There are marked sex differences in the Harderian gland of the C3H/He mouse strain, the females having a larger number of mast cells than the males as one of the major differences. Mast cell counts of the Harderian gland were made on male mice subjected to combinations of adrenalectomy, gonadectomy and administration of sex steroid hormones. Castration alone caused a significant increase in the count resulting in about three times the number found in intact males. Castration plus adrenalectomy increased the count over 6-fold, to levels close to those found in female mice. Administration of testosterone or estrone to the mice which had been castrated and adrenalectomized prevented the increase, while progesterone treatment had no effect on the count. Although the number of mast cells in the male Harderian gland was necessarily small compared to either the female gland or that of castrated and adrenalectomized males, no obvious dimorphism could be found microscopically.

The effects of lighting conditions and/or gonadal secretions on the porphyrins of rat Harderian glands were studied. In female rats, exposure to constant light (= LL) induced a 50% decrease of porphyrin in the Harderian gland. Ovariectomy in these animals caused an increase to levels comparable to those found in intact controls. In males, exposure to constant darkness (= DD) produced a marked increase in the glandular porphyrins together with greatly decreased weights of accessory sexual organs. Further, orchidectomy remarkably increased porphyrin levels in rats kept under conditions of LL or DD. Administration of testosterone propionate to castrated male rats significantly decreased the porphyrin contents in the gland, although estradiol benzoate and progesterone treatments had no effect on the levels. Similar results were obtained in female rats.

The presence of dendritic cells containing melanin granules has been demonstrated employing silver impregnation and electron microscopy in the interstitial tissue of the Harderian gland of the mouse.Two types of melanocytes either with or without the various developmental stages of melanin granules were found in the gland. Cells with developing granules were more dendritic and contained a largenumber of cytoplasmic organelles.The other cells were ellipsoidal or slender in shape and contained few cytoplasmic organelles and a large number of fully melanized granules but no developing granules. In general the granules of the Harderian gland melanocytes resembled granules from other organs (particularly the skin of the eyelids).The general size range of the granules was 0.2–0.9 µm. Each granule was enclosed by a membrane.The Harderian gland macrophages contained fully pigmented melanin granules of various sizes. The granules were enclosed by a membrane either singly or in groups. Some of the melanin granules within the phagosomes showed signs of degradation, revealing the underlying matrix.