140 ORGANIC EVOLUTION CONSIDERED 



through all geological time wide gulfs between groups 

 of organic beings which are not bridged by inter- 

 mediate forms. And very remarkable it is that the 

 gulfs between the great groups of animals are, in 

 most cases, quite as wide in the beginning as they are 

 in the end. It is a quite universal rule that species, 

 orders, and classes appear suddenly, as if by substitu- 

 tion, and not by evolution. 



