al that they are performed, whether or not of any service,
whenever the same desire or sensation is felt, even in a very weak
degree." (Ibid. page 368.) The modes of expression which fall under
this head have become instinctive through the hereditary transmission of
acquired habit. "As far as we can judge, only a few expressive movements
are learnt by each individual; that is, were consciously and voluntarily
performed during the early years of life for some definite object, or in
imitation of others, and then became habitual. The far greater number of
the movements of expression, and all the more important ones, are innate
or inherited; and such cannot be said to depend on the will of the
individual. Nevertheless, all those included under our first principle
were at first voluntarily performed for a definite object,--namely,
to escape some danger, to relieve some distress, or to gratify some
desire." (Ibid. pages 373, 374.)

"Our second principle is that of antithesis. The habit of voluntarily
performing opposite movements under opposite impulses has become firmly
established in us by the practice of our whole lives. Hence, if certain
actions have been regularly performed, in accordance with our first
principle, under a certain frame of mind, there will be a strong and
involuntary tendency to the performance of directly opposite actions,
whether or not these are of any use, under the excitement of an opposite
frame of mind." ("Expression of the Emotions", page 368.) This principle
of antithesis has not been widely accepted. Nor is Darwin's own position
easy to grasp.

"Our third principle," he says (Ibid. page 369.), "is the direct action
of the excited nervous system on the body, independently of the will,
and independently, in large part, of habit. Experience shows that
nerve-force is generated and set free whenever the cerebro-spinal system
is excited. The direction which this nerve-force follows is necessarily
determined by the lines of connection between the nerve-cells, with each
other and with various parts of the body."

Lack of space prevents our following up the details of Darwin's
treatment of expression. Whether we accept or do not accept his three
principles of explanation we must regard his work as a masterpiece of
descriptive analysis, packed full of observations possessing lasting
value. For a further development of the subject it is essential that
the instinctive factors in expression should be more