286 Darwin, and after Darwin. 
of water-weed which -had been introduced from 
America, that considerable expense had to be incurred 
in order to clear the river for traffic. In New Zealand 
the same thing has happened with the European 
water-cress, and in Australia with the common rabbit. 
So it is doubtless true, as one of the natives is said to 
have philosophically remarked, “ the white man’s rat 
has driven away our rat, the European fly drives away 
our fly, his clover kills our grass, and so will the Maoris 
disappear before the white man himself.” Innumer- 
able other cases to the same effect might be quoted ; 
and they all go to establish the fact that forms less 
fitted to survive succumb in their competition with 
forms better fitted. 
Secondly, there is a general consideration of the 
largest possible significance in the present connexion— 
namely, that among all the millions of structures and 
instincts which are so invariably, and for the most part 
so wonderfully, adapted to the needs of the species 
presenting them, we cannot find a single instance, 
either in the vegetable or animal kingdom, of a 
structure or an instinct which is developed for the 
exclusive benefit of another species. Now this great 
and general fact is to my mind a fact of the most 
enormous, not to say overwhelming, significance. The 
theory of natural selection has now been before the 
world for more than thirty years, and during that time 
it had stood a fire of criticism such as was never en- 
countered by any scientific theory before. From the 
first Darwin invited this criticism to adduce any single 
instance, cither in the vegetable or animal kingdom, of 
a structure or an instinct which should unquestionably 
