Water-Tight


The ability to stop water from entering or leaving.  Water-tight eggs keep in moisture so that the eggs do not dry out.  This allows the eggs to be laid on land instead of in water.  Water-tight skin (like ours) also keeps in most moisture, but an amphibian's skin is not water-tight, so it must spend time in a moist environment.


Fish and Robin Eggs
Fish eggs, on the left, must be laid in water. Robin eggs (on the right) are water-tight, so robins can lay them in their nests.