1 84 THE INFANCY OF ANIMALS 



Profound changes now take place. The walls of the 

 back of the throat grow inwardly, and soon meet one 

 another in the middle line to form two tubes — an upper, 

 or gullet for the passage of food for the stomach, and a 

 lower, or windpipe, from the lower end of which the lungs 

 are formed. The young tadpole now comes frequently to 

 the top of the water for air. For the gills are fast de- 

 creasing in size, and are accordingly unable to suffice for 

 the fish-like fashion of breathing, while the lungs are as 

 yet not large enough to serve as efficient respiratory organs 

 for the absorption of atmospheric air. 



A fortnight or three weeks later a critical stage is reached. 

 The normal processes of life are suspended pending ex- 

 tensive and profound structural alterations. The tadpole 

 ceases to feed, the outer layer of the skin is cast, and with 

 this go the gills ; the horny jaws are shed, the large frilled 

 •lips shrivel up, the mouth loses its round shape and assumes 

 the broad cleft characteristic of the frog ; the tongue 

 becomes enormously increased; the eyes, so far concealed be- 

 neath the skin, are now exposed. The abdomen shrinks, the 

 stomach enlarges ; the gut, till now a long tube coiled like 

 a watch-spring and visible through the skin, is reduced to a 

 relatively short irregularly coiled tube, and from a vegetable 

 and carrion feeder the animal now becomes a carnivore, 

 preying only upon living animals such as worms and insects. 



While these internal changes are going on the fore-limbs 

 appear : the left foot being thrust through the hole which 

 served as the exit for the water Used for breathing, while 

 the right bursts through the now degenerate skin. During 

 this enforced fast the nourishment necessary to sustain 

 not only life, but these remarkable changes, has been 

 furnished by the tail, now no longer necessary. All that 

 now remains is a small stump, the last evidence of the 



