Maya Help Please!!

I'm trying to make, in Maya, a nucleus divide into two separate nuclei. Alan showed us how to do this by merging two spheres somehow, so that as they got further apart from each other, the middle seemed to stretch them both. This method didn't involve actually messing with the vertices or anything on the spheres themselves, but it actually added another piece of geometry in the middle of them.

Do any of the pros out there know what the tool or option is called to make this? Image related; it's the splitting of nuclei that I'm trying to make. You can see where the middle of the two blobs stretches until it breaks.

Thanks! ! ! ! ^.^