I had 8 eggs in the incubator and 5 under a broody I candled the incubated 1's at day 7 and 7 of them were like a black smudgy spot and in 1 I could see the veins I cracked 1 of the 7 open and there was no development I cracked open the other 6 and none were fertile so if u can't see the veins they are probably not fertile