Structural changes in the overies, uterus and vagina of the Senegal galago (Galago senegalensis senegalensis) have been observed at several stages of the oestrus cycle in both wild and captive animals. These changes have been correlated with the periodic opening and closing of the vaginal orifice and changes in vaginal cytology. The general pattern of these structural changes was similar to that seen in other mammals but showed the following special features: periodic opening and closing of the vaginal orifice; a prolonged post‐ovulatory invasion of the uterus and vagina by large numbers of eosinophil leucocytes; an unusually long life of the corpus luteum of the nonpregnant cycle. Although this animal did not menstruate its endometrium appeared to have to dual arterial supply like that seen in those higher primates that do menstruate. The coiled, elastic endometrial arteries formed a vascular adaptation to permit rapid dilatation of the uterus during early pregnancy. The urethra perforated the whole length of the long and peniform clitoris and this was associated with the periodic opening and closing of the vaginal orifice. These features made sexing very difficult. The observed time of occurrence of oestrus, together with field data on pregnancy stages and times of birth, indicated the probable occurrence of two breeding seasons in the year separated by long periods of anoestrus. Twinning was found to be uncommo