TRANSFORMATION OF NEWTS. 33 
by a membrane, distinctly appear. The branchiee, 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 branchiz 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 Szven acertina permanently 
exhibits. 
“ 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 branchize 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 branchiz 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 branchize, 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 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 development through which 
the embryo of every air-breathing vertebrate animal must pass while 
concealed within the egg or yet unborn.* 
* In the British Museum Catalogue (1850) these Amphibians are styled Batra- 
chia Gradientia, and are distributed under three families, comprising fifty-two 
