That's a good idea, Tom. He had one, actually, but I could still see through the side that he'd come out, and then that he'd stayed there for a long time, so I took it off for the picture.
He was out this morning, and it's the tiniest thing I've ever seen--2g! No one else has slit the egg, so I guess this one is early. It has a little hanging umbilicus, so it's in a deli cup with a little water, which worked for me last year. The umbilicus is pretty dry, though, so I don't expect it to be a problem. It looks like it has a slightly concave area on the ventral side (in the white area near the neck). Maybe this guy isn't hypo, but preemie? Dunno. I know others have had 2 g hatchlings that have lived, so I'll give it a chance, but I'm not going to hold my breath.