234 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



certain that the geological ages witnessed the 

 extinction of a very great number of phyletic 

 branches I might almost say of the majority, 

 for, among these innumerable branches, relatively 

 very few have possessed the vital force suffi- 

 cient to continue them down to our own times. 

 But if the mere fact of these extinctions is easily 

 proved, on the other hand, the precise cause of it 

 has long remained obscure, and even at the present 

 day is far from being fully apparent. It is not 

 that there has been any lack of hypotheses since 

 the old conception of Cuvier as to the destruction 

 of fossil species by revolutions of the globe and the 

 ingenious explanation of Darwin founded on the 

 struggle for life. The direct strife with other 

 species not seeming applicable to the great mam- 

 mals and the gigantic Dinosaurians, the illustrious 

 reviver of transformism was thrown back as 

 regards these giant beings on the difficulty of 

 procuring a sufficient supply of food an explana- 

 tion of almost infantine weakness, seeing that 

 it refers to herbivorous animals who dwelt in 

 almost boundless continents, such as the vast 

 Jurassic plains of Central and Western America 

 must have been.* Darwin also rightly recognized 

 the point of the objections raised against the 

 hypothesis of the struggle for life from the well- 

 known fact of the almost simultaneous extinc- 

 tion of all the branches of certain great groups 

 spread over vast geographical districts, such as the 



* The Dinosaurs were not all herbivorous. But apart from this, 

 the extinction of the American Bison in our own days may show 

 how enormous is the range of pasture that wild animals of this order 

 require. ED. 



