_Juan Fernandez._--This island is situated in the Pacific Ocean, about 400 miles west of Valparaiso in Chili. It is only a few miles in extent, yet it possesses four land-birds, excluding the powerful Accipitres. These are _Turdus falklandicus_; _Anæretes {50}fernandensis_, one of the Tyrannidæ; and two humming-birds, _Eustephanus fernandensis_ and _E. galeritus_. The first is a widespread South Temperate species, the two next are peculiar to the island, while the last is a Chilian species which ranges south to Tierra del Fuego. But ninety miles beyond this island lies another, called "Mas-a-fuero," very much smaller; yet this, too, contains four species of similar birds; one, _Oxyurus mas-a-fueræ_, allied to the wide-spread South Temperate _O. spinicauda_, and _Cinclodes fusus_, a South Temperate species--both Dendrocolaptidæ; with a humming-bird, _Eustephanus leyboldi_, allied to the species in the larger island. The preceding facts are taken from papers by Mr. Sclater in the _Ibis_ for 1871, and a later one in the same journal by Mr. Salvin (1875). The former author has some interesting remarks on the three species of humming-birds of the genus _Eustephanus_, above referred to. The Chilian species, _E. galeritus_, is green in both sexes. _E. fernandensis_ has the male of a fine red colour and the female green, though differently marked from the female of _E. galeritus_. _E. leyboldi_ (of Mas-a-fuera) has the male also red and the female green, but the female is more like that of _E. galeritus_, than it is like the female of its nearer ally in Juan Fernandez. Mr. Sclater supposes, that the ancient parent form of these three birds had the sexes alike, as in the present Chilian bird; that a pair (or a female having fertilised ova) reached Juan Fernandez and colonised it. Under the action of sexual selection (unchecked by some conditions which had impaired its efficacy on the continent) the male gradually assumed a brilliant plumage, and the female also slightly changed its markings. Before this change was completed the bird had established an isolated colony on Mas-a-fuera; and here the process of change was continued in the male, but from some unknown cause checked in the female, which thus remains nearer the parent form. Lastly the slightly modified Chilian bird again reached Juan Fernandez and exists there side by side with its strangely altered cousin.