Once eggs are released and fertilized, a horny shell or membrane is secreted around each one as they pass through the oviducal gland or shell gland . Some sharks produce a shell that is tough and can protect the young. In other species the membrane is slight or vestigial and the young develop and hatch within the uterus of the female. The eggs and egg cases produced by different species are highly variable. Eggs can be up to 60 or 70 mm in diameter and encased in shells up to 300 mm long.
Shapes vary from spindle to purse-like with tendrils and hooks.
During copulation sharks meet face to face. As seen in this picture the male inserts one of his claspers into the cloaca of the female. Sperm contained within sperm packets called spermatophores are delivered to the female via a groove in the clasper. The spermatophores are forcefully ejected by contracting organs known as siphon sacs which use seawater currents to carry the spermatophores Photo modified from Sharks , Editor John D. Stevens. Another marked difference between the male and female sharks of some species is the thickness of their skin.