XI 



PALEONTOLOGY 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 Ancplotheridcc, and the Ruminants. 

 The AnoplotJieridce 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 Anajylotheridce, 

 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 tjipe ; and if, farther, it 

 can be proved that they occur m 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, 



