238 AMPHIBIANS

particular, but can be made either according to the
food that is discoverable. Naturally the sexes are
in about equal proportions, but by feeding young
tadpoles on beef and frog-flesh it has been found
possible to turn nine out of ten of them into females.

The frogs, as a rule, have ten vertebrz, but Pipa
has only eight. The skeleton is peculiar from the
enormous development of the pelvis, at the upper
end of which comes the hump on the frog’s back.
The bones of the fore-arm and shank are in each
case anchylosed to form a single bone. A frog has
no movable ribs, and hence the gulp with which it
breathes. In fact, it swallows the air much as if it
were water, so that it is possible to suffocate a frog
by merely holding its mouth open. A good deal of
respiration is also done by the skin, and hence if you
butter a frog you cause its death.

CAUDATA.—These are the tailed amphibians,
and there are more than 100 species of them.
Three of these are found in Britain—the crested
newt (Molge cristata), the smooth newt (WZ. vulgaris),
and the palmated newt (7. galmata), all of which live
in the water during spring and summer, and on land
during autumn and winter. Like the salamanders,
they lose their gills before they reach maturity ;
one species, however, the axolotl, retains its gills
throughout. The Salamandride have eyelids, the
Amphiumide have not; they are eel-like creatures,
with small limbs almost at the extreme ends of
their long bodies, and they lose their gills during
metamorphosis, but retain the slit in adult life.