There is no placental connection to the mother. Young are born after development is completed. Among the interesting variations in ovoviviparity is fetal cannibalism. Oophagy, in which young eat non-fertilized ova after using up their own yolk early in development, is also found in other lamnoid sharks, the makos and their kin. This is the most advanced mode of reproduction and is the type employed by most commercially important species.
Embryos initially grow using stored yolk.
Later a pseudo-placental connection is formed between the yolk sac and the uterine wall. Resulting embryos usually reach a quite large size at birth. Most sharks have independent gestation periods and ovarian cycles, that is, they do not begin egg development until after giving birth. Thus, including gestation, they give birth about every two years. Other species, such as hammerheads and sharpnose sharks, concurrently gestate and develop eggs, thus they can mate immediately after giving birth, producing yearly litters.