o these two groups.[2] The
evidence furnished by oology and the newly-hatched young seems to favour
Brandt's views. The abortion of the _rectrices_ in the gerbes, while
these feathers are fairly developed in the divers, is another point that
helps to separate the two Families.

The commonest species of _Colymbus_ is _C. septentrionalis_, known as
the red-throated diver from an elongated patch of dark bay which
distinguishes the throat of the adult in summer dress. Immature birds
want the bay patch, and have the back so much more spotted that they are
commonly known as "speckled divers." Next in size is the black-throated
diver, _C. arcticus_, having a light grey head and a gular patch of
purplish-black, above which is a semicollar of white striped vertically
with black. Still bigger is the great northern diver, _C. glacialis_ or
_torquatus_, with a glossy black head and neck, two semicollars of white
and black vertical stripes, and nearly the whole of the black back and
upper surface of the wings beautifully marked with white spots, varying
in size and arranged in belts.[3] Closely resembling this bird, so as to
be most easily distinguished from it by its yellow bill, is _C. adamsi_.
The divers live chiefly on fish, and are of eminently marine habit,
though invariably resorting for the purpose of breeding to freshwater
lakes, where they lay two dark brown eggs on the very brink; but they
are not unfrequently found far from the sea, being either driven inland
by stress of weather, or exhausted in their migrations. Like most birds
of their build, they chiefly trust to swimming, whether submerged or on
the surface, as a means of progress, but once on the wing their flight
is strong and they can mount to a great height. In winter their range is
too extensive and varied to be here defined, though it is believed never
to pass, and in few directions to approach, the northern tropic; but the
geographical distribution of the several forms in summer requires
mention. While _C. septentrionalis_ inhabits the north temperate zone of
both hemispheres, _C. arcticus_ breeds in suitable places from the
Hebrides to Scandinavia, and across the Russian empire, it would seem,
to Japan, reappearing in the north-west of North America,[4] though its
eastern limit on that continent cannot be definitely laid down; but it
is not found in Greenland, Iceland, Shetland or Orkney. _C. glacialis_,
on the contrary, breeds throughout the north-eastern pa