The Harderian gland of the northern grasshopper mouse, Onychomys leucogaster

The Harderian gland of the northern grasshopper mouse, Onychomys leucogaster, consists of glandular tubuloalveolar endpieces with secretory cells (small- and large-droplet cells) surrounding a wide lumen. Lumina from adjacent endpieces join repeatedly, forming progressively wider channels. Ultimately, a single secretory duct opens at the anterior canthus of the eye. Abundant sudanophilic materials secreted into the lumina of the tubuloalveoli drain into the orbit of the eye. The presence of amber–brown concretions in, and the intense fluorescence of, the Harderian gland suggest that in O. leucogaster the secretory materials also include porphyrins. Fluorescence of these secretions demonstrates that they drain from the orbit into the nasal passages; grooming spreads these materials from the nares onto other parts of the body. Although the Harderian gland of O. leucogaster shows no sexual dimorphism, there are age-related changes. Small-droplet cells are present at 1 week of age and large-droplet cells appear by 2 weeks. By 4 weeks the gland is comparable to that of adults. Glands of a few adults exhibit two features rarely reported in other rodents: (1) clusters of degenerated tubules characterized by a loss of the secretory epithelium and (2) large aggregations of lymphoid cells.