234 Darwin, and after Darwin. 



definitions of a species that are logically possible 1 . 

 Which of them is chosen by those who maintain 

 the necessary usefulness of all specific characters? 

 Observe, it is for those who maintain this doctrine 

 to choose their definition : it is not for me to do so. 

 My contention is, that the term does not admit of 

 any definition sufficiently close and constant to serve 

 as a basis for the doctrine in question and this for 

 the simple reason that species-makers have never 

 agreed among themselves upon any criterion of specific 

 distinction. My opponents, on the other hand, are 

 clearly bound to take an opposite view, because, 

 unless they suppose that there is some such definition 

 of a species, they would be self-convicted of the 

 absurdity of maintaining a great generalization on 

 a confessedly untenable basis. For example, a few 

 years ago I was allowed to raise a debate in the 

 Biological Section of the British Association on the 

 question to which the present chapters are devoted. 

 But the debate ended as I had anticipated that it 

 must end. No one of the naturalists present could 

 give even the vaguest definition of what was meant by 



1 It is almost needless to say that by a definition as " logical " 

 is meant one which, while including all the differentiae of the thing 

 denned, excludes any qualities which that thing may share in common 

 with any other thing. But by definitions as " logically possible " I mean 

 the number of separate definitions which admit of being correctly given 

 of the snme thing from different points of view. Thus, for instance, in 

 the present case, since the above has been in type the late M. Quatre- 

 fages' posthumous work on Darwin et ses Precurseurs Francois has 

 been published, and gives a long list of definitions of the term *' species " 

 which from time to time have been enunciated by as many naturalists 

 of the highest standing as such (pp. 186-187). But while none of 

 these twenty or more definitions is logical in the sense just defined, 

 they all present one or other of the differentiae given by those in 

 the text 



