178 
ZOOLOOT. 
coiled in a close spiral. 
The mouth is small (Fig. 225, A)y 
with no tongue and only horny 
toothless jaws. The vertebrae of 
the tadpole are biconcave as in 
fishes, afterwards becoming con- 
verted into cup-and-ball joints. 
The accompanying figures rep- 
resent the external changes of the 
toad from the time it is hatched 
until the form of the adult is at- 
tained. The tadpoles of our Amer- 
ican toad are smaller and blacker 
in all stages of growth than those 
of the frog. The tadpole is at 
first without any limbs (Fig. 226, 
Fig. 225.— Mouth and digestive A), and with tvvo pairs of Sfills: 
canal of a Tadpole. ^, mouth; i • i • i t / 
6, intestine coiled on itself; c, SOOn the hinder pair bud OUt. 
c7e^as\ '^/,^'TMhneSy^' ffi this stagc {B) is reached, 
legs; ^, rectum. ^^^^ ^^^^^^ diminish in 
size. Then the fore-legs grow out (C); and finally, as at D, 
the tail is mostly absorbed, and at E we see the little toad 
which hops about on the bank. 
G D E 
FiQ. 226.— Different stages of the Toad. 
There are nearly 700 species of this class now living, of 
which 101 are IsTorth American. 
The.Batrachians are an old-fashioned type* certain fossil, 
extinct tailed forms were as large as whales^ being over 
thirty feet in length. 
