ウナギの生殖腺の成熟に関する研究-I : 性分化および生殖腺の成熟過程

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The processes of sex differentiation and sexual maturation of the eel, Anguilla japonica, were examined. In glass eels, the primordial germ cells standing in a line are found in each of the gonads (Pl. I, Fig. 1). The cells gradually increase in number under about 15cm in total length of the bodies, and steadily increase at 18cm or thereabout (Pl. 1, Fig. 2). The sex may differentiate at this stage, and histological structures of gonads become characteristic in both sexes, while ovaries and testes hardly be distinguished by means of their external appearance until the eels come to about 30cm in total length (Pl. I, Fig. 3 and 4). As they grow longer than some 30cm, the discriminative features of ovaries and testes become appreciable. In view of the observations described above, it is suggested that there is neither “phase of precocious feminization” nor “phase of juvenile hermaphroditism” in A. japonica. In testes of eels less than about 40cm, there may be seen many spermatogonia but no spermatocyte (Pl. I, Fig. 5), and the former gradually increase in number accompanying with body growth (Pl. I, Fig. 6). In silver eels having catadromous nature, a number of spermatocytes are found in testes, but spermatids scarcely ever (Pl. II, Fig. 1). In ovaries of eels ranging in total length from 25cm to 40cm, oogonia and primary oocytes are found intermingling (Pl. II, Fig. 3 and 4). As they grow over about 40cm, oocytes increase fast. In catadromous female fish, the cells develop up to the yolk vesicle stage (Pl. II, Fig, 5). It is generally found that the gonadal maturation of eels advance mostly in autumn and somewhat degenerate in winter, though the seasonal fluctuation in maturation are not so obvious.

ウナギの生殖腺の成熟に関する研究-I : 性分化および生殖腺の成熟過程

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