LATEE LIFE ON THE EAKTH 59 



cene ; where, amongst others, we find the living 

 genus Hylobates (gibbon). Man probably origi- 

 nated in the 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 Anchitherium, of the Miocene, to 

 Hipparion and Equus 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 its 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 



