GENERATION OF ANIMALS, V. v.-vi. 



the skin in the various instances, whereas the skin 

 does not change at all in accordance with the winds 

 and the sun. 



Of the animals, some are single-coloured (by VI 

 which I mean that the whole class has a single colour Coionr- 



1 • • 1 1 • changes 



only, e.g., all lions are tawny ; and a similar thing 

 obtains in the case of birds, fish, and the other 

 animals) ; others are many-coloured, yet at the same 

 time whole-coloured (by which I mean that the whole 

 body is of the same colour, e.g., an ox is white all 

 over, or dark all over) ; others still are variegated. 

 " \'ariegated " has two meanings : (a) as referred to 

 a class of animals — like the leopard, and peacock, and 

 certain fishes, for instance the tkratta,'^ as it is called ; 

 (b) sometimes the class as a whole is not variegated, 

 but variegated individuals are found : examples are, 

 oxen and goats, and certain birds, e.g., pigeons, and 

 there are other classes of birds where this same 

 condition is found. Change of colour is much com- 

 moner among the whole-coloured animals than among 

 the single-coloured, both {a) the reciprocal change 

 between the individual colours (found in the class), 

 i.e., one simple colour changes into another, e.g., white 

 animals produce black ones and black ones white ; and 

 also (6) the change which results in a mixture of the 

 two. The reason for this is that it is a natural attri- 

 bute of the whole class not to have one single colour : 

 the class is mobile in both directions, and so provides 

 more examples of interchange of colours and also of 

 variegation. The single-coloured animals behave in 

 the opposite way to this : they do not change, unless 

 owing to some affection, and then but rarely ; thus, 

 cases have been observed of a white partridge, ** raven, 

 sparrow, and bear. These results occur M'hen the 



537 



