The group, which has also the alternative title of Didelphia, is by some authorities regarded as a sub-class of the mammalia of equal rank with the Monotremata, while by others it is brigaded with the placentals, so that the two together form a sub-class of equal grade with the one represented by the monotremes.
Thomas, Catalogue of Monotremata and Marsupialia in the British Museum (1888); "On Caenolestes, a Survivor of the Epanorthidae," Proc. Zool.
There are two orders, the Marsupialia and the Monotremata, which do not possess this organ; both these are found in Australia, to which region indeed they are not absolutely confined.
We pass on to the other curious order of non-placental mammals, that of the Monotremata, so called from the structure of their organs of evacuation with a single orifice, as in birds.
Latreille 6 published a new classification of the Vertebrata, which are primarily divided into Haematherma, containing the three classes of Maminifera, Monotremata and A y es; and Haemacryma, also containing three classes - Reptilia, Amphibia and Pisces.
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