840 M. Hilaire o?i tJie Visimi of the Mole. 



Where, then, does this principle reside ? The author id- 

 tends, in a future memoir, to point out the parts in which his 

 experiments have led him to place it, and to shew the mode ac- 

 cording to which it is distributed in them. 



On the Vision of the Mole. By M. Geoffboy Saint 

 Hilaire. 



JJoES the mole see.^ Aristotle and all the Greek philosophers 

 believed it to be blind. Galen, on the contrary, maintained 

 that it sees, affirming that it is possessed of all the means of vi- 

 sion. The question has again been taken up in our days: 

 naturalists have discovered the eye of the animal. It is very 

 small, being at the most not larger than a grain of millet-seed ; 

 its colour is deep black ; it is hard to the touch, and is with 

 difficulty depressed by squeezing it between the fingers. Be- 

 sides the eyelid which covers it, it is defended by long hairs, 

 which, crossing each other, form a thick and close fillet. Such 

 an eye ought to be destined for seeing, but anatomists have 

 found no optic nerve in it. What could be the purpose of an 

 eye destitute of the nerve which, in the other animals, transmits 

 the visual sensations to the brain .'' This consideration natural- 

 ly leads back to the opinion of Aristotle and the Greeks, and 

 would induce us to think that the mole, although it has an eye, 

 does not see with it, and that, consequently, this eye is nothing 

 but a rudimentary point without use. 



Direct experiments, however, made at the request of M. 

 Geoffroy St Hilaire, demonstrate, in the most incontestible man- 

 ner, that the mole makes use of its eyes, since it turns aside to 

 avoid the obstacles that are placed in its way. But, if the mole 

 sees, how happens it to have no optic nerve .^ M. Serres 

 thought that the optic nerve was supplied by an upper twig of 

 the fifth pair, that which may be considered as analogous to the 

 ophthalmic branch of Willis. 



According to M. Geoffroy St Hilaire, the transference of 

 function to a nerve which is not naturally destined to perform 

 it, does not exist. The mole sees by means of a particular nerve ; 

 but this nerve not being able, on account of the too great ex- 



