The history of the germ cells of cottus bairdii girard

The primordial germ cells are derived from entodermal giant cells which are found first before the gut is formed and later along the ventral and lateral margins of the gut. Some of these cells pass through the lateral mesoderm to a position dorsal to the gut, where they are distinctly recognizable as germ cells. They are then shifted to the gonad region. Sex could be distinguished first at fifty‐two days. The female sex is indicated by early maturation stages and the beginning of the oviducal groove. The male sex is distinguished by the presence of the sperm duct. No tendency toward juvenile hermaphroditism is apparent. A portion of the oocytes formed during the first season matures for the first spawning, which takes place at the age of two years. The remainder form a reserve supply, which is increased each year by oocytes formed from dormant oogonia. Maturation in the male begins in September and continues until spawning‐time in April. Spermatogonia lying dormant within the cysts during maturation give rise to the sperm of the next season. ‘Spermatid masses,’ probably formed by the fusion of spermatids, are found in the cysts with the ripening sperm. Definitive sex cells in both sexes have their origin only in primordial germ cells. No transition from somatic cells to germ cells was found at any stage.