Fig. 7. Spatial expression of foxa determined by WMISH. A and C–F are lateral views with the vegetal (posterior) pole toward the bottom. (A and B) Hatched blastula. (B) View from vegetal pole to show that expression is in a torus-like pattern around the pole that does not include the central (mesodermal) region of the vegetal plate. (C) Early gastrula showing that expression is still confined to the blastopore. (D) Midgastrula, expression is now also found within the posterior archenteron. (E) Late gastrula, expression is found along the entire endodermal archenteron but is most intense in the foregut and hindgut. Open arrowheads show the top of archenteron that will develop into the mesodermal coelomic pouches, where foxa is not expressed. Expression is also detected within the oral ectoderm (arrow). (F) Early bipinnaria larva (80 h), viewed from the oral side. Staining is found within the foregut (filled arrow) and hindgut (open arrow). Staining is also apparent in the oral ectoderm at this stage but is not in the plane of focus in this view. Times indicated at the bottom on the right are hours after fertilization.