Cellular junctions of the lining epithelium of the efferent ductules of the mouse, guinea pig, and human testes were examined by freeze-fracture. A belt-like gap juncion consists of a large aggregation of particles with a few fragments of the tight junctional strands and circumferentially occupies the adluminal area between the nonciliated cells. This type of gap junction appears to be one of the components of the junctional complexes in mammalian efferent ductules. Functional significance of

more »

... e belt-like gap junction is discussed in the light of the findings. Regional differences of the tight junctions of the lining epithelium along the excurrent duct of the rat testis was reported in our previous paper (SUZUKI and NAGANO, 1978) . In that paper, the junctions of the ductuli efferentes showed a characteristic feature. The tight junctional strands or grooves were minimum in number along the duct and sometimes were absent in the junctional area. Furthermore, a beltlike gap junction was present circumferentially in the apical part of the cytoplasm between the non-ciliated cells. Fine structural studies on the ductuli efferentes have been made in several mammals by thin sectioning (LADMAN and YOUNG, 1958; MORITA, 1966; LADMAN, The purpose of the present paper is to describe that the belt-like gap junctions occur in the ductuli efferentes in some mammals other than the rat. MATERIALS AND METHODS Testes with epididymides of the mouse, guinea pig and human were used in this study. The human materials were obtained by castration from two patients with prostatic cancer, aged 71 and 84, who had never received hormonal treatment. These materials were fixed by vascular perfusion through either the aorta or the testicular artery. The fixative consisted of 2.5% glutaraldehyde and 1% formaldehyde from paraformaldehyde in 0.1M cacodylate buffer. After completion of the perfusion, efferent ductules were dissected out in the fixative under the dissecting microscope. Segments of the ductules were treated with buffered 30% glycerol for 3hrs and 185