There are in Australia numerous Mammalia, occupying the same relation and answering the same purposes as the Mammalia of other countries.  Some of them are domesticated by the natives, and serve them with meat, milk, wool, as our domesticated animals serve us.  Representatives of almost all types, Wolves, Foxes, Sloths, Bears, Weasels, Martens, Squirrels, Rats, etc., are found there; and yet, though all these animals resemble ours so closely that the English settlers have called many of them by the same names, there are no genuine Wolves, Foxes, Sloths, Bears, Weasels, Martens, Squirrels, or Rats in Australia.  The Australian Mammalia are peculiar to the region where they are found, and are all linked together by two remarkable structural features which distinguish them from all other Mammalia and unite them under one head as the so-called Marsupials.  They bring forth their young in an imperfect condition, and transfer them to a pouch, where they remain attached to the teats of the mother till their development is as far advanced as that of other Mammalia at the time of their birth; and they are further characterized by an absence of that combination of transverse fibres forming the large bridge which unites the two hemispheres of the brain in all the other members of their class.  Here, then, is a series of animals parallel with ours, separated from them by anatomical features, but so united with them by form and external features that many among them have been at first associated together.

This is what Cuvier has called subordination of characters, distinguishing between characters that control the organization and those that are not essentially connected with it.  The skill of the naturalist consists in detecting the difference between the two, so that he may not take the more superficial features as the basis of his classification, instead of those important ones which, though often less easily recognized, are more deeply rooted in the organization.  It is a difference of the same nature as that between affinity and analogy, to which I have alluded before, when speaking of the ingrafting of certain features of one type upon animals of another type, thus producing a superficial resemblance, not truly characteristic.  In the Reptiles, for instance, there are two groups,—­those devoid of scales, with naked skin, laying numerous eggs, but hatching their young in an imperfect state, and the Scaly Reptiles, which lay comparatively few eggs, but whose young, when hatched, are completely developed, and undergo no subsequent metamorphosis.  Yet, notwithstanding this difference in essential features of structure, and in the mode of reproduction and development, there is such an external resemblance between certain animals belonging to the two groups that they were associated together even by so eminent a naturalist as Linnaeus.  Compare, for instance, the Serpents among the Scaly Reptiles with the Caecilians among the Naked Reptiles.  They have the same