Abstract
This research was begun in 1929, and a preliminary account of some of the results of the investigation was published in theJournal of Anatomy, January 1932. It was initiated by the discovery, during experiments on intravitam staining in the guinea-pig, that dye-bearing cells collected in large numbers in the endometrium of the uterus and that their incidence there was cyclic. The first results were obtained in animals injected immediately after parturition and killed at intervals thereafter. In a short series of virgin animals, the series being established by determining the date of heat by the vaginal smear method (Stockard and Papanicolaou, 1917, 1919), practically identical results were obtained.