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CHAPTEE V. 



THE SUBCLASSES AND ORDERS INTO WHICH THE CLASSES 

 OF THE VERTEBRATA ARE DIVISIBLE. 



I. THE MAMMALIA. 



A GREAT many systems of classification of the Mammalia have 

 been proposed, but, as any one may imagine from the nature of 

 the case, only those which have been published within the last 

 forty or fifty years, or since our knowledge of the anatomy of 

 these animals has approached completeness, have now any 

 scientific standing-ground. I do not propose to go into the 

 history of those older systems, which laboured more or less 

 under the disqualification of being based upon imperfect 

 knowledge, but I shall proceed, at once, to that important 

 step towards dividing the Mammalia into large groups, which 

 was taken by the eminent French anatomist, M. de Blainville, 

 so far back as the year 1816. M. de Blainville pointed out that 

 the Mammalia might be divided into three primary groups, 

 according to the character of their reproductive organs, especially 

 the reproductive organs of the female. He divided them into 

 " Ornithodelphes," " Didelphes," " Monodelphes ;" or, as we 

 might term them, ORNITHODELPHIA, DIDELPHIA, MONODELPHIA. 

 Now, I do not mean to assert that M. de Blainville defined these 

 different groups in a manner altogether satisfactory, or strictly 

 in accordance with all the subsequently discovered facts of 

 science, but his great knowledge and acute intuition led him to 

 perceive that the groups thus named were truly natural divisions 

 of the Mammalia. And the enlargement of our knowledge by 



