316 LEISURE-TIME STUDIES. 



organs in the form of external gills in early life ; facts well 

 known to any one who has seen a young frog in its tadpole 

 stage, and who has had the curiosity to watch the trans- 

 formation of the tadpole (Fig. 62) into the adult frog. All 

 amphibians further possess lungs in their fully grown con- 

 dition, whether the gills of early life persist or not. Thus the 

 curious lizard-like proteus, found in the caves of Adelsberg, 

 and the still more curious axolotl of Mexico, exemplify newt- 

 like creatures which retain the gills of early life, and breathe 

 by these organs as well as by the lungs with which they 

 are provided in their adult shape. The common newts of 

 our ponds and ditches, the land-newts of other countries, 

 and the frogs and toads breathe, on the contrary, by lungs 

 alone in their perfect condition ; the gills of early life being 

 discarded when these creatures assume terrestrial habits. 

 Thus the newts, although living essentially in water, breathe 

 like the frogs by lungs alone in their adult state ; and, like 

 the aquatic and lung-bearing whales, have to ascend periodi- 

 cally to the surface for a supply of atmospheric air. 



Bearing these characters of this group of animals in 



FIG. 63. The axolotl (Siredonpisciformc), showing the external gills. 



mind, the curious nature of the changes through which 

 certain of its members pass may be fully realised. The 

 axolotl (Siredon pisciformc, Fig. 63) is a creature inhabiting 



