Morphology of and embryonic inversion in <i>V</i>. <i>globator</i>.

<p>(a) Adult spheroid with somatic cells and one embryo labelled. Scale bar: 50 μm. (b) Schematic drawing of <i>V</i>. <i>globator</i> parent spheroid with embryos. (c) Schematic drawing of <i>Volvox</i> embryo before inversion, with anterior and posterior poles and phialopore labelled. Cells are teardrop-shaped (labelled ‘T’). (d) <i>Volvox</i> invagination: the formation of wedge-shaped cells (labelled ‘W’) in the bend region initiates inversion. At the same time, cells in the posterior become spindle-shaped (labelled ‘S’), while cells close to the anterior fold (the region of increased positive curvature next to the bend region marked in the figure) become disc-shaped (labelled ‘D’). (e) At the end of posterior inversion, cells in the whole of the anterior hemisphere are disc-shaped, while cells in the bend region are pencil-shaped (labelled ‘P’). (f) As the anterior hemisphere peels over the inverted posterior, more and more cells become pencil-shaped. Red lines in panels c–f mark position of CBs. <i>Panel a adapted from [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2005536#pbio.2005536.ref043" target="_blank">43</a>] and panels c–f adapted from [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2005536#pbio.2005536.ref044" target="_blank">44</a>].</i> CB, cytoplasmic bridge; ECM, extracellular matrix.