BRITISH FROGS 
restriction of watery environment will often make 
Amblystomas out of axolotls. The case of the axolotl 
is not so unique as was once thought. “ Neoteny,” as 
this extension of childhood is scientifically called, both 
occurs normally, and can be produced in various am- 
phibia. Even in frogs, the tadpoles can in the case of 
some species be compelled to remain tadpoles for a long 
if not indefinite period of time, behaving, however, pre- 
cisely as tadpoles, though swollen in bulk; the two 
frogs of this country, viz. Rana temporaria and R. escu- 
lenta, are instances to the point. But these tadpoles, if 
they do not ultimately become frogs, die as tadpoles 
without begetting fresh tadpoles. The axolotl and the 
common newt of this country, as well as other newts in 
the strict sense, that is to say, of the genus Triton, not 
only retain their larval characters, but are able, as we 
have seen, to breed as such. ‘These facts lead us to 
some highly interesting conclusions. It used to be a 
common idea, which had the advantage of seeming 
quite philosophical, that the existence of external 
arborescent breathing organs in such amphibians as 
the axolotl and the Japanese salamander, were proofs 
of the antiquity of these forms. The retention of the 
fish-like mode of breathing by gills seemed to argue a 
basal position in the amphibian world. Not so, how- 
ever, do we now think. For it is clear that some at 
least of the gilled forms are merely precociously de- 
veloped young, which, taking time by the forelock, 
commence breeding before structural maturity, and 
that others, like the Japanese salamander, may be 
(here we can only guess for the present) entirely similar 
in origin. Hence it is clearly a recent modification 
which we are dealing with; and therefore the types 
which, like the frog, have not given rise to a persistent 
and sexual larval form are the older. 
Cortez, when he descended from his “‘ peak in Darien,” 
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