THE FROG. 113 



by a colorless, mucilaginous substance. Now, if we 

 watch the development of these eggs we find that they 

 give birth, not to frogs, but to small beings known as 

 tadpoles, organized, like fishes, for an entirely aquatic 

 life. An elongated ball containing the head and body; 

 a long tail, flattened on the sides ; neither limbs nor 

 fins ; external respiratory apparatus, consisting of little 

 bags or branchiaB on each side of the head; a mouth 

 adapted only for vegetable food : such is the general 

 appearance of an amphibian in the tadpole state. The 

 animal retains this form during a longer or shorter time, 



FIG. 63. 



METAMORPHOSES OF THE FROG. A, frog's eggs; B, tadpole, first without feet; 

 C, the two hindfeet appear ; D, the two forefeet appear; E, the animal has 

 four feet and a tail ; F, the tail disappears, the animal is perfect. 



according to the species, and depending on external con- 

 ditions. Then the limbs begin to appear and become 

 developed ; the form changes ; the head becomes out- 

 lined ; the tail either disappears entirely, as in frogs and 

 toads, or remains, as in the salamander ; the branchiaB 

 shrink away and are obliterated, and the lungs develop. 

 Now the animal begins to seek the air ; it nourishes itself 

 by preference on worms, insects, arid little mollusks. It 

 abandons the water as its constant home ; sometimes, as 

 in the toad, it gives up aquatic life entirely, selecting as 

 its abode a damp hole in an old wall or a cool place under 

 stones, and only returning to the water in order to de- 

 h JO* 



