DISTRIBUTION OF FAUNA AND FLORA. 1 2Q 



7. Location of least dependence upon a restricted habitat. 



8. Continuity and directness of individual variations or modifi- 

 cations radiating from the center of origin along the highways of 

 dispersal. 



9. Direction indicated by biogeographical affinities. 



10. Direction indicated by annual migration in birds. (Palmen.) 

 Sixth. There are three primary outlets of dispersal from the 



Southeast : 



1. The Mississippi Valley and its tributaries. 



2. The Coastal Plain. 



3. The Appalachian Mountains and adjacent plateaus. 



The first two have also functioned for tropical types, and the 

 third for boreal forms. Dispersal is both forward and backward 

 along these highways. 



Seventh. The individual variations of animals and plants, such 

 as size, productiveness, continuity of variation, color variation, 

 and change of habit and habitats, should be studied along their 

 lines of dispersal and divergence from their center of origin. Life 

 areas should be studied as centers of dispersal and origin, and 



hence dynamically and genetically. 

 HULL ZOOLOGICAL LABORATORY, 



UNIVERSITY OF CHICAGO, December, 1901. 



REFERENCES. 

 Allen, J. A. 



'71 On the Mammals and Winter Birds of East Florida, with an Examination of 

 Certain Assumed Specific Characters in Birds, and a Sketch of the Bird Faunae 

 of Eastern North America. Bull. Mus. Comp. Zool., Vol. II., No. 3, pp. 

 161-450. 



'72 Geographical Variation in North American Birds. Proc. Bost. Soc. Nat. 

 Hist., Vol. XV., pp. 212-219. 



'74 On Geographical Variation in Color Among North American Squirrels ; 

 with a list of species and varieties of American Sciuridee occurring north of 

 Mexico. Proc. Bost. Soc. Nat. Hist., Vol. XVI., pp. 276-294. 



'76 Geographical Variation Among North American Mammals, especially in 

 respect to size. Bull. U. S. Geol. and Geogr. Survey of the Terr. (Harden), 

 Vol. II., No. 4, pp. 309-344. 



'77 The Influence of Physical Conditions on the Genesis of Species. Radical Re- 

 view, Vol. I., pp. 108-140. 



'92 Variations in Vertebrated Animals. Amer. Nat., Vol. XXVI., pp. 86-89. 

 Bessey, C. E. 



'92 A Preliminary Report on the Native Trees and Shrubs of Nebraska. Bull. 

 Agric. Exp. Stat. of Neb., Vol. IV., No. 4, pp. 1-32. 



