46 THE COMMON FROG. [chap. 



four limbs, and in other respects more or less resembles 

 in appearance, as it does in size, the genus Menopoma 

 before noticed. 



Finally there is a genus of this order {Urodela) 

 which has of late presented circumstances of peculiar 

 interest. This is the Axolotl of Mexico, which was 

 long considered by Cuvier to be a large Eft-tadpole, 

 possessing as it does permanent gills and gill-openings, 

 with some other characters common to the Eft-tadpole 

 stage of existence. At length, however, its mature 

 condition was considered to be established by the 

 discovery that it possesses perfect powers of repro- 

 ducing its kind. 



For some years, individuals of this species have 

 been preserved in the Jardin des Plantes at Paris, and 

 a i^sN years ago one individual amongst others there 

 kept was observed, to the astonishment of its guardian, 

 to have transformed itself into a creature of quite 

 another genus — the genus Ambly stoma, one rich in 

 American species. Since then several other individuals 

 have transformed themselves, but without affording 

 any clue as to the conditions which determine this 

 change — a change remarkable indeed, resulting as it 

 docs not merely in the loss of gills and the closing 

 up of the gill-openings, but in great changes with 

 respect to the skull, the dentition, and other important 

 structures. 



There is, moreover, another and very singular fact 

 connected with this transformation. It is that no one 

 of the individuals transformed (although we must 

 suppose that by such transformation it has attained its 

 highest development and perfection) has ever yet 



