I am 7 days into an incubation. Of Leghorn. Eggs. Most have veins, but I only see embroys in some. Of them.are the ones with just veins not fertilized or just not developing as. Fast?
If you see veins they are probably developing. Check them again in a a few days and see if they are any further along. Some may develop faster than others. Also the incubator my have cool spots and warmer spots. The eggs in the warmer areas may develop a little quicker depending on how close they are to the heating element.