MAMMALIA 
The Mammalia constitute the highest and most important class of 
Vertebrata. They interest us more than the other classes, because 
they furnish us with those animals which are most useful in 
supplying us with food, in aiding us in our labours, and in 
providing us with the raw material required for so many of our 
manufactures. A land-inhabiting animal of this class is recog- 
nised at the first glance ; for its external and characteristic marks 
are numerous. The subordinate marine group of Cetacea, however, 
supplies rather a marked exception, consequent upon its adapta- 
tion to exclusively aquatic habits. 
Among the Yertebrata, these animals alone have, as their name 
imports ( mammon ), teats, which are situated either on the breast, 
or on the belly, or on both, and by means of which they suckle 
their young. The number of teats, in general, corresponds with 
the number of young of which each litter is composed. 
The majority of the Mammalia are covered with hair. Some, 
however, have smooth skins : as, for instance, the Whale and 
Porpoise-; others, as the Pangolins (. Manis ), are clad with dermal 
scales, which are altogether unlike those of Pep tiles or Fishes. 
The size of the Mammalia varies extremely : the scale extend- 
ing from the Whale and the Elephant to the Mouse, and to the 
most diminutive of Shrews, which are considerably less than half 
the size of the very smallest of the Mouse genus. 
Although less brilliant than the feathers of Birds and the scales 
of Fishes, the coats of the Mammalia offer to the eye very agreeable 
shades of colour. But nothing varies more than the peculiar 
nature of this coat. It is enough for us to remember, as a type of 
these differences, the hair of Fallow Deer, the bristles of the wild 
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