Voronoi 3d help

I think this is a simple question but i've just discovered voronoi's today which kind of do what i want them to do.

My problem is, when you create a voronoi in grasshopper, it creates this box.  My question is how can i remove that box so i'm left with just the skeleton? 

The image describes the box i mean and the second image is just one i took off google but it's the skeleton i'm talking about.