Before proceeding to notice an amendment which has been proposed in regard to the homology of the one successional tooth of the marsupials, certain other features connected with it and its predecessor discussed by Flower may be briefly mentioned. He noticed, to quote from an admirable epitome of his observations on this point, drawn up by Professor M’Intosh in the _Scottish Review_ for 1900, “that there were considerable differences in the various genera as to the relative period of the animal’s life at which the fall of the temporary molar and the evolution of its successor takes place. In some, as in the rat-kangaroos, it is one of the latest, the temporary tooth retaining its place and its functions until the animal has nearly, if not quite, reached its full growth, and is not shed until all the other teeth are in position and use. On the other hand, in the Tasmanian wolf the temporary tooth is very rudimentary in size and form, and is shed or absorbed before any other teeth enter the gum. Anterior to the period of Sir William Flower’s communication, mammals had been, in regard to the succession of their teeth, divided into two groups—the Monophyodonts, or those that generate a single series of teeth, and the Diphyodonts, or those that develop two sets of teeth, but, as he pointed out, even in the most typical Diphyodonts the successional process does not extend to the whole of the teeth, always stopping short of those situated most posteriorly in each series. The pouched animals (marsupials), he stated, occupied an intermediate position, presenting, as it were, a rudimentary diphyodont condition, the successional process being confined to a single tooth on each side of each jaw.” All this is unexceptionable. Flower, however, went further than this, and claimed that the true molar teeth of mammals correspond serially with the permanent premolars, canines, and incisors, and not with their deciduous predecessors. And he therefore urged (as indeed must be the case on these premisses) that the whole dentition of adult marsupials corresponds with the permanent dentition of placentals. A further inference from this is that the milk-teeth, instead of being an original development, may rather be a set superadded to meet the temporary needs of mammals whose permanent set is of a highly complex type.