OF EVOLUTION. 65 



Camelus is held by the Pliocene genus Pliau- 

 chenia, which possesses but three premolars in 

 the lower jaw, while nearly the extreme term 

 of reduction in this part of the dental series is 

 found in the late Pliocene and recent llamas 

 (Auchenia), which retain but two premolars in 

 the upper jaw and a single one in the lower 

 jaw. Finally, in the nearly contemporary genus 

 Holomeniscus, which embraced animal forms fully 

 equalling the camel in size, and ranging from 

 Oregon to the valley of Mexico, there is but a 

 single premolar left to each side of either jaw. 



The eliminative development that has here 

 been traced corresponds very closely with the 

 conditions presented by the living animal in 

 passing from its embryonic to its adult condi- 

 tion. Thus, in the foetal condition of probably all 

 ruminants the metapodial bones are distinct, as in 

 the early Poebrotherium ; moreover, the animals 

 are provided with cutting teeth in the upper 

 ja\v, in the manner of their ancient progenitors. 



Professor Cope, who has given close attention to 



(5) 



