94 Bulletin American Museum of Natural History. [Vol. XXVII, 



HUXLEY, 1880. 



'On the Application of the Laws of Evolution to the Arrangement of the 

 Vertebrata, and more particularly, of the Mam,malia.' Proc. Zool. 



Soc, 1880, pp. 649-662. 



One of the most important features of this memorable analysis, the general 

 bearings of which have been noted above, is the fact that the main divisions 

 are not founded upon the traditional criteria, such as the number of teeth 

 or of digits, but upon deep-seated anatomical characters having little imme- 

 diate relations to particular life habits. This method had been initiated by 

 de Blainville, and especially dwelt upon by Gill (see above, p. 91), and the 

 modern development of embryology and comparative anatomy enabled 

 Huxley to apply to the problem of mammalian classification such recondite 

 criteria as the condition of the malleus and the relations of the ureteric 

 apertures. The terms "HAiwtheria," "Prototheria," "Metatheria," ''Eu- 

 theria," being intended to describe stages of evolution were employed 

 in a somewhat different sense from that of the purely systematic terms 

 "Prototheria" and "Eutheria," which had been used first by Gill in 1872 

 (p. 92). The arrangement of the diagram seems to imply that all the orders 

 of Eutheria were derived independently from remote Hypotherian stocks — 

 an extreme form of the "polyj^hyletic origin" idea. The Primates (Anthro- 

 poidea) and Lemuroids seem to be conceived as independent lines both 

 related remotely to the INIarsupialia. The Rodents are placed between the 

 Lemuroids and the Proboscidea while the Sirenia are between the Pro- 

 boscidea and the Ungulata (Perissodactyla + Artiodactyla). The Hyra- 

 coidea are placed between the Ungulata and the Insectivora, while the 

 Cetacea lie between the latter group and the Carnivora; the Cheiroptera 

 follow; the Edentata, perhaps regarded as the lowest of the Eutheria 

 are next to the Monotremata, an association regarded as valid by many of 

 Huxley's predecessors. 



