324 GEOLOGICAL BIOLOGY. 



of Science, on " The Rise of the Mammalia in North 

 America,"* in which a minute study is made of the law of 

 evolution as expressed in the teeth of mammals, says: " The 

 evolution of a family like the Titanotheres presents an unin- 

 terrupted march in one direction. While apparently prosper- 

 ous and attaining a great size, it was really passing into a 

 great corral of inadaptation to the grasses which were in- 

 troduced in the Middle Miocene. So with other families and 

 lesser lines, extinction came in at the end of a term of devel- 

 opment and high specialization. ... A certain trend of de- 

 velopment is taken leading to an adaptive or inadaptive final 

 issue ; but extinction or survival of the fittest seems to exert 

 little influence en route. The changes en route lead us to be- 

 lieve either in predestination a kind of internal perfecting 

 tendency, or in kinetogenesis. For the trend of evolution is 

 not the happy resultant of many trials, but is heralded in 

 structures of the same form all the world over and in age 

 after age, by similar minute changes advancing irresistibly 

 from inutility to utility. It is an absolutely definite and 

 lawful progression. The infinite number of contemporary 

 developing, degenerating, and stationary characters preclude 

 the possibility of fortuity. There is some law introducing 

 and regulating each of these variations, as in the variations 

 of individual growth." f 



* Am. Jour. Sci., vol. XLVI. pp. 379-392 and 448-466. f pp. 465, 466. 



