"Frogs tend to lay many many eggs because there are many hazards between fertalization and full grown frogness! Those eggs that die tend to turn white or opaque. The lucky ones that actually manage to hatch still start out on a journey of many perils.
Life starts right as the central yolk splits in two. It then divides into four, then eight, etc.- until it looks a bit like a rasberry inside a jello cup. Soon, the embryo starts to look more and more like a tadpole, getting longer and moving about in it's egg.
Usually, about 6-21 days (average!) after being fertilized, the egg will hatch. Most eggs are found in calm or static waters, to prevent getting too rumbled about in infancy!
Some frogs, like the Coast foam-nest treefrog, actually mate in treebranches overlooking static bonds and streams. Their egg masses form large cocoon-like foamy masses. The foam sometimes cakes dry in the sun, protecting the inside moisture. When the rain comes along, after developement of 7 to 9 days, the foam drips down, dropping tiny tadpoles into the river or pond below."