Like everyone said it's the yolk being absorbed and that just means it wasn't absorbing the yolk as fast as it was developing or it said I want out before it bad absorbed the yolk. I had this happen before with both coturnix quail and bantam eggs I just leave them in the incubator or I put them somewhere nice like the brooder in a cup with paper towels in it and they usually survive okay, but there's always that one chick that doesn't make it. If you keep an eye on the chick and don't get it wet I think it will be fine.
