16 THE WANDERINGS OF ANIMALS [OH. 



came to the front the importance of the geological 

 record, hand in hand with the fossil data and the 

 search for the natural affinities, the pedigrees of the 

 organisms. The biologists not only set the problems ; 

 they alone can check the solutions offered by physicists 

 and geologists, and rightly so, because they concern 

 living matter, and life has been continuous ever since 

 the unfathomable dawn. The mere fact that sub- 

 tropical plants occur in the Miocene of Spitzbergen, 

 led to an hypothetical shifting of the axis of the world 

 rather than to the assumption, by way of explanation, 

 that the plants themselves might have changed their 

 nature. As the men of the Dordogne in the south 

 of France hunted the reindeer, we want explanations 

 why it was so cold. And since there are plenty of 

 bones of hippopotamus in the Cambridge gravel, 

 washed into it out of Pliocene crag, we require an 

 answer as to why East Anglia enjoyed a mean annual 

 temperature perhaps 20 degrees higher than now. 



One of the most valuable aids, often the only 

 means for reconstructing the face of the earth in 

 by-gone periods, is afforded by fossils, but only the 

 morphologist can pronounce as to their trustworthi- 

 ness as witnesses, because of the danger of mistaking 

 analogous for homologous forms. This difficulty ap- 

 plies equally to living groups and is of the utmost 

 importance. 



The affinity question can be settled only by 



