575
Mr. Spencer had asked himself whether the direct action
of the environment, combined with the inherited effect of
function and other transforming causes, could have brought
about the differentiations just referred to, he would not
have needed to go to Natural Selection for an explanation.
It is evidently the opinion of Mr. Balfour that the
formation of pigment cells, in certain parts of the surface,
is the immediate cause of the special susceptibility of
those parts to light. And if we argued from analogy, we
might assume that the otoliths played a similar part in
creating a special local susceptibility to sound. In these
cases the organism and the environment act upon one
another without the aid of Natural Selection. Again, it
is the opinion of Mr. Balfour that the primordial filaments
of protoplasm performed the double function of muscles
and nerves ; but that in course of time some portions only
performed the function of nerves and lost their contrac
tility, while other portions performed the function of
contractility and lost their nervous power. But if this
is so, we have here an illustration of the differentiating
effects of inherited use and disuse ; and again there is no
need for the introduction of Natural Selection.
Mr. Spencer maintains that Natural Selection would
lead to the removal of the sensitive organ from the sur
face to the inside. But the surface of an organism must
always remain the means of communication with the
external world. What took place was not the removal
of a highly sensitive organ from the outside to the inside,
but the gradual concentration of a certain susceptibility
to a particular portion of the surface ; the communication
of the influence to the interior of the organism by the
means of nerves ; and the interposition between the en
vironment and the sensitive nerves of a more and more
perfect organ of sight. But behind this organ and in