122 THE METHOD OF DARWIN. 



reached. When, at the beginning of this cen- 

 tury, it was finally approached, and the natural 

 affinities of plants and animals were brought 

 out by it, the doctrine of descent was inevitable; 

 and it came. When Darwin had once become 

 impressed with its truth, and had found the 

 cause of modification, it was first of all neces- 

 sary to show that the great bodies of known 

 facts harmonized with his doctrines. The facts 

 of distribution, palaeontology, embryology, rudi- 

 mentary organs, etc., were all reduced. Each set 

 of facts presented its own difficulties. 



Up to the present century it was regarded as 

 an axiom in taxonomy that the structures of 

 most importance to the animals possessing 

 them must be of most importance for the pur- 

 poses of classification. It is worth while to 

 note that this was accepted as self-evident, as 

 being beyond the necessity of proof. Systema- 

 tists were approaching the "natural arrange- 

 ment," and De Candolle discovered empirically 

 the rule that there is usually an inverse ra- 

 tio between the taxonomic and the functional 

 value of a structure ; but he could suggest no 

 reason for the paradox. Darwin's theory fur- 

 nished the philosophical explanation. 1 The 



1 Origin of Species, pp. 362-373. Romanes, Darwin and 

 After Darwin, pp. 34-37- 



