It's pretty cool, actually. Four eggs had live chicks in them as of last night: (Should I warn anyone who may be sqeamish that these photos are realistic? Nah!!)
Eggs should look like this on Day 10 (photo credit, Backyard Chickens Forum)
The little dark area is the embryo, which curves around like a 'C' - sometimes you see both ends and not the middle, as in the first photo. What really tips you off is that they move!!!! They still have plenty of room to swim around inside the shell, so you can see the little head bob and move from side to side, and what looks like they could be wings.
These are all white eggs, so they can be seen very clearly. Even though all mine are pale beige, not even brown, they are much harder to see. I could no longer see veins on mine. They looked more like the last photo above.
This is Day 11
A couple of my eggs looked like this, like they are more advanced. ?????
And even like this, and this photo is of a Day 12 embryo!
But............ a couple of them looked like this. :( A shadow where the yolk is, but definitely nothing going on inside.
photo credit - Ohio State University
One of the eggs (I think a Cochin egg) looked 'clear' from the beginning. I had several marked with question marks, but one I thought was alive now looks like this. Apparently eggs beginning to form, then dying before they fully form and hatch, are common. So, I finally gave up on the 'clear' ones and only put four back under Abigail - a Cochin (Mille Fleur, I think) and three Buff Orpingtons. (there had been a Black Orp egg, but it was one that didn't make it) So sad, and very hard to give up on, but it was obvious, even to me.
Now I just hope all make it to hatch, and that they're all girls!!!!
Waiting and hoping at Wren Cottage........