Although the origin of the acoustic ganglion has been the subject of numerous studies there is no unanimity of opinion about it. Most of the earlier investigators (Bartelmez, 1922; Adelman, 1925), using mammalian embryos, believed that it arose from the neural crest, but the experiments of Campenhout (1935) and Yntema (1937) on amphibian embryos led them to the view that it was largely, if not wholly, of placodal origin. This view was supported by Halley (1955), who worked on the cat, and later by Batten (1958), who worked on the sheep. In fact Batten stated categorically that the otic placode was the sole source of the acoustic ganglion. It was thought that an entirely new approach to the problem, namely the use of mutant genes, might help to resolve the difference of opinion. The most suitable mutant for the present purpose seemed to be piebald-lethal (symbol s1; Lane, 1966).
Fgf and Hh signalling act on a symmetrical pre-pattern to specify anterior and posterior identity in the zebrafish otic placode and vesicle