116 ZOOLOGICAL PHILOSOPHY 



Even in the class of mammals, comprising the most perfect animals, 

 where the vertebrate plan of organisation is carried to its highest 

 completion, not only is the right-whale devoid of teeth, but the 

 ant-eater (Myrmecophaga) is also found to be in the same condition, 

 since it has acquired a habit of carrying out no mastication, and has 

 long preserved this habit in its race. 



Eyes in the head are characteristic of a great number of different 

 animals, and essentially constitute a part of the plan of organisation 

 of the vertebrates. 



Yet the mole, whose habits require a very small use of sight, has 

 only minute and hardly visible eyes, because it uses that organ so 

 little. 



Olivier's Spalax (Voyage en Egypte et en Perse), which lives under- 

 ground like the mole, and is apparently exposed to dayhght even less 

 than the mole, has altogether lost the use of sight : so that it shows 

 nothing more than vestiges of this organ. Even these vestiges are 

 entirely hidden under the skin and other parts, which cover them up 

 and do not leave the shghtest access to light. 



The Proteus, an aquatic reptile alhed to the salamanders, and living 

 in deep dark caves under the water, has, like the Spalax, only vestiges 

 of the organ of sight, vestiges which are covered up and hidden in the 

 same way. 



The following consideration is decisive on the question which I 

 am now discussing. 



Light does not penetrate everywhere ; consequently animals which 

 habitually live in places where it does not penetrate, have no oppor- 

 tunity of exercising their organ of sight, if nature has endowed 

 them with one. Now animals belonging to a plan of organisation of 

 which eyes were a necessary part, must have originally had them. 

 Since, however, there are found among them some which have lost 

 the use of this organ and which show nothing more than hidden and 

 covered up vestiges of them, it becomes clear that the shrinkage and 

 even disappearance of the organ in question are the results of a per- 

 manent disuse of that organ. 



This is proved by the fact that the organ of hearing is never in this 

 condition, but is always found in animals whose organisation is of the 

 kind that includes it : and for the following reason. 



The substance of sound, ^ that namely which, when set in motion by 

 the shock or the vibration of bodies, transmits to the organ of hearing 



^ Physicists believe and even afiSrm that the atmospheric air is the actual sub- 

 stance of sound, that is to say, that it is the substance which, when set in motion 

 by the shocks or vibrations of bodies, transmits to the organ of hearing the impression 

 of the concussions received. 



That this is an error is attested by many known facts, showing that it is impossible 



