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The Contemporary Review, Volume 36, September 1879

And comprises all opossums Didelphys

The whole of the orders of mammals yet mentioned agree in certain important details with respect to their reproductive processes, as well as in certain smaller anatomical peculiarities, and the whole of the creatures included within these orders are (and will be) often spoken of as _Placental Mammals_.

The only beasts which it yet remains to speak of are grouped in two other orders.

The first of these is called the order _Marsupialia_, and comprises all opossums (_Didelphys_), kangaroos (_Macropus_), phalangers (_Phalangista_), the Tasmanian wolf (_Thylacinus_), the dasyures (_Dasyurus_), the bandicoots (_Perameles_), and their allies. With the exception of the true opossums (_Didelphys_), all the members of the order are found in Australia or its vicinity, and nowhere else in the present day; although, as we shall better see hereafter, Europe once possessed animals closely allied to Australian forms of to-day--notably to a pretty little quadruped which bears the generic name _Myrmecobius_.

As last of the class of beasts, we have two extremely exceptional mammals (both found only in the Australian region), the duck-billed platypus (_Ornithorhynchus_), and the _Echidna_. The first of these, as its name implies, has a muzzle quite like the bill of a duck, with a squat, hairy body, and short limbs. The echidna is covered with strong, dense spines, and has a long and slender snout. These creatures together form the order _Monotremata_--an order which differs very much more from any other Mammalian order than any of the other orders of mammals differ one from another.

Thus, that great group which embraces man and beasts, and which group ranks as a "class"--the _class_ Mammalia--comprises (as we have now seen) a number of subordinate groups termed "orders," the orders being made up of families, and these again of genera.

It would be impossible as yet (when hardly any anatomical facts have been even referred to) to give the characters of the class _Mammalia_. It must at present suffice to point out that, in addition to mammary glands, the creatures have hot blood, and the body bears more or less hair--at least at some time of life.

We may now pass to the next class, that of birds--the class _Aves_. In spite of the great multitude of kinds which ornithologists enumerate--upwards of ten thousand species--there is very much less diversity of form amongst birds than there is amongst beasts.

Starting in the present class as in the preceding one from the most familiar kinds, we may begin with the domestic fowl. This is one of an "order" to which belong the peacock, all pheasants and tragopans (three forms which have their home in Central and Southern Asia), also the Guinea fowls (African forms), and the turkeys and curassows, which are American representatives of the order. Besides these may be mentioned partridges, grouse, black-cock, the capercalzie and quails, and, lastly, the megapodius or bush-turkey of Australia. This last is the only bird which hatches its eggs by artificial heat, depositing them in a mound of earth and decaying vegetable matter, wherein they are hatched fully-fledged, so that they can fly away immediately on leaving the egg. All the birds yet mentioned are called gallinaceous birds, or _Gallinae_, and sometimes _Rasores_ or "Scratchers."

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