32 STORY OF THE AMPHIBIANS 



ing tailed forms lay their packets under damp moss 

 or stones, etc. ; and here their young are hatched, and 

 in some cases they never go to the water. They 

 begin at once a terrestrial life, though the gills, which 

 they have at first, show their aquatic origin. 



Tadpoles 



Generally speaking, tlie eggs of amphibians (Fig. 

 17) are hatched by the sun's heat. At first the little 

 amphibian in its egg shows as a bloody streak, and 

 appears to develop in its early stages much as a little 

 fish. Later, however, it absorbs all the yolk into the 

 stomach and does not have it suspended below the 

 body as have the little fishes. From the egg the tad- 

 pole breaks away to liberty, if in the water, as a small 

 plump beanlike body with a round sucking mouth and 

 a slim wiggling tail. At first no gills are seen, but 

 soon they grow as branches outside of the neck. Later 

 these are lost, a hole is formed in the neck for breath- 

 ing by gills that are developed inside — as in the fishes 

 — a pretty strong hint that the amphibian did not get 

 its gills from the present kind of fishes. This con- 

 dition prevails only where the creature is going to be 

 a land-haunter to any extent, as in the frog-forms and 

 the salamanders. If it be destined to remain in the 

 water, as in the case of sirens, mud-puppies (" water- 

 dogs "), etc., these outside gills remain, and no inside 

 ones are formed. Finally in the adult frog-forms and 

 in the more upland tailed forms the holes on the side 

 of the neck close, and the creatures become lung- 

 breathers only. While no amphibian may wholly 



