SPIRAL PATTERNS IN THE MICROPYLAR WALL AND FILAMENTS ON THE CHORION IN EGGS OF THE MEDAKA, ORYZIAS-LATIPES

The relationship between spiral patterns in the inner wall of the micr opyle and attaching and non-attaching filaments on the chorion was inv estigated by electron microscopy in eggs of the medaka, Oryzias latipe s. There were both right- and left-handed spiral patterns of attaching filaments that arose from the chorion at the vegetal pole area. In th e majority of eggs examined, however, the prominent folds in the inner wall of the micropylar vestibule descended toward the micropylar cana l in a left-handed spiral. This spiral pattern in the micropyle may re flect surface indentations in the cytoplasmic extension of the micropy lar cell during formation of the micropyle apparatus. The present obse rvations suggest that the patterns of these spiral structures of the c horion are caused by the rotation of the oocyte due to the movement of follicular cells during oogenesis. (C) 1993 Wiley-Liss, Inc.