^^ ZOOGENESIS ^1^ 



until the whole strain gradually or suddenly died out. 

 In the larger major groups this process occurred at 

 the same time, or at different times, in many dif- 

 ferent types. 



Such a developmental or evolutionary process is 

 well represented by a branching or tree-like figure in 

 which each branch end represents a special line which 

 has become extinct. An excellent example of this is 

 seen in the developmental history of the horses. 



This process of branching or tree-like development 

 of many different animal forms from a single original 

 type — as for instance the development of all the dif- 

 ferent kinds of dogs we know today from the original 

 wolf — is commonly known as evolution. 



Eoge7iesis and evolution. — What is the relation of evo- 

 lution to eogenesis — the simultaneous formation 

 through following different developmental paths from 

 the primitive single cell of all the major types of 

 animals? 



Through eogenesis the ground is prepared for the 

 growth of the evolutionary trees. Therefore the pic- 

 ture that we get shows a whole forest of evolutionary 

 trees of widely different sizes each of which arose 

 from a seed formed and planted by the process of 

 eogenesis. 



Broader aspect of the development of animal forms. — The 

 evolutionary processes by which are formed the ulti- 

 mate twigs of the various evolutionary trees are 

 processes of specialization through the progressive 

 suppression of certain features, leading secondarily 

 to the emphasis of others. The more extreme the 



