TO THE FROG STATE. 17 



by the completed development of the lungs. The 

 gills disappear not because they cease to be used, but 

 they cease to be used because they shrink and 

 disappear by a law of the economy of the frog ; whilst 

 by the same law lungs are developed and the animal 

 breathes air. Lungs thus come into use beca^ise they 

 have come into existence, not because the animal first 

 accustoms itself to live on land and breathe air. 



It is when the fore legs become free and the 

 animal thereby fitted for progression on land, that the 

 tail shrinks and disappears, and the gills for respira- 

 tion in water are superseded by lungs for breathing 

 air. It is not until the fore legs have become deve- 

 loped that the young frog is able to make its way out 

 of the water to breathe air. If by accident the 

 animal, now in the frog phase of development, cannot 

 get a footing on dry land, it is liable to be drowned 

 just as surely as the tadpole was to die from asphyxia, 

 like a fish, if taken out of the water. No sooner 

 does the young frog reach dry land than it begins to 

 jump, its strong hind legs being already fitted for 

 the purpose without any previous practice, except in 

 swimming before it left the water. 



We thus see that in the process of metamorphosis 

 the young frog is structurally prepared for its new 

 conditions of life. The tadpole is not first placed in 

 the new conditions and then has its structure changed 

 under the influence of those conditions in order to 

 be adapted to them. All parts of the structure of 

 the frog being in conformity, one change in the 



c 



