l of secrecy is
as yet far from lifted; nor will it be, until we can say why it is
beneficial that the sexual elements should be differentiated to a
certain extent, and why, if the differentiation be carried still
further, injury follows." He has also shown us the way along which
to follow up this problem; it is that of carefully planned and exact
experimental research. It may be that eventually many things will be
viewed in a different light, but Darwin's investigations will always
form the foundation of Floral Biology on which the future may continue
to build.

XXI. MENTAL FACTORS IN EVOLUTION. By C. Lloyd Morgan, LL.D., F.R.S.

In developing his conception of organic evolution Charles Darwin was
of necessity brought into contact with some of the problems of mental
evolution. In "The Origin of Species" he devoted a chapter to "the
diversities of instinct and of the other mental faculties in animals of
the same class." ("Origin of Species" (6th edition), page 205.) When
he passed to the detailed consideration of "The Descent of Man", it
was part of his object to show "that there is no fundamental difference
between man and the higher mammals in their mental faculties." ("Descent
of Man" (2nd edition 1888), Vol. I. page 99; Popular edition page 99.)
"If no organic being excepting man," he said, "had possessed any mental
power, or if his powers had been of a wholly different nature from those
of the lower animals, then we should never have been able to convince
ourselves that our high faculties had been gradually developed." (Ibid.
page 99.) In his discussion of "The Expression of the Emotions" it
was important for his purpose "fully to recognise that actions readily
become associated with other actions and with various states of the
mind." ("The Expression of the Emotions" (2nd edition), page 32.) His
hypothesis of sexual selection is largely dependent upon the exercise
of choice on the part of the female and her preference for "not only the
more attractive but at the same time the more vigorous and victorious
males." ("Descent of Man", Vol. II. page 435.) Mental processes and
physiological processes were for Darwin closely correlated; and he
accepted the conclusion "that the nervous system not only regulates most
of the existing functions of the body, but has indirectly influenced
the progressive development of various bodily structures and of certain
mental qualities." (Ibid. pages 437, 438.)

Throughout his