Exactly. I didn't want to have to test them at all, but they were all late. I wish I knew what killed them, probably something environmental in this case because they appeared beautifully developed to about 18-19 days and my chickens have excellent feed. I tried to candle a few on about day 15 while the mama was off the nest and all the ones I checked had an air cell and the rest was full of chick. I'll have a better setup next time and hopefully have success. Thank you for the input!A very strong light is recommended but even then about all you will see is the aircell. If it has internally pipped, you will be able to see it and if you look at it long enough you will see it move but that's not a good thing to do, cause it may drop the internal temperature of the egg too much and would likely weaken or kill the chick.
In any given hatch, 1/3 of the embryos will (dis) early on, 1/3 will (dis) midway through incubation and 1/3 will (dis) late or just before pipping or soon after pipping. Various reasons for the deaths are numberous, some are nutritional, sequencing of RNA and DNA misdirected, genetical, or environmental.