Paraffin sections of whole-mount embryos in Figure 6 showing the location of FGF-8 message in pharyngeal arch 3. (a and c) Sham-operated embryos at stages 14 (a) and 18 (c). (b and d) Neural crest–ablated embryos at stages 14 (b) and 18 (d). (a) FGF-8 message is expressed strongly in the ectoderm covering the arch and weakly in the pharyngeal endoderm. (b) A similar pattern and level of expression of FGF-8 message after neural crest ablation to that of the sham-operated control. (c) Dramatic decrease in FGF-8 message expression at stage 18 in both the endoderm and ectoderm of a sham-operated embryo. (d) A similar decrease in expression in a neural crest–ablated embryo.