Dark macroscopic pigmented areas were present in the uterus of the Arctic Fox.
The pigment was intracellular and granular, and was concentrated in the basal layer of the endometrium. It was found to consist of haemosiderin together with a lipid component. The pigmented areas, former placental sites, remained in some cases up to ten months after parturition.
It is suggested that the number of pigmented areas gives a measure of the number of implantations present during the previous season.