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Stage 0 (0 min)Unfertilized eggs
Drown by T. Iwamatsu
(Abbr. at : attaching filament, ca : cortical alveolus, ch : chorion, mp : micropyle, od : oil droplet)
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.
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. The size of the oil droplets usually varies accordingto differences in the temperature during and after oocyte maturation, in the time after ovulation and among the individual females.