IV. On the possibly dual origin of the mammalia

The recent discovery by Mr. Edward B. Poulton of non-functional teeth hidden beneath the bony plates of the jaws of the young Orni-thorhynchus is not only most interesting in itself, but taken in connexion with another recent discovery as to the anatomy of that animal, exceedingly suggestive. It is, of course, easy to assign too great a value to the forms of teeth, and everyone knows how Cuvier was thus led to associate the marsupial Carnivora with the placental Carnivores. There is an evident temptation also to exaggerate the significance of dental structure, both on account of the obvious nature of such characters and also because they are so exceptionally well preserved in fossil remains.