Hi, I am new to "home grown" chickens. My flock has come from other peoples leftovers and some poultry swaps here and there. I have never candled before today and can't seem to find the answer to what I am looking for. I have a Silkie X sitting on 6 eggs....I decided to let nature do it this time around. She started with 3 eggs and about a week later 3 more have shown up. All are fertile with the youngest looking to be about 8 days old. However, 3 of the 6 eggs are SO dark inside that all I can see is the air sack. What does this mean??? They feel "lighter" than the others. Thanks!