Fig. 12. Archenteron inflation by fluid transfer from the blastocoel. (A-D) Cavities between the blastocoel and the archenteron were visualized with SIM (sagittal section, A), in cleaved embryos (B), and with MRI (sagittal section of intact embryo, C). (D) Sagittal view of the SIM dataset from A rendered to visualize internal spaces, highlighting (red arrowheads) the cavities connecting the blastocoel and archenteron. (E) Transverse volume render of the SIM dataset from A. Cavities are highlighted in red in the tracings shown in d' and e'. An animation of this volume rendering is presented in Movie 8 in supplementary material.