Fig. (15) Histogram showing the number of mitochondria per each adrenal medullary cell, either adrenalin cell or noradrenalin cell of respective animals in 10 groups during the development and aging from fetal day 19 to postnatal month 24. The number of mitochondria per cell increased from perinatal stage to postnatal day 14 and to postnatal month 2, then did not change to month 24.