TRANSFORMATION Of NZWTS. 33 



by a membrane, distinctly appear. The branchiae, at first simple, 

 are divided into fringes, wherein red blood now circulates ; the mouth 

 has grown very large, and the whole body is so transparent as to 

 reveal the position of the viscera within. Its activity is likewise 

 much increased ; it swims with rapidity, and darts upon minute 

 aquatic insects, which it seizes and devours. 



" About the twenty-second day the tadpole for the first time begins 

 to emit air from the mouth, showing that the lungs have begun to 

 be developed. The branchiae are still large. The fingers upon the 

 fore-legs are completely formed. 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 lacertina permanently 

 exhibits. 



" By the thirty-sixth day the young Salamander has arrived at the 

 development of the Proteus angiiinus ; its hind-legs are nearly 

 completed ; its lungs have become half as long as the trunk of the 

 body, and its branchiae more complicated in structure. 



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

 form of an adult Newt The body becomes shorter, the fringes 

 of the branchiae are rapidly obliterated, so that in five days they 

 are reduced to simple prominences covered by the skin of the head ; 

 and the gills, opening at the sides of the neck, which allowed the 

 water to escape from the mouth, as in Fishes, and were, like them, 

 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, no 

 longer possessing branchiae, but breathing air, and in every particular 

 the reptile. " 



But however curious the phenomena attending the development 

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

 who merely watches the changes perceptible from day to day in their 

 external form, they acquire tenfold interest to the physiologist who 

 traces the progressive evolution of their viscera. Especially this is 

 the case when he finds that in these creatures he has an opportunity 

 afforded him of contemplating, displayed before his eyes as it were 

 upon an enlarged scale, those phases of development through which 

 tne embryo of every air-breathing vertebrate animal must pass while 

 concealed within the egg or yet unborn. 



"One of the most interesting of the Mexican Amphibians," writes 

 Prof. Martin Duncan, " is the so-called Axolotl, or Siredon, which 

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