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• W138454344 abstract "Sex differentiation and development of the gonad were examined histologically during larval, metamorphosing, and young adult stages in the Japanese river lamprey, Lampetra japonica, collected throughout the year in the Assabu River, southern Hokkaido. Gonads of all ammocoetes with total lengths below 30 mm were sexually indifferent. During the subsequent course of larval growth, gonial germ cells developed to form definite cysts in all of the gonads examined, revealing the occurrence of the cystic stage in initial sex differentiation of the lamprey. In all ammocoetes with total length of 70-90 mm, germ cells in the cysts more or less showed meiotic nuclear changes, though the degree of appearance of the premeiotic cysts varied in different specimens observed. Differentiation of ovaries with growing oocytes followed the cystic stage in some larvae of total length of 70-90 mm. Testicular differentiation was observed to occur either with the breakdown of germ cell cysts and rearrangement of surviving germ cells at the cystic stage or with extensive degeneration of growing oocytes and development of gonial germ cells preexisting at the ovarian phase. It was presumed that about 10 to 20% of defined males of the lamprey had passed the latter course of testicular differentiation. A nearly 1: 1 ratio of sexes seemed to be established in the lamprey exceeding 150 rom in total length. The appearance of vitellogenic oocytes and of spermatocytes was never observed even in metamorphosed, downstream migrants of the lamprey. Since the investigation of Okkelbergl ) on the brook lamprey, Entosphenus wilderi, several reports have been concerned with sex differentiation and development of the gonad in several species of lampreys. In these reports, much attention has been paid to the occurrence of a female or intersexual stage in early period of gonadal development: female and male germinal elements coexist together without any distinct localization in the somatic stroma of the gonad of essentially all juvenile animals. Some workers such as Okkelberg2) and Champy3) regarded this as a feature of sexual indetermination at an initial stage of gonadal development. However,. Hardisty4) brought forward the interpretation that it was nothing but a reflection of an innate tendency of germ cells to differentiate autonomously in the female direction in the gonad of which future sexes had already been determined. There is paucity of information about reproductive physiology of Japanese lampreys, and detailed reports on the process of gonadal development and maturation are lacking so far as the present writers know. In the present study, the * Laboratory of FreshWater Fish-OUlture, Faculty of Fisheries, Hokkaido University (~!:§~#1:*i¥:!lf:'IlB~*:lt~!lf:~§!)" @default.
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• W138454344 date "1982-11-01" @default.
• W138454344 modified "2023-09-23" @default.
• W138454344 title "Sex Differentiation and Development of the Gonad in the Japanese River Lamprey, Lampetra japonica" @default.
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