Day 14 and 15

On days 14 and 15 the chick's skull, beak, claws and scales on the legs all begin to become much firmer and the 'egg tooth', which will be used to break out of the shell, hardens. 

The air cell is growing to provide enough air to keep the chick alive, and the egg white is becoming smaller.  The embryo is now filling most of the egg cavity. If we tried candling the eggs now, eggs with chicks inside would simply appear dark, while eggs without chicks would have more light shining inside.