[Morphological characteristics of the cardiac myocytes of the frog (Rana ridibunda) in the cardiogenesis process].

An investigation has been performed on formation of the cardiac muscle tissue and ultrastructuraluralural organization of the cardiac myocytes in the frog (Rana ridibunda) at the age of an embryo and larva, as well as in young and mature species. A principle similarity in processes of ultrastruct differentiation of the cardiac myocytes has been revealed in lower and higher Vertebrata. Observations on dynamics of the proliferative activity in poorly differentiated cardiomyocytes demonstrate that certain asynchronity in the development of various parts of the frog heart appears rather early. Owing to the quantitative ultrastructural analysis performed, it is possible to conclude that the material of yolk plates is used for organelle synthesis that ensures the specialized function of the developing cardiac myocytes.