The Descent of Man

surrounding zone, which latter is thus rendered
lighter; and, on the other hand, that a white
spot is often formed by the colour being driven
away from a central point, so that it accumulates
in a surrounding darker zone. In either case
an ocellus is the result. The colouring matter
seems to be a nearly constant quantity, but is
redistributed, either centripetally or centrifugally.
The feathers of the common guinea-fowl
offer a good instance of white spots surrounded
by darker zones; and wherever the white spots
are large and stand near each other, the surrounding
dark zones become confluent. In the
same wing-feather of the Argus pheasant dark
spots may be seen surrounded by a pale zone,
and white spots by a dark zone. Thus the formation
of an ocellus in its most elementary state
appears to be a simple affair. By what further
steps the more complex ocelli, which are surrounded
by many successive zones of colour,
have been generated, I will not pretend to say.
But the zoned feathers of the mongrels from