ngs and tail, and very dense plumage. They frequent, exclusively,
mountain torrents in the northern hemisphere, and obtain their food
entirely in the water, consisting, as it does, of water-beetles,
caddis-worms, and other insect-larvae, as well as numerous small
fresh-water shells. These birds, although not far removed in structure
from thrushes and wrens, have the extraordinary power of flying under
water; for such, according to the best observers, is their process of
diving in search of their prey; their dense and somewhat fibrous
plumage retaining so much air that the water is prevented from touching
their bodies or even from wetting their feathers to any great extent.
Their powerful feet and long curved claws enable them to hold on to
stones at the bottom, and thus to retain their position while picking
up insects, shells, etc. As they frequent chiefly the most rapid and
boisterous torrents, among rocks, waterfalls, and huge boulders, the
water is never frozen over, and they are thus able to live during the
severest winters. Only a very few species of dipper are known, all those
of the old world being so closely allied to our British bird that some
ornithologists consider them to be merely local races of one species;
while in North America and the northern Andes there are two other
species.

"Here, then, we have a bird, which, in its whole structure, shows a
close affinity to the smaller typical perching birds, but which has
departed from all its allies in its habits and mode of life, and has
secured for itself a place in Nature where it has few competitors and
few enemies. We may well suppose,* [[*Note characteristic phrase "We may
suppose that,--." G.]] that, at some remote period, a bird which was
perhaps the common and more generalized ancestor of our thrushes,
warblers, wrens, etc., had spread widely over the great northern
continent, and had given rise to numerous varieties adapted to special
conditions of life. Among these some took to feeding on the borders of
clear streams, picking out such larvae and mollusks as they could reach
in shallow water. When food becomes scarce they would attempt to pick
them out of deeper and deeper water, and while doing this in cold
weather many would become frozen and starved. But any which possessed
denser and more hairy plumage than usual, which was able to keep out the
water, would survive; and thus a race would be formed which would depend
more and more on this kind of f