[Paraview] Clip polygonal data?

[Ken Olum]

I'm trying to visualize some strings.  I have them as a polygonal mesh
containing my set of points and each string represented as a polyline
going through all its points.  Then I visualize the strings with the
Tube filter, which works great and looks beautiful.

But now I'm trying to extract only part of my volume.  It looks like
Clip is the filter for this, but Clip returns unstructured grid data,
on which Tube does not operate.  Also Clip disconnects my strings
into individual lines connecting the points in pairs.  

Is there a solution?  I'm not picky about what happens at the edge of
my volume.  For example I'd be happy for it to keep only the parts of
the polylines that connect points inside the volume.

Thanks.

                                        Ken