2/3 THE DOCTRINE OF DESCENT. 



the skull and the nature of the teeth remove them 

 from the Cetacea as much as they approximate them 

 to the Ungulata. In the hippopotamus we have a 

 member of this order nearly converted into an aquatic 

 animal. We must think of the Sirenia as originally 

 emanating from some unknown genera, which probably 

 branched off at a very early period. 



A very uncertain position is occupied by the Hyra- 

 coidae, now represented only by a few species of the 

 genus Hyrax. To say that their characteristics recall 

 at once the Ungulates, the Rodents, and the Insectivora, 

 affords no explanation. Considering the great impor- 

 tance of the molar teeth in deciding derivation, the 

 chief stress should perhaps be laid on their similar- 

 ity in the hyrax and the rhinoceros, and we hence 

 regard the hyrax as an offshoot of an old Ungulate 

 family. 



With respect to the progenitors of the Proboscidae, we 

 refrain from any conjecture. 



Later than the Graminivora,the Carnivora, and espe- 

 cially the beasts of prey, seem to have appeared on the 

 scene of arctic animal life. Granting the possibility 

 (and it is scarcely possible to do otherwise) that pla- 

 cental formations may have originated in various ways, 

 the possibility likewise exists that the Carnivora, and 

 indeed other orders too, such as the Rodents especially, 

 may be direct descendants of carnivorous Marsupials. 

 The oldest beasts of prey known are feline, or resemble 

 the Viverridae and hyenas. Then come the Canidae, 

 and latest of all the Ursidae. In skull, dentition, and 

 extremities, the seals and walruses (Pinnipedea) consti- 

 tute a side branch. Although there can be no idea of 



