In the region anterior to the kidneys, the oviducts form small expansions, the shell glands, whose secretion forms the shell of the egg.

Shell glands are small extensions of the posterior parts of the oviducts of sharks. In sexually mature fish, shell glands reach considerable size, their glandular walls secrete a secret that transforms into a dense horn-like shell with growths and flagella, which protects the egg and the developing embryo.