Fig. 2

Summary of the development of pleuropodia in S. gregaria embryos. (a) Scheme of S. gregaria embryogenesis marking key developmental events in the embryos and timing of the two experiments on pleuropodia. Numbers above the scale are days from egg-laying, numbers below the scale are percent of embryonic developmental time. Yellow boxes indicate the stages that were sampled for RNA-seq. Eggs with the developing embryos at each stage are shown below the scale, insets for the 4–8 day stages show the embryo dissected out from the egg. (b) External features of the developing pleuropodia; after hatching part of the stretched exuvia is shown; the degenerated pleuropodium is marked with an arrow. (c) Paraffin sections through the pleuropodium and surrounding tissue. Pleuropodia are marked with arrowheads. Anti-Phospho-Histone H3 antibody (green) detects cell divisions in the immature glandular cells (tip of appendage bud) on day 4 and 5, not in later stages. The pleuropodial stalk cells, haemocytes entering the pleuropodia and cells in other tissues were labeled. Nuclei (grey) enlarge from day 6. The text below the pictures refers to the main events in the glandular cells. EX, exuvia; L, larva. Scale bars: in (a) (eggs), 1 mm; in (b), 0.2 mm. Background was cleaned in photos in (a) (see Methods)