14 Darwin, and after Darwin. 



apogamy alone to produce any change of type in an 

 isolated portion of the species, while a highly variable 

 species (such as the Ruff) would rapidly change in 

 any portion that might be indiscriminately isolated. 

 It was in order to recognize this additional and very 

 important factor that I chose the name Independent 

 Variability whereby to designate the diversifying 

 influence of merely indiscriminate isolation, or apo- 

 gamy. Later on Mr. Gulick published his elaborate 

 papers upon the divergence of type under all kinds of 

 isolation ; and retained my term Independent, but 

 changed Variability into Generation. I point this 

 out merely for the sake of remarking that his In- 

 dependent Generation is exactly the same principle 

 as my Independent Variability, and Delbceuf 's Mathe- 

 matical Law. 



Now, while I fully agree with Mons. Giard where 

 he says, in the introductory lecture of his course on 

 The Factors of Evolution \ that sufficient attention 

 has not been hitherto given by naturalists to this 

 important factor of organic evolution (apogamy), 

 I think I have shown that among those naturalists 

 who have considered it there is a sufficient amount of 

 agreement. Per contra, I have to note the opinion 

 of Mr. Wallace, who steadily maintains the impossi- 

 bility of any cause other than natural selection (i. e. 

 one of the forms of homogamy) having been concerned 

 in the evolution of species. But at present it is enough 

 to remark that even Professor Ray Lankester whose 

 leanings of late years have been to the side of ultra- 

 Darwinism, and who is therefore disposed to agree 



1 Revue Scientifique, Nov. 33, 1889. 



