230 
KEY. J. T. GULICK ON DIVERGENT EVOLUTION 
(c) Spatial Segregation 
is Segregation arising from the relations in which the organism 
stands to space. 
I distinguish two forms, viz. Geographical and Local Segre- 
gation. 
Geographical Segregation is Segregation that arises from the 
distribution of the species in districts separated by geographical 
barriers that prevent free interbreeding. Decided differences of 
climate in neighbouring districts and regions may be classed as 
geographical barriers. 
Local Segregation is Segregation that arises when a species 
with small powers of migration and small opportunities for trans- 
portation has been, in time, very widely distributed over an area 
that is not subdivided by geographical barriers. The Segrega- 
tion in this case is due to the disproportion between the size of 
the area occupied and the powers of communication existing 
between the members of the species occupying the different parts 
of the area. Though it is often difficult to say whether a given 
case of Segregation should be classed as Geographical or Local, 
still the distinction will be found useful; for the results will 
differ according as the Segregation is chiefly due to barriers or 
to wide diffusion of the species. In Geographical Segregation 
the result is usually the development of well-defined varieties or 
species on opposite sides of the barriers ; but in Local Segrega- 
tion it often happens that the forms found in any given locality 
are connected with those in suiToimding localities by individuals 
presenting every shade of intermediate character ; and in general 
terms it may be said that the forms most widely separated in 
space are most widely divergent in character. It is of course 
apparent that when the divergence has reached a certain point 
the differentiated forms may occupy the same districts without 
interbreeding, for they will be kept apart by some, if not all, of 
the different forms of Industrial, Chronal, Conjunctional, and 
Impregnational Segregation. 
Three different forms of Spatial Segregation may be distin- 
guished according to the causes by which they are produced, viz.: — 
6. Migrational Segregation , caused by powers of locomotion 
in the organism. 
7. Transport ational Segregation , caused by activities in the 
environment that distribute the organism in different districts, 
(prominent among these are currents of atmosphere and of 
