HYBRIDISM 



53 



from both parent-forms. Finally, then, although we are 

 as ignorant of the precise cause of the sterility of first 

 crosses and of hybrids as we are why animals and plants 

 removed from their natural conditions become sterile, yet 

 the facts given in this chapter do not seem to me 

 opposed to the belief that species aboriginally existed 

 as varieties. 



