If a hair be cut, it does not grow at the point of section; but it
gets longer by growing upward from below. In fishes the scales grow
harder and thicker with age, and when the amimal gets emaciated or
is growing old the scales grow harder. In quadrupeds as they grow
old the hair in some and the wool in others gets deeper but scantier
in amount: and the hooves or claws get larger in size; and the same is
the case with the beaks of birds. The claws also increase in size,
as do also the nails.
12
With regard to winged animals, such as birds, no creature is
liable to change of colour by reason of age, excepting the crane.
The wings of this bird are ash-coloured at first, but as it grows
old the wings get black. Again, owing to special climatic
influences, as when unusual frost prevails, a change is sometimes
observed to take place in birds whose plumage is of one uniform
colour; thus, birds that have dusky or downright black plumage turn
white or grey, as the raven, the sparrow, and the swallow; but no case
has ever yet been known of a change of colour from white to black.
(Further, most birds change the colour of their plumage at different
seasons of the year, so much so that a man ignorant of their habits
might be mistaken as to their identity.
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