IN MODERN SCIENCE. 121 



proves this more clearly than that which re- 

 lates to the degradation of old forms. When, 

 for example, the reptiles of the Mesozoic Age 

 were the lords of creation, there was appar- 

 ently no place for the larger Mammalia which 

 appear at the close of the reptile dynasty. So 

 in the Palaeozoic, when trees of the cryp- 

 togamous type predominated, there seems to 

 have been no room in nature for the forests 

 of modern type which succeeded them. Thus 

 the earth at every period was fully peopled 

 with living beings — at first with low and gen- 

 eralized structures which attained their maxima 

 at early stages and then declined, and after- 

 ward with higher forms which took the places 

 of those that were passing away. These latter, 

 again, though their dominion was taken from 

 them, were continued in lower positions under 

 the new dynasties. Thus none of the lower 

 types of life introduced was finally abandoned, 

 but, after culminating in the highest forms of 

 which it was capable, each was still continued, 

 though with fewer species and a lower place. 

 Examples of this abound in the history of all 

 the leading groups of animals and plants. 



4. There is thus a continued plan and order 

 in the history of Hfe which cannot be fortuitous. 

 11 



