THE LIVING WORLD 



245 



Then our present whales and porpoises were anticipated 

 by gigantic marine reptiles, ichthyosauri and plesiosauri, 

 while numerous flying reptilian forms, small and large, 

 flitted through the air as bats do now. That time 

 may well be called the age of reptiles. Nevertheless, 

 small beasts had then already begun to make their 

 appearance. 



In early tertiary times creatures existed which more 

 closely resemble forms now living, while in the later 

 tertiaries are entombed the remains of organisms more 



FIG. 52. 



ICHTHYOSAURUS. 



Showing the outline of the dorsal and tail fins, the existence of 

 which has been recently discovered. 



and more like those now living as we examine strata 

 later in date. 



That living organisms have definite relations to space 

 has been already noted and some examples given. 



Each large portion of the earth's surface has, in fact, 

 its special plant population or flora, as it has its 

 special animal population or fauna. For details the 

 student is referred to works on organic geography. 

 Nevertheless it may here be noted that (i) South 

 America, (2) Africa south of the Sahara, (3) Australia 

 and (4) India with its Archipelago, have each an in- 

 teresting and peculiar fauna ; as also that (5) North 



