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