44 WHAT EVOLUTION IS 



only invertebrates were present. 

 These include sponges, corals, star- 

 fish, worms, crustaceans, insects, 

 brachiopods, snails, clams, and other 

 shellfish. Vertebrates, or backboned 

 animals, first arose about the begin- 

 ning of the last third of the period 

 of life on the globe, and the earliest 

 fossil representatives of this group 

 were the fishes. These were followed, 

 near the opening of the last quarter, by 

 the amphibians which were succeeded 

 by the reptiles, the mammals, and the 

 birds in the order named. Man has 

 been present on the globe during some- 

 what less than the last hundredth of 

 the total period of living things. 



When this sequence is reviewed it 

 is seen at once to present a reasonable 

 plan. Invertebrates precede verte- 

 brates, fishes antedate amphibians 

 and these in turn come before reptiles, 

 mammals, and birds. Man appears 



