developmental stage Medaka stage 0 OlatDv:0000020 Zoological Science 11: 825-839 (1994) - Stage 0 Unfertilized eggs: The mature unfertilized egg is an oblate spheroid measuring average 1,245.9 +/-3.9 um (n=122) in horizontal diameter and a little less (average 1,169.9 +/- 4.0 um, n=122) in vertical diameter. The egg proper is closely surrounded by a thick egg envelope, the chorion. The perivitelline space between the chorion and the vitellus is very difficult to recognize using a light microscope. The micropyle located in the chorion at the animal pole is a small trumpet- or funnel-like structure. A number of short villi (non-attaching filaments; average 200.3 +/- 4.7 / egg, n=38) are distributed over the whole surface of the chorion. At spawning, eggs are held together in clumps by a tuft of long attaching filaments (average 29.6 +/- 1.3 / egg, n=38) on the chorion surface in the vegetal pole area of each egg [13]. A large, transparent yolk sphere is located in the center of each unfertilized egg. The cortical alveoli (vesicles, ca. 0.4-45 um in diameter) and oil droplets are embedded at random in the cortical cytoplasm. The cortical alveoli contain a transparent colloidal material and usually one or sometimes a few spherical bodies [16]. The size of the oil droplets usually varies according to differences in the temperature during and after oocyte maturation, in the time after ovulation and among the individual females. - medaka_ontology unfertilized eggs