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The histological structure and morphometric and some histochemical indices of thyroid gland of maral as a subspecies of red deer at the postnatal stage of ontogenesis were studied. It was established that the gland was structurally formed by the time of the birth. C-cells are detected at 6 months of age. With age, the ratio of follicles of different sizes changed: smaller forms predominate in newborns and those 6 months old, medium and large predominate in adults and in old deer. Histological, morphometric, and histochemical data indicate to activation of the thyroid gland in the period of intensive growth for up to 6 months and a gradual decrease in activity over the next years of life. During aging, along with an increase in stromal elements, large follicles with colloid are stretched and resorption processes in the follicles are reduced.

Histological structures and morphometric and some histochemical indicators of elk's adrenal gland development as subspecies of red deer in prenatal and postnatal ontogenies stages was studied. It was found that the growth of the fetus adrenal glands weight and the thickness of the structures adrenal glands fragments continue throughout the prenatal period of ontogeny. The cells of androgenic zone with single wandering sympathogoniae are differentiated in the adrenal glands in the second month of development. The androgenic and definite zone and the adrenal medulla are differentiated by the third month of development. At the 4 months, adrenal gland cortex zona glomerulosa and zona fasciculate-reticularis are differentiated; zona reticularis is differentiated only by the seventh month. By the eighth month, the structure of adrenal glands corresponds to the adrenal glands of a newborn. Full structural formation of the adrenal glands takes place in young animals by age 1.5. Obvious structural changes were not found late in the postnatal stages of development.