On the Anatomy and Physiology of the Organs of the Senses. 21 1 



been by other means discovered, served to explain the composition of the 

 eye; and this is the reason why the eye is, and the ear is not, understood : 

 no question at all but that tlie parts composing the ear are as carefully 

 arranged, as necessary, and as subservient to hearing as those of the eye 

 are to vision, it would be contrary to analogy to conclude otherwise, but 

 the science of optics is comparatively well understood, that of acoustics 

 is not. 



But the eye and the ear rest together upon a different footing, and must 

 be considered under a very different point of view from the organs of the 

 other three senses. 



In those two there is superimposed upon the mere expanded nerve, — the 

 part essential to the whole five — an apparatus for the collection and con- 

 centration of the rays of light and waves of sound, which is as purely 

 mechanical as the object glass of an achromatic telescope, or a hearing 

 trumpet ; and capable, when injured, of being in some measure superseded 

 by artificial means. This apparatus then, this mechanism, these parts 

 accessory, we understand and explain, but we do not at all understand the 

 manner in which the light, when concentrated, acts on the retina, any 

 more than we do how the odoriferous particles act upon the nerve of olfac- 

 tion, and the parts, the use of which we comprehend, are no more than 

 parts of the organ which might have been extraneous. It is not therefore 

 that we have advanced further towards the complete understanding of the 

 mode in which any one sense more than another is impressed, but that we 

 have explained the uses of certain superadded parts in the one case, while 

 there are no superadded parts, or scarcely any, in the other. 



With the exception, then, of the conclusions respecting the mechanism 

 of the eye, and a very few points which have been established concerning 

 the ear, the facts observed with regard to the organs of the senses, have 

 not been made as yet subservient to anatomical or physiological science, 

 nor indeed to any conclusion save the general indication of design. 



Towards the classification of animals, the graud result of induction as 

 applied to Zoology, the consideration of the senses has contributed little 

 or nothing : the vital organs, those the uninterrupted action of which is 

 essential to life, have been taken as parts upon the complexity of which 

 the place of an animal in the great scale of animal existences is to depend, 

 and justly so. But it is found, that the development of the vital does not 

 imply a corresponding development in the sensorial functions ; so that the 

 class insects, with whose active habits and quick perceptions every one is 

 familiar, are actually inferior to the raollusca j or, in other words, the ant 

 and the bee, about whose — we might almost say moral— history volumes 

 have been written, are absolutely inferior in the development of their vital 

 organs to the oyster or slug. In truth the development of the organs of 

 the senses seems to have reference solely to the habits and circumstances 

 of the animal's life ; and although the adaptations consequent thereon are 

 extremely striking, they afford no just ground for a general classification. 



