THE COMMON FROG. 89 



instance, not only has there been transformation and substi- 

 tution, but an actual metamorphosis has occurred ; for the 

 respiration, which was aquatic before, has become atmo- 

 spheric, and, strictly speaking, the animal from having been 

 a fish has been converted into a batrachian. 



If we examine any particular apparatus, we shall find it 

 also presenting many curious phenomena in the course of 

 its development. We shall find that as the herbivorous 

 habits give place to carnivorous ones, the digestive apparatus 

 undergoes a change adapting it to the new form of diet. 

 The mouth increases in size and gape ; the little beak- 

 organs, or more correctly, the horny lips, are replaced by 

 teeth, which are attached to the palatine arch, and not to 

 the jaw ; the intestine, which before was long and almost 

 cylindrical, becomes shorter, and is inflated in certain por- 

 tions of its length ; and the abdomen, which had been 

 almost spherical, becomes thin and slender. The meta- 

 morphoses may now be seen in its entire extent, and more 

 distinctly as regards the locomotive system than any other. 



The tadpole at first exhibits no trace of either internal or 

 external limbs. It swims about like a fish by the action of 

 its tail, which is an extensive organ, longer and wider than 

 the body, supported by a prolongation of the vertebral 

 column, moved by powerful muscles, and supplied with 

 large blood-vessels and numerous nervous branches. Be- 

 neath the skin and muscles of the anterior and posterior 

 regions of the body, two little projections appear at a certain 

 period. These are the limbs, and are at first attached to 

 the adjacent structures by the nerves and blood-vessels 

 which are supplied to them. These projections increase in 

 size, their appendages appear in due course, and eventually 

 the hip and shoulder bones are developed. As soon as these 

 locomotive organs enter upon the discharge of their functions, 

 the tail begins to disappear. Its skin, muscles, nerves, 

 bones, and blood-vessels atrophy, and vanish from our 

 sight. They have not faded away, they have not simply 



