Fluctuations in serum calcium in doves and chickens have been associated with egg shell formation or ovarian activity (1, 2). In doves the serum calcium rises during the follicular phase of the ovarian cycle (3). In the hen it has been correlated with the size of the egg (4). However, it was not until 1936 that estrogens were demonstrated to cause a rise in blood calcium (5). Kyes and Potter (6) noted that many female pigeons have solid bones, while males uniformly have marrow-filled bones. The condition of the bones was correlated with the size of the ovarian follicles. When the follicles were 2 mm. or less in diameter, the femurs contained large marrow spaces. Osseous tissue partially invaded the marrow in birds in which the follicles were more than 4.5 mm. in diameter, and bony spicules filled the marrow cavities when the follicles were 10.0 mm. or larger in diameter. The present investigation