Hemoglobin expression during early development. (A-H) Expression at HH10 of α^π (A), α^A (B), ρ (C), and ϵ (D) globin transcripts and sections through indicated level of α^π (E), α^A (F), ρ (G), and ϵ (H). (I-W) Expression of ρ at HH5 (I), 7 (J), 8 (K), 10 (L), and 12 (M). Sections of HH7 (N-P) and HH8 (Q-S) embryos are shown as indicated. Arrows point to cells initiating expression within a BI. Representative BI morphology is shown for HH9 (T), 10 (U), 11 (V), and 12 (W).