"^"^ ZOOGENESIS Hi' 



capable of locomotion, or in some form or other they 

 must be adaptable to transportation by the winds 

 or other agencies. 



Plants are distributed almost exclusively as seeds 

 or spores, chiefly by the winds. But a few seeds are 

 adapted to become attached to the fur of animals and 

 thus to be transported, while some are carried about 

 in various other ways. Animals mostly get about by 

 walking or by flying, either throughout their lives or 

 at some special stage, but some are wind-transported 

 in a spore-like or other special form after the manner 

 of the plants. 



The immobility of the food supply and the necessity 

 of seeking or being carried to it are the chief control- 

 ling features governing all types of life on land. 

 Therefore land animals are almost wholly of those 

 types, arthropods or jointed footed creatures — the in- 

 sects, spiders and their allies — and backboned animals 

 or vertebrates, which are best adapted for locomotion, 

 with a few representatives of some other types with 

 fair locomotor powers, as the mollusks — snails and 

 slugs — and earthworms. 



While powers of active locomotion or else capacity 

 for transportation in some form or other through a 

 medium much lighter than themselves during at least 

 one period of their existence is an essential requisite 

 for all animals living on the land, no such necessities 

 present themselves in the case of the animals living 

 in the sea. 



For water is about 814 times as heavy as air. It is 

 almost as heavy as protoplasm, the material making 



