How to create a 3D mesh for a sphere not just a surface mesh

I created two spheres
with the Sphere class in fenics 2.2
"subtracted" them to obtain an object with an inner and outer boundary at radii 10 and 2 units.
This yields however only triangulations for the surfaces, but not for the sphere!

asked Jun 28, 2013 by moritzbraun FEniCS User (1,390 points)

I did find the answer by googling
namely you need to
say
Mesh=Mesh(Sphere,integer)

commented Jun 28, 2013 by moritzbraun FEniCS User (1,390 points)

...