50 



have much independent testimony, and the known facts all 

 point to extensive migrations of animals over it. 



The Cetacea are connected with the marine Carnivores through 

 the genus Zeughdon, as Huxley has shown, and the points of 

 resemblance are so marked that the affinity cannot be doubted. 

 That the connection was a direct one, however, is hardly prob- 

 able, since the diminutive brain, large number of simple teeth, 

 and reduced limbs in the Whales, all indicate them to be an 

 old type, which doubtless branched off from the more primi- 

 tive stock leading to the Carnivores. Our American extinct 

 Cetaceans, when carefully investigated, promise to throw much 

 light upon the pedigree of these strange mammals. As most 

 of the known forms were probably marine, their distribution is 

 of little service in determining their origin. 



That the Sirenians are allied to the Ungulates, is now gen- 

 erally a'dmitted by anatomists, and the separation of the exist- 

 ing species in distant localities suggests that they are the rem- 

 nants of an extensive group, once widely distributed. The 

 large number of teeth in some forms, the reduced limbs and 

 other characters, point back to an ancestry near that of the 

 earliest ungulates. The gradual loss of teeth in the specialized 

 members of this group, and in the Cetaceans, is quite parallel 

 with the same change in Edentates, as well as in Pterodactyls 

 and Birds. 



The Ungulates are so distinct from other groups that they 

 must be one of the oldest natural divisions of mammals, and 

 they probably originated from some herbivorous marsupial. 

 Their large size, and great numbers during Tertiary and Post- 

 tertiary time, render them most valuable in tracing migrations 

 induced by climate, as well as in showing the changes of 

 structure which such a contest for existence may produce. 



In the review of the extinct Ungulates, I have endeavored 

 to show that quite a number of genera usually supposed to 

 belong originally to the Old World are in reality true Amer- 

 ican types. Among these were the Horse, Rhinoceros, and 

 Tapir, all the existing odd-toed Ungulates, and besides these 



