Acetylcholinesterase activity in the embryonic chick's inner ear.

Putative cholinergic efferent endings, as demonstrated by the presence of a localized acetylcholinesterase reaction product and visualized by phase-contrast microscopy, appeared in the lagenar macula and cristae ampullares on the 11th embryonic day (ED) and in the basilar papilla by the 13th ED. During the course of development, the reaction product became denser and more sharply defined, reflecting the maturation of efferent endings.