Why is the number of eggs, laid by frogs at a time, much higher than those laid by a hen?
In frog, external fertilisation takes place and frog lays eggs in water, where eggs are exposed to predators and water current. Most of the eggs of a frog are destroyed by the time and tadpoles come out of some of them. Thus, to increase the chances of fusion of gametes, the frog releases a lot of eggs. But a hen lays eggs on land and takes care of them during incubation. Hence, a frog needs to lay thousands of eggs. This is not the case with a hen.