卵胎生有肺類ナミコギセルガイの雌雄同体現象の研究 III : 生殖細胞の発達

概要

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In the ovoviviparous snail, Euphaedusa tau, the development of germ cells in the ovotestis was studied histologically in relation to the reproductive cycle. Stages of growth of the snail were indicated by the number of shell whorls. The snail is born with the shell of three whorls, that is, at Stage 3. When it grows up to Stage 4, the ovotestis becomes identified in a form of a mass of gonial cells, in which a small number of previtellogenic oocytes can be seen. However, oocyte maturation does not accomplish until the snail develops to Stage 10, the full-grown stage. Spermatogonia increase in number at Stages 5 and 6. Spermatogenesis occurs in some snails at Stages 7 and 8. When the snail grows up to Stage 9, the ovotestis is full of spermatozoa. During late autumn and winter, the male system seems to be functional in the ovotestes of the snails at Stages 9 and 10. In spring, spermatozoa are released to pass along the hermaphroditic duct. The oocytes maturate sequentially and reach about 50μm in diameter. Thereafter, ovulation occurs. It continues for a long time by sending out mature oocytes one by one into the hermaphroditic duct. The acini of the ovotestis which have discharged spermatozoa and oocytes are empty for a while, though gonial cells and perhaps nurse cells remain in periphery. Spermatogenesis occurs again. Some of the ovotestis from aged snails show the degenerating figures.
1982-10-31