DIFFERENTIATION OF INDIVIDUALS AND ADAPTATION 141 



13. What are the principal geographical faunas recognized by zoologists. 

 Enumerate the more important means by which dispersal of animals from one 

 region to another occurs. What are the chief barriers to the dispersal of land 

 animals? of aquatic animals? 



14. Study the different authors to which you have access, as to the significance 

 of the terms species and variety (or sub-species). 



15. What were the older views concerning the "fixity" or invariability of 

 species? 



1 6. What are the different views of the "Origin of Species," as based on the 

 views of the meaning of species ? 



17. What is the essential difference between the theories of "natural selection" 

 and "definite variation" as explaining adaptation of organisms to their environ- 

 ment. 



1 8. What additional ideas are introduced by the "mutation" theory of De 

 Vries? What reasons does he give for thinking that natural selection is not a very 

 important factor in adaptation ? 



