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 o{ 



