EMfcRYOGENlC METHOD 53 



epoch belong either to the Monotremata or to the 

 Marsupials. 



These various hypotheses of Haeckel on the rela- 

 tions of these two large groups of mammals are far 

 from being certain palseontologically ; it is in no 

 way demonstrated that any of the Triassic Mammals 

 possessed a monotrematic organization and the 

 oldest authentic mammal known, the Dromaiherium 

 sylvestre of the Trias of Carolina, seems on the con- 

 trary to approach more nearly to the Marsupials. It 

 is therefore far below the Trias that we must look 

 for the quite hypothetical monotrematic ancestors 

 of this last group. 



As to the higher Placental Mammals, that is, 

 mammals with a complete mtra-uterine develop- 

 ment, Haeckel assumes them to be derived through 

 one or two branches detached from the stem 

 of the Marsupials at the commencement of 

 Tertiary times. But the Jena professor is him- 

 self obliged to acknowledge that palaeontological 

 proofs are lacking for the solution of this difficult 

 question. He therefore examines separately the 

 evolution of the two great groups of Placentals. 



1. The Ungulates with diffused placentas, which 

 are retained an important ancestral group of ani- 

 mals with manifold branches, from which in later 

 times were detached, through a special adaptation 

 to the environment, the Cetacea and the Edentata. 

 Haeckel recognizes perfectly the fundamental divi- 

 sion of the primitive Ungulates into those with an 

 odd number of toes or Imparidigitatce and Ungulates 

 with an even number or Paridigitatce ; but it 

 may be said generally, all attempts to construct 



