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 



