THE SCOPE OF ZOOLOGY 



13 



There was a time when scientists had difficulty in trying to decide 

 if viruses were living or nonliving. When it was discovered that they 

 became adapted to varying environmental conditions through natural 

 selection, it appeared that they should be included in the category of 



living things. 



6. Reproduction. Since living things cannot continue to exist in- 

 definitely as individuals, there must be some method of reproducing 

 other living things like themselves or they will disappear from the face 

 of the earth. In some primitive forms reproduction is very simple; 

 after a period of growth each organism splits itself into two halves, 



Photo by Winchester 



Fig. 1.3. Find the bird. This is a photograph of a Poor Will's Widow on a nest of 

 leaves. The fact that the bird blends so well with its surroundings is no chance occur- 

 rence. It is one of the inherited adaptations which comes about through natural selec- 

 tion. Only living things thus become adapted. 



each of which becomes a complete organism; these grow and divide 

 and the race thus continues its existence. Many plants and some sim- 

 ple animals produce buds, or similar outgrowths from their bodies, 

 which grow into entire new plants or animals. The great majority of 

 living things produce small sex cells which unite with cells from the 

 opposite sex and initiate the life of a new organism. 



It was once believed that living organisms appeared spontaneously 

 from nonliving matter. Maggots were supposed to be generated by 

 decaying meat ; mice and rats were thought to originate from neglected 

 garbage; and frogs were believed to appear from mud in the ponds 



