AN INVISIBLE MONKEY 169 
With regard to the great panda, we have at present no 
information. It may be suggested, however, that the start- 
ling contrast presented by its streaks and patches of creamy 
white on a jet-black ground may harmonise with patches 
of snow on black rocks, or possibly with the lines of light 
‘between the dark stems of forest trees. 
Be this as it may, Dr. Gregory’s observations have solved 
the problem of the use of the remarkable coloration of 
the guerezas, which has so long puzzled naturalists. Like 
others of their kind, these monkeys pass most of their 
time high up on trees, where they sleep either resting on 
a bough or hanging beneath by their hands, or hands and 
feet. Now, in the dense forests clothing Mount Kilima 
Njaro and other districts of East Africa, the black-barked 
boughs are thickly draped with pendent masses and wreaths 
of grey beard-moss or lichen, which reach for several feet 
below them. ‘As the monkeys hang from the branches,” 
writes Dr. Gregory, “they so closely resemble the lichen 
that I found it impossible to recognise them when but a 
short distance away.” 
We have thus decisive evidence that the black and 
white coloration of the guerezas protects these animals 
by a close resemblance to their inanimate surroundings. 
There are, however, certain smaller mammals with a 
similar type of coloration in which the startling contrast 
of black and white seems to be for the purpose of rendering 
them conspicuous; and as some at least of these creatures 
are endowed with a most disgusting odour, their con- 
spicuousness has been regarded as warning other animals 
from attacking them. The best known of these creatures 
are the ill-famed American skunks, which are in the habit 
of stalking over the Argentine Pampas in full daylight, 
with the most consummate indifference to the presence of 
