Embryos during cleavage and blastula stages. (A) zygote stage (0 h); (B) early 1-cell stage (0.25 h); (C) late 1-cell stage (1.5 h); (D) 2-cell stage (1.75 h); (E) 4-cell stage (2.5 h); (F) 8-cell stage (3 h); (G) 16-cell stage (3.5 h); (H) 32-cell stage (4 h); (I) 64-cell stage (4.5 h). Schemes illustrate the position of cells and cleavage planes from a top-down view (D-H). Abbreviations: ap, animal pole; bm, blastomeres; ch, chorion; cp(s), cleavage plane(s); ft, filament tuft; mi, micropyle; ml, mucous layer; ps, perivitelline space; vp, vegetal pole; y, yolk. Scale bar = 500 μm.