this is my very first experience hatching eggs..i made my own bator and am havin a bit of trouble holding the temp at the EXACT spot but today is day #4 and me and my kids candled and THIS MOM WAS THRILLED to see a mass with veins in 3 out of 4 eggs!!!!! the eggs came from our own coop (2 roosters and 4 hens-austrolorps) SOOO the 4th egg had a bubble at the top and a bubble at the bottom but a gray/black mass in the middle...what does this mean???? do not plan to candle for another couple of days..probably day 8-10...let me know what advice and what you think!!