What do they generally look like at around 16-17 days? I see a definite air space that looks the right size according to the air sac diagram. But I'm not sure it's a 'bubble.' Is it supposed to be an intact bubble, and if so, what happens if it's not? Can a chick still hatch if there's air in the egg but it's not an intact bubble? Or am I seeing the right thing but interpreting it wrong? Help, I'm really worried.