(A) During the first day of development, both neural crest cells (green) and placode cells (blue) form around the edges of the developing nervous system. (B) By the end of the first day, the placode cells have converged to form the olfactory placodes and the lens of each eye. (Other derivatives of placode cells are not shown.) Neural crest cells now surround the placodes. (C) By the third day of development, the olfactory vesicle has formed, and sensory neurons project into the olfactory bulb. Previously it was thought that all sensory neurons and their supporting glia derived from the placode (left). However, Saxena and colleagues now show that many (but not all) of the microvillous neurons derive from neural crest cells (right). Supporting olfactory ensheathing glia (OEG) cells might also derive from neural crest cells, but this has not yet been shown for fish.