THE EVOLUTION OF LIVING BEINGS. 15 



establish a species viz, to bring like to one and unlike to 

 different species. 



If we admit that identity of the different individuals, 

 to be included in one species, is the essential quality of 

 a species, and I doubt whether any naturalist will 

 object to this, the problem is quite simple: to establish 

 a species, one ought to bring together individuals of iden- 

 tical constitution. 



C'est simple comme bonjour; the trouble unfor- 

 tunately lies in the difficulty to determine identity 

 of constitution. 



As a matter of fact, one has long overlooked this 

 difficulty and thought that one could distinguish dif- 

 ferent constitutions at sight, even without taking very 

 much pain. 



This led the older botanists to the acceptance of 

 groups of supposedly identical individuals as species 

 which later generations have shown to consist of a 

 mixture of individuals of sometimes very different 

 constitutions. 



One usually expresses this shortly, by saying that 

 the older botanists considered genera to be species. 



It is useless to go into the details of these mistakes 

 and their causes ; the obvious primary cause is a lack 

 of discriminating power which prevented them from 

 seeing the differences between the individuals, they 

 thought to be indentical. 



Such a lack of discriminating power can however 

 not be reproached to Linnaeus, so that, if identity of 

 constitution can be established at sight, there is every 

 reason to believe, a priori, that the Linnean species will 



