112 THE LIVING WORLD. 



before. Perhaps, loo, the reptiles had expended the most of their 

 energy, so that they were ready to retire before any newcomers. At all 

 events, we find that with the end of the Cretaceous (8) or the begin- 

 ning of the Tertiary (9) the new group of mammals rapidly took the 

 place of reptiles. A large share of the reptiles disappeared and those 

 that remained took a subordinate position compared to that of the 

 new monarchs of the world. With extreme rapidity now did the 

 mammals develop. In no other instance in the animal kingdom has 

 development been so rapid. Expanding into many types, occupying 

 constantly new fields of nature, they soon began to assume forms 

 familiar to us, and our modern families began to appear. The 

 mammal fauna thus became more and more like that existing to- 

 day, until by the end of the Tertiary (9) the mammals of the present 

 period may be said to have been in existence. Finally in the Quar- 

 ternary (io) period there appeared one animal who seized upon a new 

 and untried field of nature for its own. This new field was that of 

 mind, and this new animal soon distanced every other competitor and 

 became immeasurably superior to all other animals. This of course 



