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a solid formation on the surface of the mechanoreceptor cells in the organs of equilibrium of some invertebrates and all vertebrates. Otoliths of different animals vary in origin, size, and structure: they can be secreted by cells or introduced from outside, for example, grains of sand serve as otoliths in crayfish. Mammalian otoliths are usually crystals of calcite (CaCO3) up to 10 microns (μ.) long and 1–3 μ wide.
As otoliths shift in response to acceleration and changes in body position, they mechanically irritate the underlying ciliated receptor cells, which then send appropriate signals to the brain.
The action of otoliths has been demonstrated in experiments with crayfish. The grains of sand that serve as the crayfish’s otoliths were replaced during molting by iron filings, and a magnet was placed above the animal to attract the filings. The crayfish reversed its sense of orientation, turned over, and swam with its abdomen up.
O. B. IL’INSKII