268 ' FEOGS AND TADPOLES. 



their way out. They are therefore a little later in making their 

 appearance. The tadpole thus masquerades for a short period as 

 fish with legs. It has not yet reached its full development, but 

 continues to grow for some time longer, and about two months 

 from the laying of the egg, lungs commence to be formed. The 

 details of the alteration of circulation necessitated by the change 

 from a Gill-breather to a Lung-breather are important. As the 

 lungs get larger and larger, the gills decrease in importance, and 

 towards the close of another three weeks a distinct metamor- 

 phosis takes place, — the fish condition is abandoned and the 

 mature amphibian stage adopted. 

 The Tadpole ceases to feed. 



It casts off its outer skin, as well as the horny jaws. 

 The mouth becomes wider and the tongue larger and longer. 

 The eyes come to the surface. 

 The front legs become apparent. 

 - The stomach and intestines become adapted for carnivorous 

 existence. 

 The gills gradually become absorbed and the gill clefts close. 

 As the gills become of less and less importance a pair 

 of bladder-like lungs are formed. 

 The tail is gradually absorbed. 



The Tadpole becomes a carnivorous feeder and is now a verit- 

 able Frog. 



We have thus traced the development of a frog through suc- 

 cessive changes from a single cell, showing how any animal, in 

 the various stages of development which it undergoes, simply 

 repeats the ancestral history of its race, or, as Prof. Marshall 

 neatly puts it, " Climbs up its own genealogical tree." It must 

 therefore be supposed that it has sprung originally from an 

 ancestor living in a unicellular condition throughout its life. 

 But if you ask me whether I consider a Frog is descended from 

 a Jelly-fish or from a Hydra, I must answer, " Certainly not." 

 This would be as absurd as to say that Man is descended from a 

 Monkey, whereas the only contention is that both are descended 

 from a common ancestor. 



It will be allowed, that the condition of the earth when life 



