GENERATION OF ANIMALS, V. i. 



in practice a multiplicity of colour ; some are blue, 

 some greyish-blue, some dark, some yellow. Hence 

 in the case of the other animals, just as the individuals 

 of anv class do not differ from each other, so they do 

 not differ from themselves," the reason in both cases 

 being that they are not naturally constituted to have 

 more than one colour. The greatest multiplicity of 

 colour, however, among the other animals is found in 

 the horse ; indeed in some horses the two eyes are 

 of odd colours.^ Xo other animal is noticeably 

 affected in this way, though some human beings are. 



Well, then, for the fact that in the other animals, 

 young or old, no noticeable change occurs, whereas 

 in infants a change does occur, we must consider 

 simply this to be a sufficient cause, viz., that in 

 animals this part is single-coloured, in human beings 

 multicoloured ; while for the fact that the young 

 have bluish eyes and not some other colour, the 

 reason is that their parts are weaker than those of 

 adults, and blueness is a form of weakness. 



We must now determine the general question of 

 why eyes differ, and what is the cause why some are 

 blue, some greyish-blue, some yellow, some dark. 

 There is a theory, stated by Empedocles, that blue 

 eyes are fiery in composition, while dark ones contain 

 more water than fire, and that therefore blue eyes 

 are not keen-sighted in the daytime owing to their 

 deficiencv of water, and the other ones suffer in the 

 same way at night owing to their deficiency of fire. 

 But if we ought in point of fact "^ to posit that the 

 sight,** in all cases, consists of water, not of fire, then 



' This is Aristotle's own theory ; see De anima 425 a 4 ; 

 De aensu 438 a 5, 13 if., b 5. For details, see App. B § 28. 

 ** i.e., the organ of sight, as often in this discussion. 



495 



