36 BATEACHIANS. 



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

 development of the Proteus anguinus ; 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 ]S"ewt. The 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 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 integxmient, 

 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 branchise, but breathing air, and in 

 every particular the Reptile." 



But however curious the phenomena attending the development 

 of the tadpoles of the Amphibian Eeptiles 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 internal viscera ; 

 more especially 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 develop- 

 ment through which the embryo of every air-breathing vertebrate 

 animal must pass while concealed within the egg, or yet unborn.* 



* In the British Muaeum Catalogue (1850) these Amphibians are styled Batra- 

 chia Gradientia, and are distributed under three families, comprising fifty-two recog- 

 nised species. The class Amphibia is divided by Dr. Gray into five orders — viz. 

 Batraohia, Fseudosauria, Pseudophidia, Pseudichthyes, and Meantia. Of these the first, 

 or the Batrachia, are divided into the sub-orders Salientia and Gradientia, the latter 

 consisting of three families, Salamandridce, Molgidce, and Plethodontidm. The second 

 order, Pseudosauria, comprises the families Protompsidm (which contains the Sieholdtia 

 maxima) and AmpMumidie. The third order, Pseudophidia, consists of only one 

 family, Cceciliid<e. The fourth order, Pseudichthyes, also contains one family only, 

 the Lepidosirenidee. The fifth order, Meantia, comprises the two families Proteidce 

 and Sirenidce. Twenty-four ascertained species are distributed amongst the last 

 four of these orders ; but the limits of this work do not permit of a more detailed 

 notice of these various groups of Batrachia Gradientia. More recently, Dr. Giinther, 

 in his work on the reptiles of the Indian region, has pointed out certain structural 

 characters connected with the generative system which show that the Pseudophidia 



