A factor or factors which will stimulate the "letdown" of milk in the sow are present in the posterior pituitary gland of representatives of the 3 divisions of mammals, monotrernes (echidna), marsupials (the Wallaroo and the Austrahan phalanger, Trichosurus vulpecula) and placentals (rabbit, rat, cow, sheep, sow). The pituitary of a marlin or swordfish also caused milk "let-down" in a sow.