s apparatus necessary for its automatic
regulation. All instincts depend upon compound reflex mechanisms and are
just as indispensable as the parts they have to set in motion, and all
may have arisen through processes of selection if the reasons which I
have elsewhere given for this view are correct. ("The Evolution Theory",
London, 1904, page 144.)

Thus there is no lack of adaptations within the organism, and
particularly in its most important and complicated parts, so that we may
say that there is no actively functional organ that has not undergone a
process of adaptation relative to its function and the requirements of
the organism. Not only is every gland structurally adapted, down to the
very minutest histological details, to its function, but the function
is equally minutely adapted to the needs of the body. Every cell in the
mucous lining of the intestine is exactly regulated in its relation to
the different nutritive substances, and behaves in quite a different way
towards the fats, and towards nitrogenous substances, or peptones.

I have elsewhere called attention to the many adaptations of the whale
to the surrounding medium, and have pointed out--what has long been
known, but is not universally admitted, even now--that in it a great
number of important organs have been transformed in adaptation to the
peculiar conditions of aquatic life, although the ancestors of the whale
must have lived, like other hair-covered mammals, on land. I cited a
number of these transformations--the fish-like form of the body, the
hairlessness of the skin, the transformation of the fore-limbs to fins,
the disappearance of the hind-limbs and the development of a tail fin,
the layer of blubber under the skin, which affords the protection
from cold necessary to a warm-blooded animal, the disappearance of the
ear-muscles and the auditory passages, the displacement of the external
nares to the forehead for the greater security of the breathing-hole
during the brief appearance at the surface, and certain remarkable
changes in the respiratory and circulatory organs which enable the
animal to remain for a long time under water. I might have added many
more, for the list of adaptations in the whale to aquatic life is by no
means exhausted; they are found in the histological structure and in the
minutest combinations in the nervous system. For it is obvious that a
tail-fin must be used in quite a different way from a tail, which serves
as