36 GENERAL ZOOLOGY 



to the cycle. Every animal must run in the race of life; 

 and the goal for all is the same death.* 



5. Reproduction. All living things have the power to 

 perpetuate their race. Some animals split themselves in 

 two, or break up into fragments, and each of the pieces 

 grows into a complete new individual. Such multiplica- 

 tion increases the number of organisms easily and quickly. 

 At times, however, most animals have some means of proper 

 reproduction during which there is fusion of products 

 from two individuals to form a third and this new indi- 

 vidual starts out with all the vigor of youth, though its 

 parents may have been at the other end of the cycle. 



6. Adaptability or Reactiveness. All organisms are able 

 to adjust themselves to their surroundings and this ability 

 to meet changing conditions is perhaps the most character- 

 istic attribute of living things. Garden spiders always 

 spin webs of the same type, yet one may fill a square, and 

 another a triangular space. Individuality is thus retained 

 but adapted to varying conditions. The success of any man 

 depends upon his adaptability how well he can meet the 

 difficulties and changing conditions of life. 



* Except in some Protozoa, which may escape death from old age by 

 becoming young again (see Chapter XII). 



