HUMMING-BIRDS. 141 



both sexes, whereas in the two species peculiar to the 

 islands the males are red or reddish-brown, and the 

 females green. The two red males differ very slightly 

 from each other, but the three green females differ con- 

 siderably ; and the curious point is, that the female in 

 the smaller and more distant island somewhat resembles 

 the same sex in Chili, while the female of the Juan 

 Fernandez species is very distinct, although the males of 

 the two islands are so much alike. As this forms a 

 comparatively simple case of the action of the laws of 

 variation and natural selection, it will be instructive to 

 see if we can picture to ourselves the process by which 

 the changes have been brought about. We must first 

 go back to an unknown but rather remote period, just 

 before any humming-birds had reached these islands. 

 At that time a species of this peculiar genus, Eustephanus, 

 must have inhabited Chili ; but we must not be sure 

 that it was identically the same as that which is now 

 found there, because we know that species are always 

 undergoing change to a greater or less degree. After 

 perhaps many failures, one or more pairs of the Chilian 

 bird got blown across to Juan Fernandez, and finding 

 the country favourable, with plenty of forests and a fair 

 abundance of flowers and insects, they rapidly increased 

 and permanently established themselves on the island. 

 They soon began to change colour, however, the male 

 getting a tinge of reddish-brown, which gradually 

 deepened into the fine colour nqw exhibited by the two 

 insular species, while the female, more slowly, changed 

 to white on the under-surface and on the tail, while the 

 breast-spots became more brilliant. When the change 

 of colour was completed in the male, but only partially 



