308 RIVERBY 



hints and suggestions of it, or, as it were, prelimi- 

 nary studies of it, in other allied species. I am not 

 thinking of the law of evolution which binds together 

 the animal life of the globe, but of a kind of over- 

 flow in nature which carries any marked endowment 

 or characteristic of a species in lessened force or com- 

 pletion 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 suc- 

 ceeding type a kind of lateral and secondary evolu- 

 tion. Thus there are progressive series among our 

 song-birds. The brown thrasher is an advance upon 

 the catbird, and the mockingbird is an advance upon 

 the brown thrasher in the same direction. Each one 

 carries the special gift of song or mimicking some 

 stages forward. The same among the larks, through 

 the so-called meadowlark and the shore lark, up to 

 the crowning triumph of the skylark. The night- 

 ingale also finishes a series which starts with the 

 hedge warbler and includes the robin redbreast. 

 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 walk- 

 ing fish of tropical America, or the tree-climbing fish 

 of India. Prom the protective coloring of certain 

 insects, animals, and birds, the step is not far to 

 actual mimicry of certain special forms and colors. 



