THE DESCENT OF THE PRIMATES 25 



lated, the balancing of the skull and brain on 

 the spinal column bemg thereby facilitated. 

 Many of the lower Primates thus realize con- 

 ditions highly favorable for the adoption of the 

 erect posture. Secondly, we should remember 

 that this erect posture is not even restricted to 

 the Primates, as we find among the Lemurs 

 the genus Propithecus which, when it has come 

 down from a tree, walks about on its hind legs, 

 even without resting its arms on the ground 

 as do the Gibbons. This important peculiarity 

 of Propithecus, figured by Milne-Edwards and 

 Grandidier in 1875, was already known to 

 Flaccourt not less than two hundred years ago. 

 To ascribe the same to the remotest Csenozoic, 

 or even to the Mesozoic, ancestors of man is 

 then not in itself irreconcilable with observa- 

 tion. As to the placental characteristics of this 

 hypothetical intermediate stage, I should think 

 that the considerable degree to which already now 

 the extremes (Erinaceus and Homo) resemble 

 each other in certain respects, justify us in accept- 

 ing them as here indicated. It would, neverthe- 

 less, be worth while to inquire if in any of the 

 living genera of American monkeys, a decidua 

 reflexa and a discoid placenta of Erinacean type 

 of development might also be shown to exist. 



