APPENDIX C. 



SOME EXTRACTS FROM THE AUTHOr's NOTE-BOOKS. 



Bearing of Weismannism on Physiological Selection. — If 

 in view of other considerations I could fully accept Professor 

 Weismann's theory of heredity, it would appear to me in no 

 small measure to strengthen my own theory of physiological 

 selection. For Weismann's theory supposes that all changes 

 of specific type must have their origin in variations of a 

 continuous germ-plasm. But the more the origin of species is 

 referred directly to variations arising in the sexual elements, 

 the greater is the play given to the principles of physiological 

 selection ; while, on the other hand, the less standing-ground 

 is furnished to the theory that cross-infertility between allied 

 species is due to " external conditions of life," " prolonged 

 exposure to uniform change of conditions," "structural 

 modifications re-acting on the sexual functions " ; or, in 

 short, that " somatogenetic " changes of any kind can of 

 themselves induce the " blastogenetic " change of cross- 

 infertility between progeny of the same parental stock. 



Cross-infertility and Diversity of Life. — Observe that one 

 great consequence of duly recognizing the importance of inter- 

 crossing is indefinitely to raise our estimate of the part played 

 by the principle of cross-infertility in diversifying organic 

 nature. For whenever in any line of descent the bar of 



^Doctrine of Descent and Darwinism, Eng. trans, p. 139. 



