REPTILIA. 



541 



the hind-legs begin to sprout beneath the skin ; and the creature 

 presents in a transitory condition the same external form as that 

 which the Siren tacertina permanently exhibits. 



Fig. 240. 



By the thirty-sixth day the young Salamander (Jig. 240, E) 

 has arrived at the developement of the Proteus anguinus ; its hind- 

 legs are nearly completed, its lungs have become half as long 

 as the trunk x>f its body, and its branchise more complicated in 

 structure. 



At about the forty-second day the tadpole begins to assume the 

 form of an adult Triton (Jig- 240, F) : the whole body becomes 

 shorter, the fringes of the branchise are rapidly obliterated, so that 

 in five days they are reduced to simple prominences covered by 

 the skin of the head ; and the gill-openings at the sides of the neck, 

 which, as in fishes, allowed the water to escape from the mouth, 

 and were in like manner covered with an operculum formed by a 

 fold of the integument, are gradually closed : the membranous fin 

 of the tail contracts, the skin becomes thicker and more deeply 

 coloured, and the creature ultimately assumes the form and habits 

 of the perfect Newt (Jig. 241), no longer possessing branchiae at 

 all, but breathing air, and in every particular completely converted 

 into a Reptile. 



But, however curious the phenomena attending the developement 

 of the tadpoles of the amphibious Reptiles may be to the observer 



