Cranial placodes and sensory neural crest during head development in zebrafish. A schematic side view of the zebrafish embryonic head is shown (anterior is to the left and dorsal at the top). Approximate anatomical positions of the individual placodes are reconstructed from the in situ hybridizations taken from the ZFIN database . Panel A depicts the embryo during segmentation stages (11–24 hours post fertilization). Panel B depicts the embryo during the pharyngula stages (24 – 48 hours post fertilization). Distinct placodes are marked by different colors. Ganglia of mixed placodal and sensory neural crest origin are represented by circles where half of the circle is colored in gray (neural crest). The optic vesicle and the retina, which originate directly from the neural tissue, are in black.