27 EEV. J. T. GTJLICK ON DIVERGENT EVOLUTION 



iu the case of organisms whose fertilizing elements are distributed 

 by wind and water, the qualities that produce these negative 

 forms of Segregation are usually accompanied by those that pro- 

 duce Prepotential Segregation, which is in an important degree 

 positive. But even Prepotential Segregation, when produced by 

 mutual incompatibility between a few individuals and a numerous 

 parent stock, depends for its continuance and development on 

 Local, Grerininal, or Floral Segregation, partially securing the 

 intergeneration of the few that are mutually compatible. On 

 the one hand, Impregnational Segregation depends on some 

 degree of Local, Grerminal, or Ploral Segregation which is a con- 

 stant feature in most species ; but, on the other hand, not only 

 do these initial forms of Positive Segregation fail of producing 

 any permanent divergence till associated with Impregnational 

 Segregation, but the more effective forms of Positive Segregation, 

 such as Industrial, Chronal, Fertilizational, Sexual, and Social 

 Segregation, often depend on Impregnational Segregation, inas- 

 much as the divergence of endowments which produces these 

 depends on Impregnational Segregation. Moreover, in all such 

 cases, increasing degrees of diversity in the forms of adaptation, 

 and consequently of diversity in the forms of natural selection, 

 must also depend upon these negative factors, which in their 

 turn depend on the weak, initial forms of Positive Segregation . 



Divergent evolution always depends on some degree of Posi- 

 tive Segregation, but not always on Negative Segregation. 

 Under Positive Segregation of a rigorous form (as, for example, 

 complete Geographical Segregation), considerable divergence may 

 result without any sexual incompatibility. Darwin has shown, 

 by careful experiments, that Integrate Vigour and Fecundity is 

 the relation in which tlie varieties of one species usually stand to 

 each other. This fact does not, however, prove that the more 

 strongly divergent forms, called species, which are prevented from 

 coalescing by Segregate Vigour and Fecundity, did not acquire 

 some degree of this latter character before any permanent diver- 

 gence of form was acquired. Their having acquired this segre- 

 gating characteristic may be the very reason why their forms are 

 now so decidedly different, for without it they would have been 

 swallowed up by the incoming waves of intergeneration. Again, 

 we must remember that forms only moderately divergent are 

 habitually classed as different species if they are separated by 

 Segregate Vigour and Fecundity (that is by some degree of 



