48 Darwin, and after Darwin, 
it is necessary that it should, if both sets of organs are 
to be adapted to perform the same functions. Now 
this, again, is just what one would expect to find as 
the universal rule on the theory of descent, with modi- 
fication of ancestral characters. But, on the opposite 
theory of special creation, I know not how it is to be 
explained that among so many instances of close 
superficial resemblance between creatures belonging 
to different branches of the tree of life, there are 
no instances of any real or anatomical resemblance. 
So far as their structures are adapted to perform a 
common function, there is in all such cases what may 
be termed a deceptive appearance of some unity of 
ideal; but, when carefully examined, it is always 
found that two apparently identical structures occurring 
on different branches of the classificatory tree are in 
fact fundamentally different in respect of their struc- 
tural plan. 
Lastly, we have seen that one of the guiding prin- 
ciples of classification has been empirically found to 
consist in setting a high value on “ chains of affinities.” 
That is to say, naturalists not unfrequently meet 
with a long series of progressive modifications of type, 
which, although it cannot be said that the continuity 
is anywhere broken, at last leads to so much divergence 
of character that, but for the intermediate links, the 
members at each end of the chain could not be sus- 
pected of being in any way related. Well, such cases 
of chains of affinity obviously tell most strongly in 
favour of descent with continuous modification ; while 
it is impossible to suggest why, if all the links were 
separately forged by as many acts of special creation, 
there should have been this gradual transmutation of 
