308 EVOLUTION IN BIOLOGY. [LECT. 



created, as such, within the limits in which we find 

 them. And as the hypothesis of " specific centres," 

 thus formulated, was heterodox from the theological 

 point of view, and unintelligible under its scientific 

 aspect, it may be passed over without further notice, 

 as a phase of transition from the creational to the 

 evolutional hypothesis. 



8. In fact, the strongest and most conclusive 

 arguments in favour of evolution are those which 

 are based upon the facts of geographical, taken in 

 conjunction with those of geological, distribution. 



Both Mr. Darwin and Mr. Wallace lay great stress 

 on the close relation which obtains between the exist- 

 ing fauna of any region and that of the immediately 

 antecedent geological epoch in the same region ; and 

 rightly, for it is in truth inconceivable that there 

 should be no genetic connection between the two. It 

 is possible to put into words the proposition that all 

 the animals and plants of each geological epoch were 

 annihilated, and that a new set of very similar forms 

 was created for the next epoch ; but it may be doubted 

 if any one who ever tried to form a distinct mental 

 image of this process of spontaneous generation on the 

 grandest scale, ever really succeeded in realising it. 



Within the last twenty years, the attention of the 

 best palaeontologists has been withdrawn from the 

 hodman's work of making "new species" of fossils, 

 to the scientific task of completing our knowledge of 

 individual species, and tracing out the succession of 

 the forms presented by any given type in time. 



Those who desire to inform themselves of the 



