ble case, the case
of the Cuckoo. The male, after having established himself, utters his
call persistently from the day of arrival until approximately the middle
of June; but, in contrast with the large majority of species, the female
has a characteristic call which she, too, utters at frequent intervals.
The female is polyandrous and has a sphere of influence embracing the
territories of a number of males; she wanders from place to place, is
often silent, and not unfrequently is engaged in dealing with her egg or
in searching for a nest in which to deposit it, and therefore she is not
always in touch with a male, still less with any particular one. Now
there is much evidence to show that the discharge of the sexual function
amongst birds is subject to control, and that this control operates
through the female--through her physiological state becoming
susceptible to stimulation only at certain periods. So that we have
these considerations, that the female is polyandrous, that she has a
territory distinct from that of the male, and that her sexual impulse is
periodical; and the further consideration that the impulse, since it is
periodical, is of limited duration and must receive immediate
satisfaction. Such being the circumstances of the case, would the voice
of the male serve to insure the union of the sexes at the appropriate
moment? Well, the fact that she is polyandrous implies that every male
in her sphere of influence is not always capable of satisfying her
sexual instinct. Is, then, the male's call an indication of his
readiness to yield to stimulation? Without a doubt it is an index of the
general physiological state which generates the sexual impulse, without
a doubt it denotes a general preparedness to breed, but there is no
evidence to show that it denotes the degree of ardour of the male at any
particular moment, and much that proves the contrary. So that only by
the female producing some special sound which will attract the males
that are eager and bring them rapidly to the spot where she happens to
be, only thus is it possible to insure the consummation of the sexual
act. This, it seems to me, is the purpose of the peculiar call of the
female--a call which, so far as biological interpretation is concerned,
is just as much a song as the melody of the Marsh-Warbler--and its
interest for us just now lies in this, that here we have a special case
in which the sexes have separate territories, the female is polyan