se
circumstances, reach a higher level of intensity, and let us see how
this will add to the security of the territory. The fact that the male
has established itself and obtained a mate is not alone sufficient to
accomplish the end for which the territory has been evolved. During the
period between the initial discharge of the sexual function and the time
when incubation draws to a close, much may happen to prejudice the
future of the offspring; there is always the possibility of invasion by
an individual whose development is backward or which has been
unsuccessful in making good the first step, and, as we saw in the case
of the Reed-Bunting, a portion of the ground won may be lost; there is
always the danger of gradual encroachment by neighbouring owners; and
there is even a possibility that a pair may be so persistently harassed
by more virile neighbours as to forsake the locality permanently. If
then a male is to attain a full measure of success it must be capable
of keeping its boundaries intact up to the time when the young are able
to fend for themselves, and consequently it is important that its
intolerant nature should remain susceptible to stimulation throughout
the greater part of the season.

Does the presence of a female serve to promote this end? Now we know
very little of the influence exerted by one sex upon the other.
Professor Lloyd Morgan has suggested that the male raises the emotional
tone of the female, a suggestion which seems to me in accordance with
the facts. There is reason to believe, however, that the converse is
also true--namely that the excitement of the male reaches a higher level
of intensity when a female is present. Granting then that his emotional
tone is raised, how will this affect the question? So great is the
difference of opinion as to the part that the emotions play in
furthering the life of the individual that one hesitates to accept any
particular one. But it seems to be generally admitted that emotion adds
to the efficacy of behaviour, and this is the view of Professor Lloyd
Morgan. "Whatever may be the exact psychological nature of the emotions,
it may be regarded," he says, "as certain that they introduce into the
conscious situation elements which contribute not a little to the energy
of behaviour. They are important conditions to vigorous and sustained
conation." Therefore, if it be true that the female raises the emotional
tone of the male, the result will be an increase