8o THE ANIMALS AND MAN 



which are born the great majority are killed before they 

 reach maturity. In a later chapter more attention will 

 be given to this great struggle for life. 



In the preceding paragraph it has been stated that "we 

 know that any living animal has parents; that is, has been 

 produced by other animals which may still be living or be 

 now dead." This is a statement, however, which has found 

 complete acceptance only in modern times. It is a familiar 

 fact that a new kitten comes into the world only through 

 being born; that it is the offspring of parents of its kind. 

 But we may not be personally familiar with the fact that a 

 new starfish comes into the world only as the production 

 of parent starfish, or that a new earthworm can be produced 

 only by other earthworms. But naturalists have proved 

 these statements. All life comes from life; all organisms 

 are produced by other organisms. And new individuals 

 are produced by other individuals of the same kind. That 

 these statements are true all modern observations and 

 investigations of the origin of new individuals prove. But 

 in the days of the earlier naturalists the life of the microscopic 

 organisms like Amoeba and Paramoecium, and even that of 

 many of the larger but unfamiliar animals, was shrouded 

 in mystery. And various and strange beliefs were held 

 regarding the origin of new individuals. 



Spontaneous generation.- -The ancients believed that 

 many animals were spontaneously generated. The early 

 naturalists thought that flies arose by spontaneous generation 

 from the decaying matter of dead animals. Frogs and 

 many insects were thought to be generated spontaneously 

 from mud, and horse-hairs in water were thought to change 

 into water-snakes. But such beliefs were easily shown 

 to be based on error, and have been long discarded by 

 zoologists. But the belief that the microscopic organisms, 

 such as bacteria and infusoria, were spontaneously generated 

 in stagnant water or decaying organic liquids was held by 



