TALKS WITH YOUNG OBSERVERS 311 



you find any marked trait or gift in a species 

 you will find hints and suggestions of it, or as 

 it Avere, preliminary studies of it, in other allied 

 species. I am not thinking of the law of evo- 

 lution which binds together the animal life of 

 the globe, but of a kind of overflow in nature 

 which carries any marked endowment or charac- 

 teristic of a species in lessened force or comple- 

 tion to other surrounding species. Or if looked 

 at from the other way, a progressive series, the 

 idea being more and more fully carried out in 

 each succeeding type — a kind of lateral and 

 secondary evolution. Thus there are progres- 

 sive series among our song-birds. The brown 

 thrasher is an advance upon the catbird and the 

 mocking bird is an advance upon the brown 

 thrasher in the same direction. Each one car- 

 ries the special gift of song or mimicking some 

 stages forward. The same among the larks, 

 through the titlark, shore-lark, up to the crown- 

 ing triumph of the skylark. The nightingale 

 also finishes a series Avhich starts with the 

 hedge warbler, and includes the robin red- 

 breast. Our ground- sparrow songs probably 

 reach their highest perfection in the song of the 

 fox-sparrow; our finches in that of the purple 

 finch, etc. 



The same thing may be observed in other 

 fields. The idea of the flying fish, the fish that 

 leaves the water and takes for a moment to the 

 air, does not seem to have exhausted itself till 

 we reach the walking fisli of tropical America, 

 or the tree-climbing fish of India. From the 



