160 THE DOCTRINE OF DESCENT. 
selection in the strict Darwinian sense is inapplicable. 
Two species of butterflies, differing only in a few specks 
or pencilings, or the notches on the wings, are in 
our estimation of perfectly 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 morphological 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 morphological characters may be estab- 
lished by the effects of isolation only.” The inapplica- 
bility of natural selection to the evolution of purely 
morphological variations was first pointed out by 
Nageli.” With reference to this subject, 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 animals, more espe- 
cially 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 confine 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 bene- 
ficial 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- 
