FBOGS AND TOADS. 
275 
Class of animals whose scientific appellation wc have in- 
scribed at the head of this chapter. They thus afford a 
beautiful link in that tissuo of “ chain-mail" which consti- 
tutes the Plan of Nature; for they evidently hold an in- 
termediate position between the Fishes, whose respiration 
is exclusively aquatic, and the truo Reptiles, in which 
this vital function is exclusively aerial. 
Let us look a little more closely at this curious point, — 
the metamorphosis which the Amphibia undergo, and the 
accompanying change in the character of their breathing- 
organs. In the month of April, in almost every ditch 
and pool in the country, we see large masses of clear jelly, 
with black dots distributed at even distances throughout, 
or long strings of the same substance, in which the black 
dots are arranged in a double row. The former is the 
spawn of the Frog, the latter that of the Toad ; and each 
dot is the maturing embryo of a single egg, which latter 
is a clear globe of about one-fifth of an inch in diameter. 
When the spawn is laid, the embryo is an opaque globule, 
darker at one side than at the other. In a few days, 
however, this begins to take the form of an animal — the 
head, the body, and the tail being distinct, as the little 
creature lies ou its side within the egg, coiled up in a 
semicircle. Soon a kind of wart buds from each side of 
the neck — the future gills ; and currents of water are seen 
to stream to and from these important, but as yet minute, 
organs. 
As time passes, the gills divide into branches, the nos- 
trils and the eyes appear, and traces of the mouth may be 
discerned. Meanwhile, the power of voluntary movement, 
at first confined to the head and tail, increases • and the 
