Cyclical Reproductive Changes in the Non‐ciliated Epithelia of the Epididymis of Birds

The epididymis of two species of domestic birds, the domestic fowl ( Gallus domesticus ), duck ( Anas platyrhynchos ), and of domestic and feral guinea‐fowl ( Numida meleagris ) was studied during the three main phases of the reproductive cycle (prepuberal, sexually mature and active, and sexually mature but inactive or resting) with a view to identifying major histological and ultrastructural changes associated with and distinctive for each phase. Rete testis cells accumulated numerous variably sized lipid droplets in all birds, as well as large heterogeneous and lipofuscin‐containing dense bodies in the guinea‐fowl, during the resting but not in the other phases. The principal or Type III cells of the connecting and epididymal ducts exhibited profound structural changes, including, but not limited to, rarefied cytoplasm, inconspicuous and general loss of sparsely granular endoplasmic reticulum, loss of secretory vesicles in the drake, and an enhanced and conspicuous presence of lipid droplets in the guinea‐fowl. The rete cells appeared to be less sensitive than the Type III cells to a reduced level or absence of lumenal androgens. These phase‐dependent changes may help to prevent or minimize discrepancies in the interpretation of the normal structure of the epididymis in birds during the sexually active phase, as distinct from the other two phases and their intermediate phases.