So this is my forth round of hatching duck eggs (Cayuga and Indian Runners). I have this one Runner egg that appears to have no Air sac at all, but veins definitely are growing. Today would mark day seven of incubation. When I candled this egg I couldn't find a visible air sac at the bigger end of the egg, so I thought that maybe it was one of those ones that had the air sac at the wrong end. When I checked though, I didn't see an air sac there either. It's a little lighter in color at the narrower side of the egg but I'm not seeing a defined air sac. The veins looks like they're going towards the thicker end of the egg. Has anyone seen or heard of this before? What should I do?