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Show 1882.] PROF. W. H. FLOWER ON THE EDENTATA. 359 Cuvier's order included the Ornithorhynchus and Echidna, animals of which the structure was then imperfectly known, but which are now by almost universal consent removed to an altogether different section of the class. Otherwise its limits are those now adopted. The name Edentata, moreover, is now so generally used, and its meaning so well understood as a conventional term, that it would be very undesirable to substitute any other for it. In fact similar reasons might be given for ceasing to use nearly all the current ordinal designations of mammals. It might be equally well objected that all the Carnivora are not flesh-eaters, many of the Marsupialia have not pouches, and so forth. The few common characters by which the Edentata are associated are too well known to need repetition. The principal one is the absence of any trace of the typical heterodont and diphyodont dentition, found in a more or less modified form in all other placental mammals \ The one genus Tatusia presents a startling exception, in the presence of a set of milk-teeth, with (according to Burmeister) distinct roots implanted in separate alveoli, and (according toC. Tomes) distinct enamel-organs, if not enamel. This is one of the most important facts bearing upon the evolution of the Edentates yet discovered, though its full signification is not yet evident. It is highly probable that most, if not all, of the existing Edentates are the very much differentiated representatives of a large group, the greater number of which are now extinct, and which have become so without ever attaining a high grade of organization. The great diversity of structure, the high degree of specialization to which many have attained, the paucity of species and even of individuals, their limited area of distribution, and their small size compared with known extinct forms, all show that they belong to an ancient and waning race, the members of which still hold their own either by the remoteness and seclusion of their dwelling-places, their remarkable adaptation of structure to special conditions of life, or by aid of the peculiar defensive armature with which they are invested. Their former history can, however, only be surmised, rather than read, at present; for though we have ample evidence of the abundance and superior magnitude of certain forms in the most recent and post-Tertiary geological age, aud in one part of the world, beyond that time (i. e. in the true Tertiary period), and in other parts of the world than America, their fossil remains hitherto discovered are only fragmentary, giving a most imperfect idea of their actual condition, as well as affording no indications that serve to connect them with certainty to any other branch of the class. The existing Edentates readily group themselves into five distinct families, of the limits of which there is no reasonable doubt. These a r e . i# The B R A D Y P O D I D ^ E , containing two genera, Bradypus and Cholozpus. 2. TheMYRMECOPHAGiD^E, containing three distinct modifications, worthy of generic rank-Myrmecophaga, Tamandua, and 1 The Cetacea are possible exceptions; but embryological and paloeontological researches appear to show that their dentition may be derived from the ordinary mammalian type. |
