You can take any of a variety of paths from the center to the edges ![alt text][1]. 

There are various ways to draw a a path from one vertex of a small square to the opposite one and get two symmetric pieces (although one can't just use horizontal and vertical segments). Then 4 of those little squares yield a dissection into 8 pieces.


  [1]: http://www.math.ucf.edu/~reid/Polyomino/Images/9omino36_6x6.gif