yEOGENITORS OF MAN. 29 1 



Marsupials, both as regards their anatomy and their 

 ontogeny and phylogeny, form the direct transition from the 

 Monotrema to Placental animals (p. 247). Consequently, 

 human ancestors must also have existed among Marsupials. 

 They originated out of the Monotrema — which include 

 the primary Mammalia, or Promammalia — ^by the division of 

 the cloaca into the rectum and the urogenital sinus, by the 

 formation of a nipple on the mammary gland, and by the 

 partial suppression of the clavicles. The oldest Marsupials 

 at all events existed as early as the Jura period (perhaps 

 even in the Trias), during the Chalk period they passed 

 through a series of stages preparing the way for the origin 

 of Placentalia. The certain proof of our derivation from 

 Marsupials — nearly akin to the still living opossum and 

 kangaroo in their essential inner structure — is furnished 

 by the comparative anatomy and the ontogeny of 

 Mammalia. 



Eighteenth Stage : Semi-apes (Prosimise). 



The small group of Semi-apes, as we have already seen, 

 is one of the most important and most interesting orders of 

 Mammalia. It contains the direct primary forms of Genuine 

 Apes, and thus also of Man. Our Semi-ape ancestors probably 

 possessed only a very faint external resemblance to the still 

 living, short-footed Semi-apes (Brachytarsi), especially the 

 Maki, Indri, and Lori (p. 256). They originated (probably 

 at the beginning of the Cenolithic, or Tertiary period) out 

 of Marsupials of Rat-like appearance by the formation of a 

 placenta, the loss of the marsupium and the marsupial 

 bones, and by the higher development of the commis- 

 sures of the braia The certain proof that Genuine Apes, 



