Function of the rectal gland in the spiny dogfish.

The rectal gland of the spiny dogfish, Squalus acanthias, secretes a fluid which is essentially a sodium chloride solution with a concentration about twice that of the plasma and greater than that of sea water. Observed volumes of flow are sufficiently large to make it clear that the rectal gland can remove from the blood relatively large amounts of sodium chloride, and presumably this is its function.