The anatomical differences by which the platypus, and its only allies the echidnas, are separated from all other mammals, so as to form a distinct sub-class, are described in the article Monotremata, where also will be found the main distinctive characters of the two existing representatives of the group. It is there stated that the early stages of the development of the young are not yet fully known. [Please select]
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There are several species of this great spine-bearing family; and many of them, especially the true porcupines and the echidnas, have burrows in the ground and thus have a double means of protecting themselves. [Please select]
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