The Butler County press. [volume] (Hamilton, Ohio) 1900-1946, 1914-07-24
EVOLUTION OF A P0LLYWOG.

Changes That Mark the Transition OF
This Curious Creature From an
Aquatic to an Air Breathing Animal.
How 1t Differs From the Toad.
There is no more interesting creature
on earth than pollywog. or tadpole,
for 1t is fish In the process of trans
formation into a land animal. The
whole process can be watched If you
put a few pollywogs in a milk bottle
Or jar full of water with some water
plants.
In any of the ponds in the parks III
the cities or in the pools in the suburbs
In the proper season frog spawn car
be found 1t floats on the water like
masses of sago pudding. A handful
of this will furnish entertainment for
several weeks and will at the same
time give a lesson in evolution.
The spawn that floats on the ponds
is the eggs of frogs. They lay it in
the first warm days of spring, spread
ing it where the rays of the sun will
warm it. Each egg contains yolk,
which is the food of the living germ
within, and is coated with black, prob
ably to attract as much heat as pos
sible and at the same time to protect
the germ from the penetrating ultra
violet rays of the light, which would
destroy 1t. The black yolk is In the
center of a mass of transparent jelly.
which is there as a protective covering
If small mass of spawn be placed
in a jar Of water and watched daily
with an ordinary magnifying glass the
black yolk Of each egg will presently
be seen to assume sausage-like shape
Gradually this takes the form of tiny
pollywog, which soon begins to wrig-
gle. After few days these little black
bodies wriggle out through the trans
parent jelly and attach themselves to
bits of green sticks or weeds, which
should be placed in the jar with them.
For some time they remain attached
to such supports by sucker, waiting
for the opening Of the mouth. AS yet
there are no visible eyes, but small
stumps on each side of the head will
be noticed. These are the gills. The
whole skin II examined with a lens
will be found to be covered with sort
of animated velvet pile, for its compo-
nent threads are in constant motion,
thereby creating a stream Of fresh wa
ter to carry on the work of breathing
and little later these movements will
be strong enough to bear the body
slowly along, so that locomotion at this
stage is like that of the owliest of liv-
ing creatures. the protozoa.
When the mouth appears the inside
of the great f1eshy lips and the jaws
will be found to be armed with rows
of horny teeth numbering many hun
dreds. The glIs will also have grown
considerably. These, however. soon
give place to internal gills, and the
water taken at the mouth passes out
again by small funnel on the right
side of the head This fishlike stage
disappears with the appearance of the
forelegs.
The hind legs next appear, and as
these develop the mouth is closed for
alterations. No food can be taken. and
during this enforced fast the tadpole
supports life by consuming its tail.
This is slowly digested by a process
not yet clearly understood By the
time this strange feast has ended the
new mouth and the lungs have ap-
peared-the tadpole has become a frog
and leaves the water for the land AS
a tadpole 1t fed by rasping off vegeta-
BILE and animal matter with its teeth;
as a frog it feeds by jerking food into
its capacious mouth by the flick of a
very sticky tongue.
Nevis and toads In their pollywog
stage can scarcely be told from frogs,
but nevis remain water animals, wear
ing tails, all their life. Some Of them
retain their gils also, but most Of them
develop lungs and have to come to the
surface to breathe. There are few spe-
cies which have neither gills nor lungs
and therefore do not breathe at all,
their blood being oxidized by the skin
alone.
Adult frogs spend most Of their time
In the water, but they must come to
the surface to breathe. Toads once
they leave the water do not return to
it.-New York World.