APPENDIX I. 



REFLEXIVE SEGREGATION.* 



[A small portion of " Divergent Evolution through Cumulative Segregation."]! 



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, Zoology, 



Vol XX. 



159 



