DIVERGENCE 299 



sification progressed in the sea and later on the land 

 until the world of to-day arrived. 



The vastness of time necessary for the evolutionary 

 phenomena was at first supposed to be one of the strong- 

 est arguments against it, for the astronomers and geolo- 

 gists found it impossible to admit the age of the world's 

 crust to be sufficient to permit them. But this objection 

 has been effaced, for the discovery of radium by which 

 the sun makes good its heat loss and the further dis- 

 covery that the earth possesses self-sustaining heat 

 centres and is not entirely dependent upon the sun for 

 its supply, have upset all past calculations in cosmogonies 

 and now permit the biologists almost infinite time for 

 evolution. 



But granting the process of evolution in progress, by 

 what means does it continue? By a succession of fits 

 and starts, leaps and bounds, or by a series of continuous 

 and almost imperceptible changes, or does it do so by 

 means of both? Present opinion is in favor of the former; 

 past opinion of the latter; both may be correct. 



REFERENCES. 



CHARLES DARWIN: "The Origin of Species by Means of Natural 

 Selection." "The Descent of Man." "The Variation 

 of Animals and Plants under Domestication." 



HERBERT SPENCER: "First Principles." "Principles of Biology." 



E. D. COPE: "The Origin of the Fittest," N. Y., 1887. "The 



Primary Factors in Organic Evolution," Chicago, 1896. 



"The Origin of Genera," 1868. 

 GEORGE JOHN ROMANES: " Darwin And After Darwin," Chicago, 



1896. 

 ERNST HAECKEL: "The Riddle of the Universe," Translated by 



Joseph McCabe, N. Y., 1900. " The History of Creation." 

 THOMAS H. HUXLEY: "Man's Place in Nature," and other 



Essays. 



ROBERT CHAMBERS: "Vestiges of the Natural History of Crea- 

 tion," London, 1887. 



HUGO DE VRIES: "Species and Varieties, their Origin by 

 Mutation," Chicago, 1906. 



VERNON S. KELLOGG: "Darwinism To-day," N. Y., 1908. 



F. W. HUTTON: " Darwinism and Lamarckism." N. Y., 1899. 



