AMPHIBIA, OR BATRACHIANS. 89 



open up and increase in size. The circulatory organs are corres- 

 p mdingly modified The calibre of the large branchial vessels 

 is diminished, and the pulmonary trunks increase in number 

 and diameter. Later on, the solid parts of the branchial appara- 

 tus disappear also, the bones and cartilages being gradually 

 re-absorbed. Eventually the alteration is fully accomplished, 

 and there remains not the slightest trace of the former branchial 

 apparatus. In this instance, not only has there been trans- 

 formation and substitution, but an actual metamorphosis has 

 oscurred ; for the respiration, which was aquatic before, has 

 become atmospheric, 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 develop- 

 ment. 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 pala- 

 tine arch, and not to the jaw ; the intestine, which before was 

 long, and almost cylindrical, becomes shorter, and is inflated in 

 certain portions of its length ; and the abdomen, which had 

 been almost spherical, becomes thin and slender. The meta- 

 morphose, 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. Beneath 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, 



