CHAPTEE III 



LATER LIFE ON THE EARTH 



THE commencement of the Deutozoic, or newer 

 Palaeozoic era, forms a very convenient division in 

 the progress of life ; for before that time biological 

 development took place almost entirely in the ocean, 

 and it is not until we come near the close of the older 

 Palaeozoic that we find any trace of land animals. 

 But when we pass to the second half, embracing the 

 time from the commencement of the Devonian to the 

 Pleistocene, we shall find that our attention will be 

 almost entirely directed to the land. 



Of course , during this time organic evolution went 

 on steadily in the ocean also ; but no new types 

 appeared there, except some air-breathing verte- 

 brates which were descended from land animals. 

 The simple and lowly forms of the Palaeozoic era, 

 which came first in the ocean, did not altogether die 

 out ; for a type once introduced almost always con- 

 tinued to exist. But the various species and genera 

 that is, the particular shapes which represented 

 the type changed; each, after living a certain 

 time, became extinct, and gave place to its suc- 

 cessors. Usually the simple types continued, living 

 side by side with the more complex or higher types , 

 which successively came into existence ; so that life 



39 



