Abstract 1. 1. During hibernation the epithelial cells of the stomach in ground squirrels divide upon spontaneous emergence from hibernation. In torpor periods, mitoses are blocked up. 2. 2. In animals which have come out of hibernation in spring, one peak of mitosis has been recorded in the first few hours after emergence, and another 3 or 4 days later. 3. 3. In summer the mitotic index is low.