SHREWS, MOLES, etc.,— Order, INSECTIVORA 
THE next order of mammals to be considered is that of the 
Insectivora, —a collection difficult to define, of small-sized 
and plantigrade, but otherwise very unlike animals, which feed 
almost wholly on insects or worms. They are found in all 
parts of the world except Australia and South America, but near 
relatives are sometimes widely separated, the insectivores of 
the West Indies, for example, being closely allied to those of 
Madagascar. Some are subterranean, others aquatic or ar- 
boreal. Deep-seated distinctions in structure correspond to 
these variations in mode of living, and strengthen the evidence 
from fossils that this group represents ‘‘little altered survivors 
of some of the most primitive placental mammals.” 
There is a good deal of evidence, direct and indirect, that the insecti- 
vores were once a far more abundant and important group. So far as we 
can tell from the rare and fragmentary jaws and tiny teeth, the order is of 
immense antiquity, being traceable far back into the Age of Reptiles, during 
the Jurassic period. At all events, they were a numerous and varied group 
in the Eocene, including arboreal, terrestrial, and aquatic types, some of 
considerable size, and several species very abundant, besides many minute 
forms comparable to the moles and shrews of the present day, and very 
likely ancestral to them. At the beginning of the Tertiary, they are indis- 
tinguishable from the earlier of the creodonts, but the latter soon branched 
off, becoming adapted to a predaceous life, while the insectivores retained 
more nearly their ancient mode of living and failed to keep progress with 
the higher groups, so that in the later Tertiary epochs they diminished rapidly 
in numbers and variety. To-day only a few survivors are left, protected 
from their enemies by some unusual defense, as in the case of the hedge- 
hogs; by a subterranean mode of life, as the moles; by their agility, minute 
size, and unpleasant odor and taste, as are the shrews; or, finally, by their 
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