CHAPTER II. 



Isolation {contintud). 



I WILL now recapitulate the main doctrines which 

 have been set forth in the foregoing chapter, and then 

 proceed to consider the objections which have been 

 advanced against them. 



It must be remembered that by isolation I mean 

 exactly what Mr. Gulick does by " Segregation," 

 and approximately what Professpr Weismann does 

 by " Amixia " — i. e. the prevention of intercrossing. 



Isolation occurs in very many forms besides the 

 geographical, as will be more fully shown at the end 

 of this chapter ; and in all its forms it admits of 

 degrees. 



It also occurs in two very different species or 

 kinds — namely, discriminate and indiscriminate. These 

 I have called respectively Homogamy and Apogamy. 

 This all-important distinction has been clearly recog- 

 nized by Mr. Gulick, as a result of his own thought 

 and observation, independently of anything that I have 

 published upon the subject. 



In view of this distinction Isolation takes rank with 

 Heredity and Variability as one of the most funda- 

 mental principles of organic evolution. For, if these 



