THE LIFE OF MAMMALS 
toes. The former is the more specialized, widespread, and cele- 
brated. The two differ in their teeth and certain other ana- 
tomical points, and also in the particular tinge of green on the 
coarse, brittle hair. 
This greenness of the hair is not only singular as a mammalian color, 
but in its nature, for it is due to a growth of microscopic plants (alge), 
which become rooted in the crevices of the surface of the hair, and flourish 
there as long as the 
animal lives. The 
hairs of the two kinds 
of sloths differ in 
structure, and sup- 
port different species 
of alga; and the 
plant does not be- 
gin to grow in the fur 
of the young (from 
spores caught from its 
mother’s fur) until it 
approaches adulthood 
and goes away by it- 
self. This fact, and 
the broader one that 
it helps to make the 
animal less easily 
visible in the foliage, 
causes this growth of 
alge to be regarded 
as a protective adap- 
Copyright, n. ¥. Zodl. Suviety. Sanborn, Phot. tation. Attention was 
TARDO, OR TWO-TOED SLOTH. called to it long ago. 
Thus Van Sack -notes 
that “the color and even the shape of the hair are much in appear- 
ance like withered moss, and serve to hide the animal in the trees, but 
particularly when it gets that orange-colored spot between the shoulders, 
and lies close to the tree; it looks then exactly like a piece of branch 
where the rest has been broken off, by which the hunters are often de- 
ceived.” The color disappears from stuffed skins, because the minute 
vegetation dies after the animal itself ceases to live. 
474 
