Abstract
In lower vertebrates, the bone-mineralizing hormone "calcitonin" is secreted from ultimobranchial glands, which assume various shapes, e. g., follicles, cellular masses, or cell strands. Histological observations support the view that in some teleosts, the glands increase in size when females maturate. We determined the exact volume of the gland in juveniles and adult males and females of a teleost, Ryukyuayu (Plecoglossus altivelis ryukyuensis). Furthermore, we examined plasma Ca, Na and K levels. In this species, the gland was fundamentally composed of a single follicle. The gland volume was converted to numerical data under a certain condition. It thus became clear that the value of the follicle wall was significantly increased only in maturing and mature females with high plasma Ca levels and that the value of the lumen did not show any statistically significant changes during growth and maturation.
