THE DESCENT OF THE PRIMATES 27 



tribute to the solution of certain questions of 

 primary importance concerning the relationship 

 of the three great subdivisions of the Mammalia 

 to each other and to the lower classes of Verte- 

 brate animals. It seems to me that the usual 

 way of looking upon these three subdivisions, 

 the Duckbills, the Marsupials, and the Placental 

 Mammals, as a real and historical sequence, in 

 which the first, having so many reptilian affini- 

 ities and standing lowest, gave rise in their turn 

 to Marsupials, which later on again became modi- 

 fied into Placentalia, is not in accordance with 

 their true relationship. 



I am in no way starting a new idea in lodging 

 a protest against the theory of the linear descent 

 of the Mammalian subgroups. Huxley was per- 

 haps the first to ventilate the same question. 

 Three years ago Osborn shook this traditional 

 arrangement to its foundations, by very cogent- 

 reasoning based on palaeontological research, in 

 his address, "On the Rise of the Mammalia in 

 North America." There was, as he expresses it, 

 " not a succession, but a unity of ancestry of the 

 Monotremes, Marsupials, and Placentals." Still, 

 the number of those who do not concur in this 

 conclusion is very considerable, and not likely to 

 be diminished for the next few years. Semon has 



