ABSTRACT
The layers in recording structures appear because parts that form with a certain periodicity differ in morphology, optical density, and their propensity to be stained with histological dyes. Such parts of a recording structure can be called its elements. In growth layers, either only two elements which differ in optical density and stainability can be found, or the pattern can be more complex, because there can be several additional elements inside a layer. Estimation of the content of mineral substance in adjacent transparent and opaque bands was carried out by several authors, and the results were contradictory. By impregnating ground sections of the teeth of marine mammals with AgNO3, it was shown that the transparent band is hypercalcified relative to the opaque one. The double elements in growth layers of recording structures are formed because in a given individual, owing to its genetics, there are not two phases, but a more complicated rhythm of seasonal growth.
