103 CRITIQUES AND ADDRESSES. [IK. 



forms of Hyopotamus and Cliceropotamus ; but Hyo- 

 potamus appears to have had only two toes. 



Again, all the great groups of the Ruminants, the 

 Bovidce, Antilopida, Camelopardalidce, and Cervida, 

 are represented in the Miocene epoch, and so are the 

 Camels. The Upper Eocene Anoplotherium, which is in- 

 tercalary between the Pigs and the Trayulidce, has only 

 two or, at most, three toes. Among the scanty mammals 

 of the Lower Eocene formation we have the perisso- 

 dactyle Ungulata represented by Coryphodon, Hyra- 

 cotherium, and Pliolophus. Suppose for a moment, for 

 the sake of following out the argument, that Pliolophus 

 represents the primary stock of the Perissodactyles, and 

 Dichobune that of the Artiodactyles (though I am far 

 from saying that such is the case), then we find, in the 

 earliest fauna of the Eocene epoch to which our investiga- 

 tions carry us, the two divisions of the Ungulata com- 

 pletely differentiated, and no trace of any common stock 

 of both, or of five-toed predecessors to either. With the 

 case of the Horses before us, justifying a belief in the 

 production of new animal forms by modification of old 

 ones, I see no escape from the necessity of seeking for 

 these ancestors of the Ungulata beyond the limits of the 

 Tertiary formations. 



I could as soon admit special creation, at once, as 

 suppose that the Perissodactyles and Artiodactyles had 

 no five-toed ancestors. And when we consider how large 

 a portion of the Tertiary period elapsed before Anchi- 

 tJierium was converted into Equus, it is difficult to escape 

 the conclusion that a large proportion of time anterior to 

 the Tertiary period must have been expended in convert- 

 ing the common stock of the Ungulata into Perisso- 

 dactyles and Artiodactyles. 



The same moral is inculcated by the study of every 

 other order of Tertiary monodelphous Mammalia. Each 



