86 VISION. 
so called at all; that the animals supposed to be 
its nearest invertebrate allies have only eyes of an 
imperfect description incapable of true vision, while 
other vertebrates have eyes which repeat the land- 
scape, and are only comparable with invertebrate 
eyes in the manner mentioned. 
But however interesting the evolutions of the 
organ of vision may be, it may be questioned if 
there is not even more food for reflection in the 
very existence of such a sense as vision or such 
a sense as sound. One has no difficulty in agree- 
ing with Gegenbaur that certain eyes may have 
been evolved out of tactile organs, but it is much 
harder to understand how it comes to pass that 
touch is the sense which it is, or that there can 
possibly be any transition from touch to hearing, 
or from touch to vision. As sensations they are, 
as already said, incomparable, and intermediates 
between them are therefore inconceivable to us. 
No doubt the sensations of sound and vision are 
themselves inconceivable to those who are born 
deaf and blind, but that very consideration points 
to this: that in these senses there are two things for 
consideration, the material apparatus and the pro- 
perties of that consciousness which is capable of 
being modified by stimuli received through the 
medium of the apparatus. To me it appears plain 
