Characters as Adaptive and Specific. 235 



a species — or, consequently, of a character as specific. 

 On this account the debate ended in as complete 

 a destruction as was possible of the doctrine that 

 all the distinctive characters of every species must 

 necessarily be useful, vestigial, or correlated. For it 

 became unquestionable that the same generalization 

 admitted of being made, with the same degree of 

 effect, touching all the distinctive characters of every 

 " snark." 



Probably, however, it will be thought unfair to have 

 thus sprung a difficult question of definition in oral 

 debate. Therefore I allude to this fiasco at the 

 British Association, merely for the purpose of em- 

 phasizing the necessity of agreeing upon some defini- 

 tion of a species, before we can conclude anything with 

 regard to the generalization of specific characters as 

 necessarily due to natural selection. But when a 

 naturalist has had full time to consider this funda- 

 mental matter of definition, and to decide on what 

 his own shall be, he cannot complain of unfairness on 

 the part of any one else who holds him to what he 

 thus says he means by a species. Now Mr. Wallace, 

 in his last work, has given a matured statement of 

 what it is that he means by a species. This, there- 

 fore, I will take as the avowed basis of his doctrine 

 touching the necessary origin and maintenance of all 

 specific characters by natural selection. His definition 

 is as follows : — 



" An assembla<Te of individuals which have become somewhat 



o 



modified in structure, form, and constitution, so as to adapt them 

 to slightly different conditions of life ; which can be differen- 

 tiated from alhed assemblages ; which reproduce their like ; which 

 usually breed together ; and, perhaps, when crossed with their 



