APPENDIX I. 
REFLEXIVE SEGREGATION.* 
{A small portion of ‘‘ Divergent Evolution through Cumulative Segregation.’’] T 
Reflexive segregation is segregation arising from the relations in 
which the members of one species stand to each other. 
It includes three classes, which I call ‘‘conjunctional,” ‘‘impregna- 
tional,” and ‘‘institutional segregation.”’ 
It is important to observe that intergeneration requires compati- 
bility between members of the group in all the circle of relations in 
which the organism stands; but, in order to insure isolation between 
any two or more sections of a species, it is sufficient that incompati- 
bility should exist at but one point. If either sexual or social 
instincts do not accord, if structural or dimensional characters are not 
correlated, if the sexual elements are not mutually potential, or if 
fixed institutions hold groups apart, intergeneration is obstructed or 
prevented and isolation is the result, either as segregation or as sepa- 
ration that is gradually transformed into segregation. 
(a) CONJUNCTIONAL SEGREGATION. 
Conjunctional segregation is segregation arising from the instincts 
by which organisms seek each other and hold together in more or less 
compact communities, or from the powers of growth and segmentation 
in connection with self-fertilization, through which similar results are 
gained. 
I distinguish four forms—social, sexual, germinal, and floral segre- 
gation. 

* Under ‘‘ Demarcational Segregation”’ I class the influences by which organ- 
isms are distributed in separate groups. It includes both environal segregation 
and reflexive segregation, and is equivalent to isolation as now generally used. In 
the section of this paper on Environal Segregation (not here reproduced), I 
considered the forms of isolation arising from the relations of the species to the 
environment. A classified table of the forms of segregation will be found near 
the end of this paper. 
t+ Read December 15, 1887. From the Linnean Society’s Journal, Zodlogy, 
Vol XX. 
159 
