170 Darwin, and after Darwin, 



although coinciding with the Wallacean up to the 

 point of maintaining utility as the only principle 

 which can be concerned in the origin of species, 

 designedly excludes the Wallacean doctrine where 

 this proceeds to extend any similar deduction to the 

 case of specific characters l . 



In the next place, and with special reference to the 

 Wallacean doctrine, it is of importance to observe 

 that, up to a certain point there is complete agreement 

 between Darwinists of all schools. We all accept 

 natural selection as a true cause of the origin of species 

 (though we may not all subscribe to the Huxleyan 

 deduction that it is necessarily a cause of the origin of 

 all species). Moreover, we agree that specific characters 

 are often what is called rudimentary or vestigial ; and, 

 once more, that our inability to detect the use of 

 any given structure or instinct is no proof that such 

 a structure or instinct is actually useless, seeing that 

 it may very probably possess some function hitherto 

 undetected, or possibly undetectable. Lastly, we all 

 agree that a structure which is of use may incidentally 

 entail the existence of some other structure which is 

 not of use ; for, in virtue of the so-called principle of 

 correlation, the useless structure may be an indirect 

 consequence of natural selection, since its development 

 may be due to that of the useful structure, with the 

 growth of which the useless one is correlated. 



Nevertheless, while fully conceding all these facts 

 and principles to the Wallacean party, those who 

 think with Professor Huxley and still more, of course, 

 those few naturalists who think as I do are unable 



1 Professor Huxley's views upon this matter are quoted in extenso in 

 Appendix II. 



