230 



REV. J. T. GTJLICK ON DIYERGENT EYOLrTION 



(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 interbreediug. 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 difi&cult to say whether a given 

 case of Segregation should be classed as Greographical or Local, 

 still the distinction will be found useful ; for the results will 

 differ according as the Segregation is chiefiy due to barriers or 

 to wide diffusion of the species. In Greographical 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 surrounding 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, Clironal, 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. Migratio7ial 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 



