246 EEV. J. T. GULICK ON" DIYEEGENT EVOLrTION 



in connection with different forms of partial Segregation will 

 now be considered. 



17, 18. Segregate Fecundity and Segregate Vigour. — By Segre- 

 gate Fecundity I mean neither Segregation produced by Fecun- 

 dity nor Fecundity produced by Segregation, but the relation in 

 which species or varieties stand to each other when the intergen- 

 eration of members of the same species or variety results in 

 higher fertility than the crossing of different species or varieties. 

 In like manner Segregate Vigour is the relation in which species 

 or varieties stand to each other when the intergeneration of 

 members of the same species or variety produces offspring more 

 vigorous than those produced by crossing with other species or 

 varieties. Integrate Fecundity and Integrate Vigour are the 

 terms by which I indicate the relation to each other of forms in 

 which the highest fertility and vigour are produced by crossing, 

 and not by independent generation. 



Before discussing these principles through which the influence 

 of Segregation is greatly increased, it will be an advantage if we 

 can gain some idea of the nature of Cumulative Fertility in its 

 relations to a law of still wider import. I refer to the fourfold law 

 of antagonistic increase and mutual limitation between (1) In- 

 tegration, (2) Segregation, (3) Adaptation, (4) Multiplication — 

 in other words between (1) General invigoration and power of 

 variation through crossing, (2) The opening of new opportunities 

 and independent possibilities, (3) Special adaptation to present 

 circumstances, (4) Powers of multiplied individualization. Darwin 

 has considered at length the 1st and the 3rd, though I do not 

 remember that he has anywhere pointed out that their develop- 

 ment is due to a kind of self-augmentation. I believe this is so 

 emphatically the case that the former might well be called the 

 law of Self-Cumulative Vigour, and the latter the law of Self- 

 Cumulative Adaptation. Corresponding to these two laws, I 

 find the additional laws of Self- Cumulative Segregation and Self- 

 Cumulative Fertility, Darwin's theory, that Diversity of Natural 

 Selection is directly and necessarily dependent on exposure to 

 different external conditions, tends to obscure, though not to 

 deny, the fact that the breeding together of the better adapted, 

 which causes the increase of adaptation, is due to the difterent 

 degrees of endowment in the organism, rather than to diversity 

 in the environment. It is also true of segregative endowment 

 and of fertility that they are necessarily cumulative whenever 



