External and Internal Factors in Evolution 317 



increase, yet they differ conspicuously in their small size from 

 the wild English rabbit. ... In color the Porto Santo 

 rabbit differs considerably from the common rabbit ; the 

 upper surface is redder, and is rarely interspersed with any 

 black or black-tipped hairs. The throat and certain parts of 

 the under surface, instead of being pure white, are generally 

 gray or leaden color. But the most remarkable difference 

 is in the ears and tail. I have examined many fresh English 

 rabbits, and the large collection of skins in the British Museum 

 from various countries, and all have the upper surface of the 

 tail and the tips of the ears clothed with blackish gray fur ; 

 and this is given in most works as one of the specific char- 

 acters of the rabbit. Now in the seven Porto Santo rabbits 

 the upper surface of the tail was reddish brown, and the tips 

 of the ears had no trace of the black edging. But here we 

 meet with a singular circumstance: in June, 1861, I examined 

 two of these rabbits recently sent to the Zoological Gardens 

 and their tails and ears were colored as just described ; but 

 when one of their dead bodies was sent to me in February, 1863, 

 the ears were plainly edged, and the upper surface of the tail 

 was covered with blackish gray fur, and the whole body was 

 much less red ; so that under the English climate this individ- 

 ual rabbit had recovered the proper color of its fur in rather 

 less than four years." 



Another striking case of sudden variation is found in the 

 peacock. It is all the more remarkable because this bird has 

 hardly varied at all under domestication, and is almost exactly 

 like the wild species living in India to-day. Darwin states : 

 "There is one strange fact with respect to the peacock, 

 namely, the occasional appearance in England of the 'ja- 

 panned' or 'black-shouldered' kind. This form has lately 

 been named, on the high authority of Mr. Slater, as a distinct 

 species, viz. Pavo nigripennis, which he believes will here- 

 after be found wild in some country, but not in India, where 

 it is certainly unknown. The males of these japanned birds 



