The histological changes with the progress of age in the pineal gland of dogs were studied. Twenty dogs of both sexes clinically healthy were used. Two dogs from different ages were chosen from 2 days of age up to 4 years of age.
The size and shape of the pineal gland showed no or little change with the progress of age. The pineal recess of the newly born dogs consisted of arrow cleft remained unchanged up to maturity. The changes were classifiedinto3stages. The first one, the parenchyma was highly cellular with either randomly distributed cells or cords-like structure. The main cellular elements were the pinealocytes and few glial cells. The mitotic figure was predominant. From the second stage onward, the number of pinealocytes decreased and the number of both glial and pyknotic cells increased. The glial filaments appeared long and branched at 4 months old dogs. The pigmented cells appeared at 2 days old dogs and became more with the advances of age.    
In conclusion, the decrease in the number of pinealocytes in our results could be attributed to either the pinealocytes undergoes differentiation to other cells similar to glial cells, due to change in nuclear morphology and the presence of large numbers of glial filaments, or by pyknosis in which the pinealocytes degenerated. The last suggestion augmented by wide separation of the cells from2years old dog onward.