5^ ELEMENTARY ZOOLOGY 



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 earth- 

 worm 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 Paramcecium, 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 genera- 

 tion from the decaying matter of dead animals. Frogs 

 and many insects were thought to be generated spontane- 

 ously 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 micro- 

 scopic organisms, such as bacteria and infusoria, were 



