312 STUDIES IN THE EVOLUTION OF ANIMALS 



way explains the ' remarkable phenomenon ' of 'rapid multiplication 

 of species in the early life of genera.' It is not impossible that in 

 those days what we would call species and genera may have been 

 more readily hybridisable, and by steady change of conditions and 

 consequent physiological differentiation, up to modern times, the 

 process of natural hybridisation may have become more difficult 

 and rare. 



Professor Huxley ^ says : ' In former periods of the world's 

 history there were animals which overstepped the bounds of 

 existing groups and tended to merge them into larger assemblages. 

 They show that animal organisation is more flexible than our 

 knowledge of recent forms might have led us to believe ; and 

 that many structural permutations and combinations of which the 

 present world gives us no indication may nevertheless have existed.' 



This seems very natural, for the further we go back in time the 

 less inheritance the species may have had at its back, and there- 

 fore the less time there may have been for the creation of a fixed- 

 habit of the nerve-centres in animals, which regulate everything. 

 Consequently they would be more variable. On the other hand, 

 the further we go forward in time, the more the habit of inheritance 

 would become confirmed, and therefore the ■a\ox& fixity of characters 

 would ensue. The oldness of the inheritance would then have 

 made it too strong to admit of much change, unless man interfered 

 with the natural process by artificial selection. 



Professor Huxley (p. 89) warns us not to be in a hurry to 

 conclude that because no organic remains are found in a deposit, 

 that therefore ' animals or plants did not exist at the time it was 

 formed,' for he has known fossil remains quite dissolved away, 

 leaving no trace but the casts which formerly surrounded them. 

 It might so happen that even the casts might be destroyed. 



' Lectures on Evolution — (Science and Hebrew Tradition), p. 102. 



