GENERAL ZOOLOGICAL FACTS AND THEORIES 277 



TABLE XIV 



THE FOUR KINDS OF FAUNA AND THEIR MODES OF EXISTENCE 





THE LAW OF DISPERSION. Animals tend to migrate from the 

 region of their origin. The reason for this is in dispute at the 

 present time. It has been held for many years that every animal 

 produces a greater number of offspring than can be supported 

 in its particular habitat, and, since parents and offspring cannot 

 occupy the same area, some individuals must either migrate or 

 die. There are many scientists, on the other hand, who believe 

 that no overcrowding takes place, but that dispersion is the 

 result of a search for food. 



Each species of animal is supposed to have originated in a defi- 

 nite region of the earth's surface, and to have migrated in various 

 directions, enlarging its habitat year by year until an approxi- 



