Figure 4. Segmentation of Abatus cordatus. (A) Section through a cleaved egg showing blastomeres and the remaining yolk mass at the vegetal pole (11 days after fertilization). (B) SEM view of a completely cleaved egg (14 days after fertilization). Blastomeres are visible where the fertilization membrane is destroyed (white arrow). Black arrow shows a furrow. (C) Section through a cleaved egg at the end of the segmentation (15 days after fertilization). Black arrows show the large intercellular spaces that communicate with the perivitelline space at the level of the furrows. (D) Light micrograph of a wrinkled stereoblastula (26 days after fertilization). Arrows show furrows. A and C are semi-thin plastic sections (toluidine blue, pH 11.5). Abbreviations: ap, animal pole; bl, blastomere; em, embryo; fm, fertilization membrane; N, nuclear area;