88 THE ORIGIN OF MAN 



become acquainted and also with the lung-fishes, 

 fishes that had lungs in addition to gills. When 

 the oceans spread over the continents and new 

 lands emerged we have seen how these lung- 

 fishes, due to inadequate amounts of free oxygen 

 in inland waters, and in which these lung-fishes 

 remained, gradually changed into amphibians, 

 animals that in addition to gills had lungs, and 

 that sometimes lived on land and at other times 

 in the waters. We, also at this time, made a 

 comprehensive study of fishes, the first verte- 

 brates and ancestors of our modern mammals. 

 The rise of echnoderms and sharks then occurred, 

 likewise the primitive reptiles and insects, the 

 descendants of the trilobites, the first invertebrate 

 animals. Then came the modern insects and am- 

 monites and first land vertebrates. The dino- 

 saurs made their first appearance at this time and 

 continued to be the dominant animals for a long 

 time. Chief among which was the King Tyrant 

 Saurian, the mightiest flesh eater of all times. 



