Seasonal spermatogenetic cycle in the testis of Rana temporaria L., with special regard of the residual spermatogonia
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概要
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The seasonal spermatogenetic cycle was observed in the testis of the grass-frog, Rana temporaria, collected through the year in the vicinity of Sapporo, Hokkaido. Breeding occurs during from late March to the middle of April. During season, all spermatozoa are eliminated from the seminal tubules. The multiplication of the residual spermatogonia begins in early May and becomes active during June. Primary spermatocytes and the first maturation division appear from late June to July. The second maturation division and spermioteleosis continue through late June and August. Spermioteleosis is practically completed by the end of September or early October. No evidence of spermatogenesis during the winter period is observed.There are a certain number of residual spermatogonia retained in a state of rest with polymorphic nuclei lying in close contact to the inner wall of every seminal tubule. They are clearly distinguishable from the tissue cells by their conspicuous apperance in both size and structure. They persist always as primordial spermatogonia. After the discharge of spermatozoa in the breeding season, the residual spermatogonia repeat active divisions and start the new spermatogenetic cycle in preparation for the coming season.
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