Fig. 1. The bls mutation causes severe embryonic anemia that recovers in the larval stage. Wild-type and bls embryos stained with o-dianisidine, which detects cells containing hemoglobin. All embryos in this and subsequent figures are shown in lateral views, oriented with anterior and dorsal towards left and top of the page, respectively, unless otherwise specified. Blood cells pool in the Duct of Cuvier of wild-type embryos (arrowhead) at 36 hpf, but are absent in bls mutants. However, as the bloodless embryos develop beyond 5 dpf, blood cells begin to accumulate. By 7.5 dpf, blood cells can be detected near wild-type levels in the bls mutants, as they circulate through the heart and branchial vessels (arrowhead).