through cumulative segregation. 
195 
(5) “ Separation and Variation,” that is, Variation not over- 
whelmed by crossing, “ is all that is necessary to secure a di- 
vergence of types in the descendants of one stock,” though 
external conditions remain the same, and though the Separation 
is other than geographical. 
(6) The Separation of which I speak is anything, in the 
species or in the environment, that divides the species into two 
or more sections that do not freely intercross, whether the dif- 
ferent sections remain in the original home or enter new and 
dissimilar environments. 
Though these propositions were very briefly and imperfectly 
presented, I am not aware that any better statement of the facts 
of Segregation had been previously published. 
The present paper is the result of a loug continued endeavour 
to understand the relations in which this factor stands to Natural 
Selection and the other causes that co-operate in producing 
divergent evolution ; and though my work has been done under 
the great disadvantage of entire separation from libraries, and 
from other workers in similar lines, I trust it may contribute 
something towards the elucidatiou of the subject. In expanding 
my theory I have been unable to make any use of the positions 
taken in Moritz Wagner’s paper, as they seem to me very 
extreme and far removed from the facts of nature. The two 
theories correspond chiefly in that they discuss the relation of 
Separation to the transformation of species ; while the explana- 
tions given of the nature, causes, and effects of Separation widely 
differ. I am informed that my paper on “ Diversity of Evolution 
under One Set of External Conditions ” was translated and circu- 
lated in Gfermany ; but whether it had any effect in modifying 
Wagner’s theory, I have not the means of knowing. 
I have recently discovered that the principle of Segregate 
Breeding, which I have found to be of such importance in the 
evolution of species, is allied to the law of Segregation pro- 
pounded by Spencer in his ‘ Eirst Principles.’ By direct con- 
sideration of the conditions that have been found necessary for 
the development of divergent races of domestic plants aud animals, 
I have discovered Segregate Breeding as a necessary condition for 
divergent evolution ; and by direct observation on the propaga- 
tion of plants aud animals under natural conditions, I have 
discovered Cumulative Segregation as a constant result fron- 
certain forms of activity in the organism when dealing with a 
