nts
are commonly ejected from the nest within three days after the cuckoo is
hatched; and as the latter at this age is in a most helpless condition,
Mr. Gould was formerly inclined to believe that the act of ejection was
performed by the foster-parents themselves. But he has now received a
trustworthy account of a young cuckoo which was actually seen, while
still blind and not able even to hold up its own head, in the act of
ejecting its foster-brothers. One of these was replaced in the nest by
the observer, and was again thrown out. With respect to the means by
which this strange and odious instinct was acquired, if it were of great
importance for the young cuckoo, as is probably the case, to receive as
much food as possible soon after birth, I can see no special difficulty
in its having gradually acquired, during successive generations, the
blind desire, the strength, and structure necessary for the work of
ejection; for those cuckoos which had such habits and structure best
developed would be the most securely reared. The first step towards the
acquisition of the proper instinct might have been mere unintentional
restlessness on the part of the young bird, when somewhat advanced
in age and strength; the habit having been afterwards improved, and
transmitted to an earlier age. I can see no more difficulty in this than
in the unhatched young of other birds acquiring the instinct to break
through their own shells; or than in young snakes acquiring in their
upper jaws, as Owen has remarked, a transitory sharp tooth for cutting
through the tough egg-shell. For if each part is liable to individual
variations at all ages, and the variations tend to be inherited at
a corresponding or earlier age--propositions which cannot be
disputed--then the instincts and structure of the young could be slowly
modified as surely as those of the adult; and both cases must stand or
fall together with the whole theory of natural selection.

Some species of Molothrus, a widely distinct genus of American birds,
allied to our starlings, have parasitic habits like those of the cuckoo;
and the species present an interesting gradation in the perfection
of their instincts. The sexes of Molothrus badius are stated by an
excellent observer, Mr. Hudson, sometimes to live promiscuously together
in flocks, and sometimes to pair. They either build a nest of their own
or seize on one belonging to some other bird, occasionally throwing out
the nestlings of