THE PROGRESS OF LIFE 91 



Pliocene, somewhere in Central or Southern Asia ; but 

 it is not until the Pleistocene that human relics 

 become abundant. The line of descent of the sea- 

 cows (Sirenia), which date from the Eocene, is quite 

 unknown. 



Several of the smaller groups of mammals have 

 been worked out in great detail. Professor Cope has 

 shewn the genealogy, in North America, of the living 

 camels and llamas from Poebrotherium of the lower 

 Miocene. The ancestors of the horse have also been 

 traced from the five-toed Phenacodus of the lowest 

 Eocene, through the four-toed Hyracotherium and the 

 three-toed AnchUherium, of the Miocene, to Hipparion 

 and Egpius of the Pliocene. 



It has also been found that in several deer the 

 course of development of the antlers, in each indi- 

 vidual, recapitulates the forms of the antlers of its 

 ancestors. Thus, at the present day, the young red- 

 deer at the end of its first year has a simple un- 

 branched antler placed on a short pedicel. At the 

 end of its second year the new antler is two-pronged, 

 and at the end of the third year it consists of a beam 

 or stem with two or three tines or prongs. And this 

 gets more complex year after year. Now, in the 

 lower Miocene, Procervulus had simple horns, which 

 were not shed. Then came the true deer, in which 

 the horn became a long pedicel with a two-branched 

 deciduous antler at the end. At a later period the 

 pedicel was shorter, and the antler longer, consisting of 

 a stem and two branches or tines ; and it is not until 

 we reach the upper Pliocene that we find complicated 

 branching antlers. 



Dogs, cats, oxen, and the goat are first known in 



