410 Causes and Course of Organic Evolution 



also of the acknowledged land or fresh-water origin of nearly 

 all vertebrates other than the more recent teleost fishes, and 

 in view finally of the considerations to be presented in the 

 next chapter, the writer is forced to the conclusion that the 

 main and dominant lines of animal evolution have all orig- 

 inated in fresh water or on land, and that only side hnes have 

 assumed a marine life, though these have often branched out 

 profusely into species, and even have given off again groups 

 that have in rare cases returned to a fresh-water or a land 

 life. 



