n6 DARWINISM TO-DAY. 



related species differ widely in their ornamental plumage, 



that this should be attributed to a difference in 



Problem of preference among the females of the related 



the Andean . & . 



humming-birds, species. The humming-bird, Schist es perso- 

 natus, lives in Ecuador on the west side of the 

 Andes, in a restricted range of four degrees of latitude. It 

 is distinguished from the nearly related Schist es geoffroyi 

 .especially in the possession by its male of a brilliant spot over 

 each eye. Schist es geoffroyi lives on the east side of the 

 Andes from Colombia to Central Peru, with a range cover- 

 ing over twenty degrees of latitude, which range is divided 

 into two completely separated regions by the Marafion 

 valley. Now if isolation alone is sufficient to produce a 

 change in the taste of the females, one would expect to find 

 two sorts of males (as far as ornamental pattern goes) in- 

 side this one species. But there is but one kind of male 

 through the whole range. Why is the taste of the female 

 constant through twenty degrees of latitude, while it is 

 changed on the other side of the Andes in a limited range 

 of four degrees of latitude? Another case presented by 

 Stolzmann is even more striking. The Chilian hummer, 

 Eustephanns galeritus, which is green in both sexes, has 

 migrated from the continent to the Juan Fernandez Islands. 

 On Masatierra Island it has changed to Bust, fernandensis, 

 in Masafuera Island to Eust. leyboldi. These two species 

 agree in the females with the original continental form 

 (that is, are green) while the males have become red, but in 

 different pattern in the two species. Eust. galeritus (the 

 Continental form) also occurs on Masatierra Island, in the 

 same form as on the continent, that is, with green male. 

 Now one must presume from this state of affairs that_this 

 species (galeritus) has been able to reach Masatierra twice, 

 once long ago the descendants of the invasion having 

 changed to Eust. fernandensis and once more recently 

 the descendants of these later migrants showing as yet no 



