Fig. 8. The role of Nodal and Delta2 during secondary notochord induction in Ciona embryos. The positions of blastomeres that are discussed in the text are indicated. Ci-Nodal signals are indicated by red arrows and Ci-Delta2 signals by green arrows. For each schematic drawing, the expression pattern of the gene indicated above it is shown by grey coloured blastomeres. Schematic drawings are vegetal pole views of an early 32-cell stage embryo, a 64-cell stage embryo and a 110-cell stage embryo, from left to right. Although Ci-Nodal expression is not detected until the late 32-cell stage, an early 32-cell stage embryo is shown so that the b6.5 blastomere can be seen on the vegetal pole view of the embryo (compare with Fig. 3B). The roles played by Ci-Nodal and Ci-Delta2 signals during secondary notochord induction during these stages is indicated below the drawings.