Land-birds of Juan Fernandez. 183 



of how it may come to pass that two re))rescntative species may 

 coexist in the same area. The original colony of E. galeritus, 

 or rather of the Eustephanus priscus, from which all existing 

 Eustephani are descended, arrived in Juan Fernandez with the 

 green plumage which, at that period, clothed both sexes of E. 

 galeritus and the females of E. fernandensis and E. leyboldi. 

 Natural selection or the " vis Darwiniana," as we may call it (to 

 which, according to Mr. Mivart, some other unknown vis, the 

 vis Mivartiana, must be added), set to work, especially on the 

 male, and converted him into the brilliant red bird which he 

 now is, leaving the female scarcely changed. During this pe- 

 riod no fresh arrivals of the parent form, at any rate none of 

 importance, could have taken place, or the operation of the vis 

 Darwiniana on the male Eustephanus could hardly have pro- 

 duced any result. Within recent times, howevei*, there has 

 been a fresh irruption of Eustephanus galeritus from the neigh- 

 bouring mainland; and we have thus both representative spe- 

 cies now coexisting within the same area. 



Mas-afuera must have received its colony of Eustephani from 

 Mas-a-tierra after the male E. fernandensis had become red, but 

 before the female had deviated so far from the parent form as 

 she now does. Otherwise we cannot account for the female of 

 E. leyboldi being more like E. galeritus than the female of E. 

 fernandensis. 



From all that has been before stated it will be obvious that, 

 so far as we can judge from our present knowledge of the ter- 

 restrial avifauna of the Juan Fernandez group of islands, the 

 following conclusions may be drawn. 



1. The Juan Fernandez group belongs strictly, so far as its 

 avifauna is concerned, to the Chilian or Patagoniah division of 

 the Neotropical Region. 



2. All the species known to occur in it are either identical 

 with, or closely allied representatives of, Chilian forms. 



3. The Juan Fernandez islands have been peopled with hfe 

 within a comparatively recent period, by immigration from the 

 adjoining mainland of Chili. 



