II PALAEONTOLOGY AND EVOLUTION 349 



sumptive evidence in favour of evolution in 

 general. Suppose A, B, C to be three forms, 

 while B is intermediate in structure between A 

 and C. Then the doctrine of evolution offers four 

 possible alternatives. A may have become C by 

 way of B ; or C may have become A by way of B ; 

 or A and C may be independent modifications of 

 B ; or A, B, and C may be independent modifica- 

 tions of some unknown D. Take the case of the 

 Pigs, the Anoplotheridce, and the Ruminants. 

 The Anoplotheridce are intermediate between the 

 first and the last ; but this does not tell us whether 

 the Ruminants have come from the Pigs, or the 

 Pigs from Ruminants, or both from Anoplotheridce, 

 or whether Pigs, Ruminants, and Anoplotheridce 

 alike may not have diverged from some common 

 stock. 



But if it can be shown that A, B, and C exhibit 

 successive stages in the degree of modification, or 

 specialisation, of the same type ; and if, further, it 

 can be proved that they occur in successively 

 newer deposits, A being in the oldest and C in 

 the newest, then the intermediate character of B 

 has quite another importance, and I should accept 

 it, without hesitation, as a link in the genealogy 

 of C. I should consider the burden of proof to be 

 thrown upon any one who denied C to have been 

 derived from A by way of B, or in some closely 

 analogous fashion ; for it is always probable that 

 one may not hit upon the exact line of filiation, 



