278 THE DOCTRINE OF DESCENT. 



of 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 mem- 

 ber 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 placental for- 

 mations may have originated in various ways, the pos- 

 sibility 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 

 Viverridse and hyenas. Then come the Canidae, and 

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

 ties, the seals and walruses (Pinnipedea) constitute a side 

 branch. Although there can be no idea of any special 



