The micromorphology of the intratesticular duct system has been investigat ed with emphasis on the effect of the seasonal variations. The period between September and April was considered as the active period and that between May and August as the inactive one. The active period was characterized by regional differentiation of the duct system which compris
the terminal portion ed: 1) initial segment, which was delineated from of the seminiferous tubule by a sphincter-like constriction. This segment
reduced spermatogenic was subdivided into; transitional zone lined with
modified Sertoli cells and finally epithelium, intermediate zone lined with
a terminal zone representing an epithelial dilatation, 2) tubulus rectus, which was not always straight and lined with cuboidal epithelium and some lymphocytes and macrophages, 3) rete tubules, which were highly branched and anastomosed epithelial chambers lined with "3" types of cells. In some animals the chambers got fused forming a huge labyrinthine cham ber designated as mediastinal labyrinth. The boundary tissue sufrounding the epithelial elements was easily demarcated from the loose interstitial tissue. The inactive period showed the following changes: a) attenuation of the epithelial lining of the different segments, b) high reduction in the luminal content of the sperms, degenerating sperm components and luminal macrophages, c) diminution of the size of the rete tubules which became separated with wide interstitial spaces made up of homogeneous dense fibrous tissue, d) the boundary tissue could not be demarcated from the interstitial tissue.