ORIGIN ‘OF THE WHALES. 261 
Hoofed animals among the Indeciduata. In the same way 
as the river-horse at present stands midway between the 
extreme branches of oxen and sea oxen, the sea otter still 
forms a surviving intermediate stage between the widely 
separated branches of dogs and sea dogs. In both cases 
the complete transformation of the external form, conse- 
quent upon adaptation to entirely different conditions of 
life, has not been able to efface the solid foundation of the 
inherited internal peculiarities. 
According to Huxley’s opinion, which has already been 
quoted, only the Herbivorous Whales (Sirenia) are derived 
from Hoofed animals; on the other hand, the Carnivorous 
Cetacea (Sarcoceta) are derived from the marine animals of 
prey; the Zeuglodonts would form a transition between the 
two latter. But in this case it would be difficult to under- 
stand the close anatomical relations which exist between 
the Herbivorous and Carnivorous Cetacea. The strange 
peculiarities in the internal and external structure which 
so strikingly distinguish the two groups from all other 
mammals would then have to be regarded only as analogies 
(caused by the same kinds of adaptation), not as homologies 
(transmitted from a common primary form). The latter, 
however, strikes me as being by far the more probable, and 
hence I have left all the Cetacea among the Indeciduata as 
one group of kindred origin. 
The remarkable order of Flying Mammals, or Bats 
(Chiroptera), stands near to the Carnaria as well as to the 
Insectivora. It has become strikingly transformed by adap- 
tation to a flying mode of life, just as marine animals of 
prey have become modified by adaptation to a swimming 
mode of life. This order probably also originated out of 
