Morphological characteristics of cells with apical nuclei in the initial segment of the adult rat epididymis.

The cytology of epithelial cells with apical nuclei in the initial segment of the rat epididymis was studied with the light and electron microscopes. Two types of cells were distinguished and were designated apical cells and narrow cells. The apical cells are more numerous than the narrow cells and closely resemble principal cells except for the location of the nucleus. They probably correspond to the apical cells of Reid and Cleland ('57) and may represent a variation of the principal cell. The narrow cells differ markedly from the apical cells in both light microscopic appearance and fine structure. Narrow cells strain intensely with toluidine blue and are characterized by a slender shape, many mitochodria with tubular cristae, and a large number of apical cup-shaped cytoplasmic vesicles. The possible relationship of narrow cells to other cell types is discussed.