194 



EVOLUTION 



Mammals 



"Birds 

 13000 



Reptiles 

 03500 



Amphibians 

 /l400 



Fishes 

 13000 



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 with a group which contains man himself. 

 This arrangement is called the evolutionary series. Evolution means 



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 

 years ago, life upon the 

 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, 

 from this and other evi- 

 dence, explained the theory 

 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 showSc 



Crustacea f 16 000 



Myrh 



4000\fooO. 



Annelids ' 



Echinoderms^^^^f^^\ J 



Flat ^ormsSOQLj^ 



Sponges 



' "^2500/ 



Coelenterates 

 4500 



Protozoa 8000 



The evolutionary tree. Modified from Gal- 

 loway. Copy this diagram in your note- 

 book. Explain it as well as you can. 



Protozoa 



Sponges 



Coelenterates 



Echinoderms 



Flatworms 



Roundworms 



Annelids 



Insects . . 



Myriapods . 



16,000 



16,000 



61,000 



13,000 



1,400 



3,500 



13,000 



3,500 



518,900 



