278 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- 
coidz, 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 Proboscide, 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 Viverride and hyenas. Then come the Canide, 
and latest of all the Urside. In skull, dentition, and 
extremities, the seals and walruses (Pinnipedea) consti- 
tute a side branch. Although there can be no idea of 
