I had 42 chicks hatch yesturday

. I had 3 that didnt hatch so I left them in and when i got up they had hatched. 2 are in good shape but 1 has a 1/2 inch round sack hanging off his butt

. It looks like its got poop in the sack. Has anyone had this happen? Do I leave it alone? Do I cut it off or open

? please help. I hate to see it like this.