l8o Darwin and Roiuaiies dealt luith. 



open to Dr. Brooks to say that this is an exceptional 

 case wholly ; but we did not understand his expression 

 above to apply to whole species as exceptions, but 

 only to individuals or groups of individuals within the 

 species ; and certainly as to cuckoos Dr. Brooks has 

 himself in more than one point suggested this as 

 regards the species ; yet, certainly in this case, the 

 species as regards females show more of real and 

 inward modification than the males. Can this possibly 

 be a reason why the females decrease at such a rate 

 or the males increase so rapidly ; and how does it 

 stand in relation to Dr. Brooks' generalization given 

 above ? 



XXV. 



Mr. Romanes writes : " From the first Darwin 

 invited criticism to adduce a single instance, either 

 in the vegetable or animal kingdom, of a structure or 

 an instinct which should unquestionably be proved to 

 be of exclusive use (or benefit) to any species other 

 than the one presenting it. He even went so far as to 

 say that if any one instance conld be shown he wonld 



surrender his whole theory on the strength of it 



" Now, as this invitation has been before the world 

 for so many years, and has not yet been answered by 

 any naturalist, we may by this time be pretty confi- 

 dent that it never will be answered. How tremendous, 

 then, is the significance of this fact in its testimony to 

 Darwin's theory. . . . Therefore, I say, that this 

 immensely large and general fact speaks with literally 

 immeasureable force in favour of natural selection, as 



