COLOURS OF MAMMALS 
hibérnates. They do not remain for hours in a motion- 
less condition save when asleep. 
So far as external characters are concerned the above 
observations embody the principal points in which 
the group differs from those of vertebrates lying lower 
in the series. There are, however, still remaining, a few 
characters which are highly noteworthy among the 
mammalia without being absolutely diagnostic. It 
will be readily observed in reviewing the large series of 
mammals at the Zoo, and comparing them with the 
larger series of birds, that the mammalia for the most 
part are clad inasober livery. There is nowhere in the 
group that development of brilliant primary colours 
such as we see so very commonly among birds. There 
are no reds, greens and blues, the utmost brilliancy of 
hue being bright browns contrasting with white, and 
a few brighter colours, not of hair, but of naked skin, 
such as the muzzle and ischial callosities of some monkeys. 
If may be that correlated with this absence of striking 
coloration is the predominance of the senses of smell 
and hearing over sight. It is broadly true of the 
mammalia, that they smell and hear rather than see. 
While of birds it is equally true to say, that they see 
rather than smell. That this point of view is in the 
main correct is shown by another very characteristic 
feature of the mammalia. In various parts of the body 
glands open on to the surface; these glands produce 
variously smelling secretions, of which musk, civet, and 
castoreum, are examples. The odoriferousness of the 
houses in which the mammalia are confined is an un- 
mistakable proof of this ; and the fact that birds are 
at least by no means so strongly smelling convinces 
us of the absence of glands in the skins of those animals. 
The same may be said of reptiles and amphibia, broadly 
considered—for here as elsewhere there are exceptions. 
There are for example musky smelling glands among 
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