CONFORMITY TO ENVIRONMENT 195 



vertebrate could not go. There his mail-clad competi- 

 tors were too strong for him. Those which settled and 

 tried to compete in this sort of life perished. We may 

 have to except the ascidia, but they paid for their suc- 

 cess by the loss of nearly all their vertebrate character- 

 istics. The future progress of vertebrates depended 

 upon their continual activity in the swimming life. 

 And they were forced by their environment to main- 

 tain this. Otherwise they might, probably would, 

 never have attained their present height of organiza- 

 tion. Certainly at this time you would have found it 

 hard to believe that the victory was to fall to these 

 weaker and smaller vertebrates. 



Let us come down to a later period. Keptiles, 

 mammals, and birds are struggling for supremacy. Of 

 the power and diversity of form of these old reptiles 

 we have generally no adequate conception. The 

 forms now living are but feeble remnants. There 

 were huge sea-serpents, and forms like our present 

 crocodiles, but far more powerful. Others apparently 

 resembled in form and habit the herbivorous and 

 carnivorous mammals of to-day. Others strode or 

 leaped on two legs. And still others flew like bats 

 or birds. They were terrible forms, with coats of 

 mail and powerful jaws and teeth. And they were 

 active and swift. When we look at them we see that 

 the vertebrate, though slow in gaming the lead, is 

 sure to hold it. The internal skeleton gave fewer 

 advantages at the start ; its greatest superiority had 

 lain in future possibilities. 



But which vertebrate is heir to the future ? It 

 would have been a hard choice between reptile and 

 bird. I feel sure that I, for one, should not have se- 



