A shark's eggs become fertilized in the female shark's body. The male shark passes sperm through extensions of the pelvic fins to fertilize the eggs and the gestation period can last up to two years.
The three different kinds of shark egg development are viviparity, oviparity and aplacental viviparity. Viviparity is a process where the eggs hatch in the female's body and a placenta feeds the babies. The placenta's role is to provide oxygen and nutrients from the female shark's bloodstream. Lemon sharks, bull sharks, whitetip reef sharks, blue sharks and hammerheads are some of the sharks that are viviparous.
Sharks who give birth through oviparity release eggs in the ocean that will hatch at a later time. The eggs aren't watched by the parents and are often eaten by predators. The shape of the eggs is similar to a pouch and some have tendrils that join the egg to objects. Zebra sharks, swellsharks, catsharks and hornsharks and certain epaulette sharks are oviparous.
Great white sharks, nurse sharks, tiger sharks, pygmy sharks, soupfin sharks, sand tiger sharks, crocodile sharks and sawsharks reproduce through aplacental vivparity. This method entails eggs hatching and the babies developing in the female's body. However, there is no placenta to nourish the newborn pups.