Ductuli efferentes of the bull-a morphological, experimental and developmental study.

The light and electron microscopic structure of efferent ductules (ED) has been investigated in the mature intact, treated, and immature bulls. On a morphological basis, ED could be subdivided in two major segments. The proximal segment (near rete tests) possesses greater tubular diameter and taller and taller epithelium. Tje epithelium of ED consists of ciliated and nonciliated cells and a smaller number of intraepithelial lymphocytes and macrophages. The nonciliated cells can be distinguished into three different types: type II is characterized by specific granules, type III by vacuoles, whereas type I lacks either granules or vacuoles. Type II and III probably represent two cell species, which differ from each other in their morphological and histochemical properties, while type I may be the "inactive" form of the II and III cells. Type I cells occur throughout ED but they prevail in the proximal region. Type II cells inhabit the proximal segment and type III cells populate and prevail in the distal segment. The structure of nonciliated cells indicates that, in addition to resorptive and carbonic anhydrase activities, they are engaged in marked secretory activity. The control and significance of such an activity is discussed. Developmentally, the difference in tubular diameter in the proximal and distal regions is expressed shortly after birth, the morphological features of resorption were established by 25 weeks, while the formation of granules and vacuoles were not observed until 35 and 50 weeks, respectively.