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Masato Hasumi, Hisaaki Iwasawa, Yoshitaka Nagahama, Seasonal Dynamics of Reproductive Organs in Male Salamanders of the Species Hynobius nigrescens, Copeia, Vol. 1990, No. 2 (Jun. 27, 1990), pp. 367-377
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Hasumi et al. (1990) studied this question.
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