, it is just the vagueness of this kind of 

 knowledge which has caused endless trouble and there 

 is a good deal of truth in the ..badinage" of Moritzi 

 (Reflexions sur I'espece. Soleure (Solothum) 1842) who 

 tells of a professor of philosophy of his acquaintance, 

 qui avait admis I'espice, comme nous tous, d priori, sans 

 savoir en quoi elle consiste. C'est seulement plus tard, 

 he continues, que I'idde lui est venue de se rendre compte 

 de ce sentiment obscur qui I'a guidd depuis son enfance. 



All this fits our case; all theories of evolution have, 

 until quite recently, been guided by a vague knowledge 

 of what a species is, and consequently have inevitably 

 been vague themselves. 



The remedy is obvious: one has, before one proposes 

 any theory of evolution, to define the terms which 

 one is going to use. 



This is not so difficult as may appear at first sight, 

 because we can be guided by the aim»which obviously 

 every systematist, no matter of which period or of 

 which nationality, had before him when he tried to 



