Frog, Toad and Salamander Eggs
Nature Bulletin No. 600-A April 17, 1976
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
FROG, TOAD AND SALAMANDER EGGS
The use of eggs in the celebration of Easter harks back to ancient pagan
rites in which the egg was a symbol of new life or resurrection. This
connection of eggs with magic and mysticism is understandable. An egg
doesn't cat and it doesn't move. To all outward appearances it just sits
there -- a thing. Then, suddenly, out of it comes an eating, breathing,
wriggling new creature.
Nature seems reluctant to expose to public view the life processes by
which the single cell of a fertilized egg changes into a many-celled
many-parted young animal. The microscopic eggs of mammals develop
inside the body of the mother. Birds' eggs with their large stores of yolk
are includes in opaque egg shells. So are those of turtles, lizards and
some snakes -- other snakes being born fully formed. The eggs of all
but a very few insects are also concealed in shells. The eggs spawned
by some fishes are translucent, but even in them it is rather difficult to
follow the changes. By far the best eggs for watching the development
of embryos are those of the amphibians -- frogs, toads and salamanders.
Their rather large eggs have only a transparent jelly covering. The
individual cells and organ rudiments are plainly visible under a hand
magnifier or microscope. Such eggs are easy to care for and observe in
late .March until June, in the Chicago region, the eggs of these
amphibians are not difficult to find in standing water. The tour common
kinds of Salamanders lay eggs first, often before the ponds are
completely free of ice. The large Tiger Salamander, for example,
attaches its egg clusters to submerged sticks or plants in woodland
pools. Each newly-laid 2-inch blob of jelly, containing about 50
one-eighth-inch eggs, later swells to twice this size. A half dozen or
more kinds of frogs breed here. Their eggs range from the tiny scattered
ones of the Cricket Frog and the Spring Peeper in early spring, to the
huge watery floating egg masses of the Bullfrog in early summer. In
April those of the Leopard Frog, with 3 to 5 thousand 1/16-inch eggs in
each mass, are most often used for study. The American Toad lays still
smaller eggs like a row of beads in long strings of jelly, usually many
yards in length.
To watch the development of an amphibian's egg under a microscope is
a fascinating drama -- with action in slow motion. Fortunately, the show
can be stopped at any point by putting them in a refrigerator at a little
above freezing. Later. brought back to room temperature, the show
picks up where it left off.
These eggs are all camouflaged -- darkly pigmented on the side that
floats uppermost and white on the underside, due to the yolk. A
newly-laid egg is a single cell. First a furrow forms on top and grows
down, dividing the cell into two. Then, a second furrow at right angles
to the first divides the egg into four quarters. Later cleavages give 8
cells, 16 cells and so on -- each division requiring about one hour. Soon
it is a plastic hollow ball of very small cells. Then comes a precise
sequence of folds, creases, tucks, dimples and elongations. Eyes, ears,
gills, a mouth, a tail, and a beating heart are formed. Soon it is a
twitching tadpole ready to be born.
I lease take only a few eggs. Leave the rest to grow up for more eggs in
years to come.
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Update: June 2012