this instinct retained by our chickens has become useless under
domestication, for the mother-hen has almost lost by disuse the power of
flight.

Hence, we may conclude that under domestication instincts have been
acquired and natural instincts have been lost, partly by habit and partly
by man selecting and accumulating, during successive generations, peculiar
mental habits and actions, which at first appeared from what we must in our
ignorance call an accident. In some cases compulsory habit alone has
sufficed to produce inherited mental changes; in other cases compulsory
habit has done nothing, and all has been the result of selection, pursued
both methodically and unconsciously; but in most cases habit and selection
have probably concurred.

SPECIAL INSTINCTS.

We shall, perhaps, best understand how instincts in a state of nature have
become modified by selection by considering a few cases. I will select
only three, namely, the instinct which leads the cuckoo to lay her eggs in
other birds' nests; the slave-making instinct of certain ants; and the
cell-making power of the hive-bee: these two latter instincts have
generally and justly been ranked by naturalists as the most wonderful of
all known instincts.

INSTINCTS OF THE CUCKOO.

It is supposed by some naturalists that the more immediate cause of the
instinct of the cuckoo is that she lays her eggs, not daily, but at
intervals of two or three days; so that, if she were to make her own nest
and sit on her own eggs, those first laid would have to be left for some