It is the more remarkable because we find a somewhat
similar structure in the molar teeth of the elephants, which, like the
rodents, have the incisor teeth largely developed and widely separated
from the molars.
There is nothing in the appearance of the water-rat which gives any
indication of its aquatic habits.
For example, we naturally expect to find that the feet of swimming
animals are webbed. The water-loving capybara of South America, the
largest existing rodent, has its hoof-like toes partially united by
webs, so that its aquatic habits might easily be inferred even by those
who were unacquainted with the animal. Even the otter, which propels
itself through the water mostly by means of its long and powerful tail,
has the feet furnished with webs. So has the aquatic Yapock opossum of
Australia, while the feet of the duck-bill are even more boldly webbed
than those of the bird from which it takes its popular name. The
water-shrews (whom we shall presently meet) are furnished with a fringe
of stiff hair round the toes which answers the same purpose as the web.
But the structure of the water-rat gives no indication of its habits, so
that no one who was unacquainted with the animal would even suspect its
swimming and diving powers.
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