old a saffron or red plumage. For instance, a first-rate black bantam has
been described, which during three seasons was perfectly black, but then
annually became more and more red; and it deserves notice that this
tendency to change, whenever it occurs in a bantam, "is almost certain to
prove hereditary."[90] The cuckoo or blue-mottled Dorking cock, when old,
is liable to acquire yellow or orange hackles in place of his proper
bluish-grey hackles.[91] Now, as _Gallus bankiva_ is coloured red and
orange, and as Dorking fowls and both kinds of bantams are descended from
this species, we can hardly doubt that the change which occasionally occurs
in the plumage of these birds as their age advances, results from a
tendency in the individual to revert to the primitive type.

* * * * *

_Crossing as a direct cause of Reversion._--It has long been notorious that
hybrids and mongrels often revert to both or to one of their parent-forms,
after an interval of from two to seven or eight, or according to some
authorities even a greater number of generations. But that the act of
crossing in itself gives an impulse towards reversion, as shown by the
reappearance of long-lost characters, has never, I believe, been hitherto
proved. The proof lies in certain peculiarities, which do not characterise
the immediate parents, and therefore cannot have been derived from them,
frequently appearing in the offspring of two breeds when crossed, which
peculiarities never appear, or appear with extreme rarity, in these same
breeds, as long as they are {40} precluded from crossing. As this
conclusion seems to me highly curious and novel, I will give the evidence
in detail.

My attention was first called to this subject, and I was led to make
numerous experiments, by MM. Boitard and Corbie having stated that,
when they crossed certain breeds, pigeons coloured like the wild _C.
livia_, or the common dovecot, namely, slaty-blue, with double black
wing-bars, sometimes chequered with black, white loins, the tail barred
with black, with the outer feathers edged with white, were almost
invariably produced. The breeds which I crossed, and the remarkable
results attained, have been fully described in the sixth chapter. I
selected pigeons, belonging to true and ancient breeds, which had not a
trace of blue or any of the above specified marks; but when crossed,
and their mongrels rec