Figure 6. Embryonic development of the nematode C. elegans within the eggshell. (Left to right). 1. Pronuclei form after fertilization. 2. Prior to pronuclear fusion, spindle aligns perpendicular to long axis of the embryo. 3. Maternal and paternal chromosomes mix and the first mitotic division ensues. 4. AB cell (left) and P1 cell (right) are the result of the first  asymmetric division and will each give rise to different cell lineages. 5. Asynchronous second division wherein AB divides before P1. 6. Four-cell embryo showing ABa, ABp, P2 and EMS (bottom) cells. EMS cell will divide to give MS and E cells. 7. Morphogenesis initiates by movement of E cells towards the center of the embryo. 8. One and a half (1.5)-fold stage. 9. Well formed larva inside eggshell. Fertilization to hatching takes about 12 hours at 22 C.

Photograph courtesy Fabio Piano (Cornell University).
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