l6o THE DOCTRINE OF DESCENT. 



Darwinian sense is inapplicable. Two species of but- 

 terflies, differing only in a few specks or pencilings, or 

 the notches on the wings, are in our estimation of per- 

 fectly equal physiological value; they are morphological 

 species. Weismann sets up the proposition that " the 

 colouring and penciling of the upper surface of the 

 wing in butterflies are to be regarded as purely morpho- 

 logical characters, excepting in cases of mimicry and 

 protective uniform colouring." He shows also by other 

 examples that, " under certain circumstances and within 

 a comparatively small range, new as well as morpho- 

 logical characters may be established by the effects of 

 isolation only." The inapplicability of natural selection 

 to the evolution of purely morphological variations was 

 first pointed out by Nageli.*" With reference to this sub- 

 ject, Darwin with magnanimous modesty observes: " I 

 now admit, .after reading the essay by Nageli on plants, 

 and the remarks by various authors with respect to ani- 

 mals, more especially those recently made by Professor 

 Broca,^° that, in the earlier editions of my ' Origin of 

 Species,' I probably attributed too much to the action 

 of natural selection or the survival of the fittest. I have 

 altered the fifth edition of the ' Origin ' so as to con- 

 fine my remarks to adaptive changes of structure. I 

 had not formerly sufficiently considered the existence of 

 many structures, which appear to be, as far as we can 

 judge, neither beneficial nor injurious, and this I believe 

 to be one of the greatest oversights as yet detected in my 

 work." " 



We are disposed to think that the oversight with 

 which Darwin charges himself is not so great, as it is 

 here a question of the more indifferent species, not affect- 



