3 oo 



ELEMENTARY ZOOLOGY. 



outside the loss of the tail, the loss of gills, the develop- 

 ment of legs, and a corresponding change in the shape of 

 the body. Within, the changes are just as profound. 

 The lungs develop, the circulation changes, the long 

 coiled digestive tract suited to vegetable feeding becomes 

 relatively shorter and adapted to the adult diet; the 



FIG. 118. The metamorphosis of the frog. After Brehm. 

 of stages. 



bers indicate sequence 



Questions on the Figure. How much of the egg is really ovum? 

 Enumerate the changes that take place in passing through the 

 various stages? In what order do the legs appear? How is respi- 

 ration effected after stage 6 ? After stage 1 1 ? 



sexual organs develop. All this takes place while the 

 animal is actively living and using all its powers. It 

 does not go into a resting stage as do many of the insects. 

 This change is made in the life-history of a single indi- 

 vidual. Zoologists believe that the ancestors of the 

 higher air-breathing forms were originally water-breath- 

 ers, and that, through long series of generations, they 



