Analised dynamics of morphophysiological indications during the life cycle of the bank vole Myodes (Clethrionomys) glareolusSchr. in the conditions of the northern periphery of the range. According to the results obtained, the individuals spring and summer generations are characterized by an exceptionally high rate of development and growth, and a corresponding increase in the main internal features. Individuals of the later born generations are characterized by a slower increase in weight of internal organs by autumn, and a slight decrease during winter time. However, late born individuals experience during spring, a rapid maturation and growth, accompanied with a sharp increase in morphophysiological indexes. The level of the variability of the internal features is very high, with spleen size having largest variation, followed in descending order by the size of thymus, adrenal glands, liver, heart, kidneys, and length of intestine. Because of the small size of the body and the large relative size of the heat transfer surface, the animals of the studied species have efficient level of metabolism rate and cardiac activity. Small mammals compensate the large energy requirements and the constant thermal deficit associated with them by exceptional lability of adaptive reactions. This manifests itself in the regular seasonal and age dynamics of the main morphophysiological (interior) indicators. It has been established that the basis of adaptive reactions aimed at successful overwintering is the minimization of metabolic processes, the adaptation of use of smaller amounts of energy and the general inhibition of vital processes.