405 



mainly to the dyin.u out <>| one md tin- evolution of 



others which take their place^. Of in lOOli < ,i <> to migration. 11 



(Shelford.) 



M.iny owe their present distribution prim.iri! 



the phenomena of the ^hu ial epoch. An excellent ex;unple of thi-is 

 the White Mountain butterfly (page 325). In Ark/ 

 the "elevation is not sullicicnt to provide true boreal conditions, but. 

 modify the temperature so that certain species, abundant at the 

 north, and forced southward during the glacial epoch, have been enabled 

 to exist in this latitude till the present time. Such are the grasshoppers 

 Tcttix hancocki, Chloealtis conspersa, and Melanoplus fasciatus." 

 (Morse.) 



"The chief biological importance of the Southeastern United States, 

 comprising Virginia, North and South Carolina, Georgia, Florida, 

 Alabama, eastern Tennessee, and West Virginia, is connected with two 

 facts: First, this region served during the Glacial Epoch as a refuge for 

 boreal forms of life which had been pushed southward by the climatal 

 conditions of the Ice Age, and at the close of that period it became the 

 center of dispersal whence these forms were able to restock the opening 

 country at the north. Second, during this later period its lowland 

 plains served, and probably continue to serve, as a highway of dispersal 

 for austral forms entering the country from the south and southwest, 

 many of which have penetrated far into the heavily glaciated region of 

 the Northern States." (Morse.) 



Seasonal. " Seasonal succession is the succession of species or 

 stages in the life histories of species over a given locality, due to heredi- 

 tary and environic differences in the life histories (time of appearance) 

 of species living there. " (Shelford.) "Successful species are those that 

 fit into the seasonal rhythm with respect to physical conditions, 

 food, and numerous other relations. " (Shelford.) 



Many examples of seasonal succession among insects will occur 

 to the student of insect life. The seasonal succession of insects is 

 frequently correlated with that of plants. The cycle of an insect may 

 be adjusted to that of a plant upon which it depends. 



Thus "the Membracidae or tree hoppers are celebrated for the 

 wonderful variety and complexity of their adaptations to their food 

 plants. . . . The tree hoppers of the genus Telamona, for example, 

 feed very largely on the sap of the trees and mainly on the tender 

 growing twigs. They find optimum conditions for such feeding only 

 during the comparatively short period in which the tree is making its 



