The vast majority of invertebrates, most fish, reptiles and amphibians and all birds are oviparous, that is, they lay eggs with little or no embryonic development taking place within the mother. In aquatic organisms, fertilization is nearly always external with sperm and eggs being liberated into the water (an exception is sharks and rays, which have internal fertilization[15]). Millions of eggs may be produced with no further parental involvement, in the expectation that a small number may survive to become mature individuals.