Projections of confocal image stacks, showing the distribution of rhodaminated dextran (RD; green) injected within juvenile rudiments at various time points post-injection (PI), with DAPI (blue in A–C) or with RD alone (D–H).

<p>(<b>A</b>) Projection of three sections; larva fixed 10 min PI. Arrow points to vestibule labeling (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113866#pone-0113866-g002" target="_blank">Fig. 2B</a>): a thin layer of RD between the vestibular ectoderm and the floor of the vestibule surrounding a primary podium. (<b>B</b>) Projection of sixteen sections; larva fixed 24 hrs PI. (<b>C</b>) Projection of twenty-three sections; larva fixed 24 hrs PI. Arrows in B, C point to labeling in the lumen of primary podia, which is contiguous with the hydrocoel (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113866#pone-0113866-g002" target="_blank">Fig. 2C</a>). (<b>D</b>) Projection of thirty sections; larva fixed 24 hrs PI. Arrow points to punctate labeling of RD, which has accumulated in the right somatocoel. (<b>E</b>) Projection of twenty-four sections; larva fixed 5 min PI. Arrow points to the lumen of a developing spine. Note that in this common "vestibule" pattern, RD labeling surrounds every tube foot and spine element on the oral side of the rudiment. (<b>F</b>) Projection of thirteen sections; larva fixed 5 min PI. Arrow points to a thin layer of RD between vestibular ectoderm and the floor of the vestibule surrounding a primary podium; i.e., vestibule pattern. (<b>G</b>) Projection of 47 sections; larva fixed 10 min PI. Arrow points to RD accumulation in the lumen of a primary podium. (<b>H</b>) Higher magnification projection of nine sections; larva fixed 30 min PI. Arrow points to RD, which appears in a punctate pattern in a spine lumen. Larvae are all oriented approximately as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113866#pone-0113866-g002" target="_blank">Figure 2</a>, with the stomach (S) towards the left of each panel, and the rudiment towards the right. Scale bars: A = 100 µm; B = 166 µm; C, D = 133 µm; E−G = 110 µm; H = 63 µm.