ORDER I. _Cursores._ Running birds with no keeled breastbone. Examples:
ostrich, cassowary.
ORDER II. _Passeres._ Perching birds; three toes in front, one behind. Over
one half of all species of birds are included in this order. Examples:
sparrow, thrush, swallow.
ORDER III. _Gallinae._ Strong legs; feet adapted to scratching. Beak stout.
Examples: jungle fowl, grouse, quail, domestic fowl.
ORDER IV. _Raptores._ Birds of prey. Hooked beak. Strong claws. Examples:
eagle, hawk, owl.
ORDER V. _Grallatores._ Waders. Long neck, beak, and legs. Examples: snipe,
crane, heron.
ORDER VI. _Natatores._ Divers and swimmers. Legs short, toes webbed.
Examples: gull, duck, albatross.
ORDER VII. _Columbinae._ Like Gallinae, but with weaker legs. Examples: dove,
pigeon.
ORDER VIII. _Pici._ Woodpeckers. Two toes point forward, two backward, and
adaptation for climbing. Long, strong bill.
ORDER IX. _Psittaci._ Parrots, hooked beak and fleshy tongue.
ORDER X. _Coccyges._ Climbing birds, with powerful beak. Examples:
kingfisher, toucan, and cuckoo.
ORDER XI. _Macrochires._ Birds having long-pointed wings, without scales on
metatarsus. Examples: swift, humming bird, and goatsucker.
Mammals.--Dogs and cats, sheep and pigs, horses and cows, all of our
domestic animals (and man himself) have characters of structure which cause
them to be classed as mammals. They, like some other vertebrates, have
lungs and warm blood. They also have a hairy covering and bear young
developed to a form similar to their own,[28] and nurse them with milk
secreted by glands known as the _mammary glands_; hence the term "mammal."
Footnote 28: With the exception of the monotremes.
[Illustration: The bison, an almost extinct mammal.]
Adaptations in Mammalia.--Of the thirty-five hundred species, most inhabit
continents; a few species are found on different islands, and some, as the
whale, inhabit the ocean. They vary in size from the whale and the elephant
to tiny shrew mice and moles. Adaptations to different habitat and methods
of life abound; the seal and whale have the limbs modified into flippers,
the sloth and squirrel have limbs peculiarly adapted to climbing, while the
bats have the fore limbs modeled for flight.
Lowest Mammals.--The lowest are the monotremes, animals which lay eggs like
the birds, although they are provided with hairy covering like other
mammals. Such are the Australian spiny anteater and the duck mole.
All other mammals bring forth their young developed to a form similar to
their own. The kangaroo and opossum, however, are provided with a pouch on
the under side of the body in which the very immature, blind, and helpless
young are nourished until they are able to care for themselves. These
pouched animals are called _marsupials_.