Fig. 1. Vital dye staining of the embryos. The embryos are viewed from the aboral (dorsal) side, with the animal side at the top. The left and right sides of the embryos correspond to those of the viewer. (A) An early gastrula H. pulcherrimus embryo stained with Nile Blue dye on the right side (arrow). The pressure of the glass needle has slightly indented the embryo along the midplane (arrowheads), through which the embryo is about to be dissected. (B) An H. pulcherrimus larva derived from the left half of an embryo that had been stained on the left side and dissected along the midplane in the early gastrula stage. The archenteron of the half larva is indicated by arrowheads. The staining is on the left side of the half larva (arrow). Scale bar: 100 µm.