Avian primordial germ cells (PGCs) show a unique migration pathway during early development. As soon as the blood vessels have formed, PGCs enter the circulatory system, and migrate to the gonadal primordium. We measured the concentration and the size of PGCs and erythrocytes from the wild-type plumage and the sex-linked brown strains of Japanese quail embryos when PGCs are in circulation at Hamburger and Hamiltons stages 13-19. PGCs were high in concentration and large in size at stage 13, and

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... it showed a significant decrease as the function of embryonic development. Erythrocytes showed a low concentration at stage 13 and a significant increase as the function of embryonic development but the size was constant during stages 13-19. No strain difference was observed in these characters between the two strains of quail embryos.