The Descent of Man

generally gain a clue by comparing all the species
of the same group, if it be a large one; for
some of them will probably retain, at least partially,
traces of their former characters. Instead
of entering on tedious details respecting various
groups, in which striking instances of
gradation could be given, it seems the best plan
to take one or two strongly marked cases, for
instance that of the peacock, in order to see if
light can be thrown on the steps by which this
bird bas become so splendidly decorated. The
peacock is chiefly remarkable from the extraordinary
length of his tail-coverts; the tail itself
not being much elongated. The barbs along
nearly the whole length of these feathers stand
separate or are decomposed; but this is the case
with the feathers of many species, and with
some varieties of the domestic fowl and pigeon.
The barbs coalesce towards the extremity of the
shaft forming the oval disc or ocellus, which is
certainly one of the most beautiful objects in the
world. It consists of an iridescent, intensely