Epididymal maturation of spermatozoa in the marsupial Trichosurus vulpecula : Changes in motility and gross morphology

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Abstract
Epididymides from mature T. vulpecula were divided into five regions: the proximal and distal caput (1, 2), the proximal and distal corpus (3, 4) and the cauda (5). Sperm suspensions prepared from these regions had means of 1, 10, 31, 58 and 75% motile forms respectively. Vigour of movement also increased correspondingly, with the development of active forward progression by regions 4 and 5. The mean percentages of morphologically mature spermatozoa in the five descending regions were, respectively, 0, 0, 6, 52 and 82. Three distinct stages in morphological maturation could be recognized, with the bulk of sperm population successively moving through these stages in regions 1, 2 and 3. Maturation involves pivoting of the nucleus on the flagellum from perpendicular to parallel, contraction of the cytoplasmic droplet and migration onto the mid-piece, and contraction of the acrosome from a prominent, voluminous, hoodlike structure on the dorsal surface of the nucleus. These changes are discussed in the light of preliminary ultrastructural observations.