AND THEIR FUNCTIONS. 185 



ments in the medium, e.g., air or water, which acted on 

 the eye by the agency of the Diaphanous.* He beheved 

 that the eye was of ivater, a proof being that water ran 

 from it, when ruptured, but he did not beheve that the eye 

 was capable of sight because of this presence of water, 

 except in so far as it was transparent. In this respect, air 

 would have been as efficient, but Aristotle believed that the 

 eye was of ivater because this is less yielding, and is also 

 more easily confined than air.t 



Aristotle knew very little of the anatomy of the eye, 

 beyond certain parts which were evident on cursory ex- 

 amination, viz., the pupil, the iris, the white sclerotic, the 

 aqueous or the vitreous humour, or both, and the nictitating 

 membrane of some animals. 



All viviparous animals, he says, except the Aspalax 

 (mole), have eyes, for the Aspalax does not see at all, nor 

 does it possess eyes which are plainly visible, but, when the 

 skin is removed, the places for the eyes are seen, and the 

 " irises " occupy the exact positions naturally belonging to 

 the eyes, as seen from outside, the appearance being just as 

 if the eyes had been injured during their development, and 

 the skin had grown over them.t 



In many other passages Aristotle refers to the blindness 

 of the Aspalax. This was probably the common mole 

 {Talpa europea), but some have tried to identify it with the 

 so-called blind mole (T. cccca), which Dobson describes as a 

 distinct species, characterized chiefly by the presence of 

 membranes over its eyes,§ while Camerano considers it to 

 be merely a variety of the common mole. |1 



Whichever view is correct, it is certain that skins of the 

 so-called blind moles are not readily distinguishable from 

 those of the common moles, and Mr. Oldfield Thomas has 

 assured me that not all blind moles have membranes over 

 their eyes. 



When Aristotle refers to the covering of the eyes of 

 Aspalax, he uses the word derma, which refers particularly 

 to the skin of the body, and, inH. A. iv. c. 8, s. 2, he calls 

 it the thick skin enveloping the animal's head. There is no 

 suggestion that he refers to membranes covering the eyes. 



-•' De Anima, ii. c. 7, 419a ; De Sensu, dc, c. 3, 440a. 

 f De Sensu, dc, c. 2, 438a. J H. A. i. c. 8, s. 3. 



§ Monogr. of the Insectivora, Part 2, 1883, p. 139. 

 II Meyn. della Eeale Accad. delle Sci, di Torino, 2nd series, vol. 37, 

 1886, pp. 445, 446. 



