A Frog's Life: Metamorphosis page 2

3. This mass of soft, jelly-coated eggs, often numbering in the hundreds or thousands, often sticks to water plants or other vegetation. The eggs hatch into tiny fish-like tadpoles that have gills, like fish, to allow them to breathe while in the water.

Illustrated cell division in an egg:
(illustrated at left, from left to right, top to bottom)

1) The fertilized egg at the single cell stage.

2) Within an hour or two after being laid, the first cleavage (cell division) occurs. The one cell is separated into two embryo cells. It's thought that these two cells become the right and left sides of the tadpole.

3) Cleavage continues, with the two cells splitting into four.

4) And the four cells into eight (not pictured) and then 16. The embryo at the 16-cell stage is called the "morula" and looks somewhat like a raspberry.

5) More cell division occurs. At this stage, the embryo is called the "blastula."

6) At about 100 hours, the tadpole begins to take shape.

7) The tadpole's features are more discernible. The tail begins to move from side to side.

8) Tadpole hatching.

9) Soft, jelly-coated frog eggs.