^^ ZOOGENESIS 



While this series of horse types may broadly speak- 

 ing be considered as representing a single line running 

 from the little four-toed horses to the large single-toed 

 horses, the actual conditions really are not quite 

 so simple. 



Several of the horse types after their first appearance 

 branched out in various directions, and these diverse 

 branches became more and more distinct from each 

 other and themselves gave off branches in the same 

 way, and again the process v^as repeated. 



In the Pleistocene the modern type of horse, w^hich 

 was then of relatively recent appearance, had already 

 branched out in many different directions. At the 

 present time there exist a single sort of true wild 

 horse in Asia, four kinds of wild donkeys, three in 

 Asia and one in Abyssinia (Ethiopia), and several 

 different kinds of zebras, all in Africa. 



The development or evolution of the horse from its 

 first beginnings in the Eocene to the present day may 

 thus be most faithfully represented by a tree-like 

 figure, the base of the tree-like figure being a creature 

 more or less closely resembling EoJhippus, and the 

 present wild horses, wild asses and zebras being repre- 

 sented by a few of the topmost twigs. 



The existence of many well marked develop- 

 mental trees like that delineated by the fossil 

 horses enables us to present a general picture of the 

 evolutionary history of many different types of ani- 

 mal life. 



Large sections of certain groups of animals may 

 even be delineated in this way and their evolutionary 



