PREFACE xv 



the common form, acquires in the course of ages a 

 numerical ascendancy over what,' was the common 

 form until the latter is finally exterminated, and 

 individuals possessed of the superior variation become 

 themselves the common form. Thus one form super- 

 sedes another. 



But in the ages during which one form has been 

 superseded by another the evolutionary gain has only 

 been an infinitesimal accretion of something that is 

 beneficial to the organism alone which, possessing it 

 from the beginning, had the intelligence to select it. 



A long succession of similar infinitesimal accretions 

 follows, all of secular duration. After hundreds, 

 perhaps many hundreds, of such secular periods, each 

 adding its infinitesimal accretion, the result is a form 

 sufficiently distinct and differentiated from that which 

 we have seen starting on the path of development to 

 entitle it to be considered a new species. 



Now, how vast must have been the number, I will 

 not say of new forms each with its infinitesimal accre- 

 tion, but of new specific forms, each the resultant of 

 the hundreds of infinitesimal accumulations that were 

 required to give it its differentiation from the species 

 from which it was evolved, that followed each other 

 in succession while the fish was being developed into 

 the mammal ? How vast, I ask, must have been the 

 number of distinct specific forms that marked this 

 period of evolution ? 



Some geologists have averred that a period of one 

 hundred million years, which they are of opinion 

 b 



