194 



EVOLUTION 



The Doctrine of Evolution.- -We have now learned that animal 

 forms may be arranged so as to begin with very simple one-celled 

 forms and culminate 1 with a group which contains man himself. 

 This arrangement is called the evohdionciry series. Evolution means 

 Mammals . , change, and these groups 



are believed by scientists 

 to represent stages in com- 

 plexity of development of 

 life on the earth. Geology 

 teaches that millions of 



'Birds 

 13000 



Reptiles 



Amphibians 

 /14O O 



Fishes 



13000 y ears a s> llfe u P n :he 



earth was very simple, 

 and that gradually more 

 and more complex forms 

 of life appeared, as the 

 rocks formed latest in time 

 show the most highly de- 

 veloped forms of animal 

 life. The great English 

 scientist, Charles Darwin, 



The evolutionary tree. Modified from Gal- from this and other evi- 

 loway. Copy this diagram in your note- den explained the theory 

 book. Explain it as well as you can. 



of evolution. This is the 



belief that simple forms of life on the earth slowly and gradually 

 gave rise to those more complex and that thus ultimately the most 

 complex forms came into existence. 



The Number of Animal Species. - - Over 500,000 species of 

 animals are known to exist to-day, as the following table shows. 



Span &e.s 



^2500 1 



Coelenteratei 

 45OO 



Protozoa 8000 



Protozoa 

 Sponges 

 Coelenterates . 

 Echinoderms . 

 Flatworms 

 Roundworms . 

 Annelids 

 Insects . 

 Myriapods . 



8,000 Arachnids 16,000 



2,500 Crustaceans . . . 16,000 



4,500 Mollusks .... 61,000 



4,000 Fishes . . . . . 13,000 



5,000 Amphibians . . . 1,400 



1,500 Reptiles 3,500 



4,000 Birds 13,000 



360,000 Mammals 3,500 



2,000 Total .... 518,900 



