Efferent ductules of the boar--a morphological study.

The efferent ductules of the boar were investigated by means of corrosion casts, light microscopy, scanning and transmission electron microscopy. They arise from an extratesticular rete and constitute the major, caudolateral part of the ascending limb of the caput epididymidis. Ductules may be subdivided into three segments: a slightly undulating testicular segment, a highly coiled intermediate segment and a moderately coiled epididymal segment. A decrease in diameter is particularly marked from the intermediate to the epididymal segment. The epithelial transitions from the extratesticular rete to the efferent ductules and from these to the epididymal duct are clearly demarcated. The epithelium of the efferent ducts consists of principal and ciliated cells. Mononuclear leukocytes are found in the basal half. Ultrastructural evidence supports a strong absorptive activity of principal cells. Apical protrusions are not considered to be a proof of apocrine secretion but rather seem to be artifacts. The nature of membrane-bound granules of variable density remains speculative.