Hello my friends

I have a problem in displaying the mesh grid in my plot3d graphs in maple 17. For instance, I when I type:

plot3d(x^2-y^2, x = -1 .. 1, y = -1 .. 1)

The graph has no mesh grid on it. I mean I am not seeing the black lines on the 3d surface. Can anyone help me to display the mesh grid please? Thanks.