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 a fly-brush in hoofed animals, or as an aid to
springing in the kangaroo or as a climbing organ; it will require quite
different reflex-mechanisms and nerve-combinations in the motor centres.

I used this example in order to show how unnecessary it is to assume a
special internal evolutionary power for the phylogenesis of species, for
this whole order of whales is, so to speak, MADE UP OF ADAPTATIONS; it
deviates in many essential respects from the usual mammalian type, and all
the deviations are adaptations to aquatic life. But if precisely the most
essential features of the organisation thus depend upon adaptation, what is
left for a phyletic force to do, since it is these essential features of
the structure it would have to determine? There are few people now who
believe in a phyletic evolutionary power, which is not made up of the
forces known to us--adaptation and heredity--but the conviction that EVERY