Squirrel teeth were decalcified in a modified formic acid-sodium citrate solution and sectioned longitudinally with a razor blade. The sections were stained with Harris' hematoxylin and eosin and viewed under a microscope using reflected light. Tooth development was used for separating spring and summer litters, while cementum annuli were used for placing the individuals into year classes. Magnifications of lOOX - 200X were best for aging by cementum annuli. It was found that spring and summer litters could be separated as accurately with tooth development and cementum annuli as with eye lens weights. Tooth sectioning had the added advantage of being able to separate the adults into year classes. Testing with formalin preserved known-age teeth showed that the razor section method is accurate for aging adult squirrels. Dry stored teeth are more difficult to age with accuracy, apparently due to the shrinkage of the cementum. / Master of Science