EVOLUTION 



123 



and which by gills. This complicated way of growing into 

 a frog is called metamorphosis and this term lias the same 

 general meaning that it did when used to describe tin; 

 growth of insects (page 16). 



The tadpoles of leopard frogs become small frogs 

 in a single summer, but the tadpoles of bullfrogs and 



Figure 122. — Two Stages in the Development of Tadpoles. 



green frogs require two seasons to complete their develop- 

 ment. These latter tadpoles hibernate in the mud with 

 adult frogs and toads. 



122. Evolution. — Evolution, in a larger sense, is the 

 theory or belief that all of the complex animals and plants 

 on earth to-day developed from the simpler animals and 

 plants of many generations ago. This theory tries to 

 prove itself through the careful study and investigation 

 of the relationships between animals and plants of the 

 present and those that formerly existed. 



The study of the changes through which the egg of the 

 frog grows into a tadpole and then into a frog tells us 



