ix.] PALAEONTOLOGY AND EVOLUTION. 187 



have been glad enough to be able to find a good foun- 

 dation. So far, indeed, as the Invertebrata and the 

 lower Vertebrata are concerned, the facts and the con- 

 clusions which are to be drawn from them appear to me 

 to remain what they were. For anything that, as yetj 

 appears to the contrary, the earliest known Marsupials 

 may have been as highly organized as their living con- 

 geners ; the Permian lizards show no signs of inferiority 

 to those of the present day ; the Labyrinthodonts can - 

 not be placed below the living Salamander and Triton ; 

 the Devonian Ganoids are closely related to Polypterus 

 and to Lepidosiren. 



But when we turn to the higher Vertebrata, the results 

 of recent investigations, however we may sift and criticise 

 them, seem to me to leave a clear balance in favour of 

 the doctrine of the evolution of living forms one from 

 another. Nevertheless, in discussing this question, it is 

 very necessary to discriminate carefully between the dif- 

 ferent kinds of evidence from fossil remains which are 

 brought forward in favour of evolution. 



Every fossil which takes an intermediate place between 

 forms of life already known, may be said, so far as it is 

 intermediate, to be evidence in favour of evolution, inas- 

 much as it shows a possible road by which evolution 

 may have taken place. But the mere discovery of such 

 a form does not, in itself, prove that evolution took place 

 by and through it, nor does it constitute more than 

 presumptive evidence in favour of evolution in general. 

 Suppose A, B, C to be three forms, while B is inter- 

 mediate 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 modifi- 

 cations of B ; or A, B, and C may be independent modifi- 

 cations of some unknown D. Take the case of the Pigs, 



