go together to
constitute the order called _Steganopodes_. The flamingoes are isolated,
and by themselves form the order _Odontoglossae_. The same is the case
with the penguins, which have the order _Impennes_ assigned exclusively
to them.

The ducks and geese form alone the order _Lamellirostres_, in which is
included the curious bird _Palamedea_, which is a goose adapted to live
in trees in harmony with its South American forest habitat.

The rails and coots go with the bustards and cranes to constitute the
order _Alectorides_. Similarly the auks, divers, puffins, terns, and
grebes, noddies, and guillemots may be associated together in one
order--the order _Pygopodes_. The gulls and petrels form another
association--the order _Gaviae_; while the plovers, snipes, curlews,
peewits, turnstones, &c., constitute the order _Limicolae_. The order
_Heridiones_ includes the herons, the bitterns, the storks, spoonbill,
ibis, &c.

All the foregoing birds have a multitude of points in common; indeed, so
close is the similarity of their structure that their subdivision into
orders is a matter of much difficulty and dispute. They are collectively
spoken of as the _Carinatae_, from the keeled form of their breast-bone.

Widely apart from them stands another group made up almost entirely of
large birds, which agree not only in having no power of flight, but also
in certain significant structural characters, amongst which may be
mentioned the absence of a keel on the breast-bone.

This latter group is sometimes spoken of as the order _Struthiones_ from
the ostrich (_Struthio_), which is its typical form. Sometimes these
keelless birds are called _Ratitae_. Besides the ostrich, the rhea,
cassowary, and emeu are included within the group; also the small and
nocturnal _Apteryx_ of New Zealand and those giants of featherdom, the
huge species of dinornis, all also of New Zealand and all now extinct.

With this our list of birds might close, but for a bird which anciently
existed in Europe so strangely different from all modern kinds, that it
must certainly be here adverted to. This bird is the _Archeopteryx_,
found in fossil in the Solenhofen States.

The class Aves, like the class Mammalia, consists of animals with hot
blood, but all birds have feathers and a number of other peculiarities
of structure, as will appear later.

The next class to be adverted to is the class which includes all
reptiles properly so-called--the class _