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 
