Geographical Distribution. 175 



of old ones, are not ordinarily by zigzag and meandering paths, 

 but by relatively straight ones ; and though, of course, a path 

 once taken may be diverged from, yet in such a case it is not 

 regained. This applies particularly to the organism as a whole; 

 in minor details more latitude is permissible." 



(c) " Parallelism and convergence of development are much 

 more general and important modes of evolution than is com- 

 monly supposed. By parallelism is meant the independent 

 acquisition of similar structures in forms which are themselves 

 nearly related, and by convergence such acquisition in forms 

 which are not closely related, and thus in one or more respects 

 come to be more nearly alike than were their ancestors." 



Chapter XIII. 

 Geographical Distribution. 



Zoo-geographical Regions Phyto-geographical Regions Factors in Dis- 

 tribution The Great Faunas and Floras : Littoral, Pelagial, 

 Abyssal, Fluvial, Terrestrial Evolution of Faunas. 



Although various naturalists from Pliny to Buffon 

 seem to have been impressed by certain outstanding* 

 facts concerning the geographical distribution of living 

 creatures, the serious study of the subject hardly began 

 before the Darwinian era. There was collecting of 

 material and an occasional attempt to group plants and 

 animals in geographical regions, but the significance 

 of the problem could not be perceived without the light 

 of the evolution idea. The main problem is to find out 

 the causes of the existing distribution, to discover the 

 factors which determine why certain organisms are here 

 and not there, and others there and not here; but it is 

 evident that the problem does not press upon the non- 

 evolutionist. 



Following a short history of zoo-geography by Dr. 

 Arnold E. Ortmann, we may distinguish Zoo 

 various periods of inquiry into the regions graphical 

 of distribution. 



A. Wagner seems to have been the first (1844-1846) 

 to attempt any systematization of the mass of materials 



