I tried to take some pictures of the incubating eggs while they were being "candled", which involves holding a flashlight up to the egg in the dark, illuminating the inside. As a chick begins to develop, the egg is filled by black. You can also see the "air sac", which either expands or contracts depending on the humidity in the incubator. Keeping an eye on this helps you track the moisture in the bator, and thus helps prevent hatching issues.
The pictures didn't turn out so well; for some reason I couldn't find a good setting to take pictures on. But I did get too pictures, one of the air sac and one of the chick---which appears to be a lump.
These pictures are of one of the game-mutt eggs ( it has a very light-colored shell, which makes candling easier), and is a week into incubation. Two more weeks to go.
When the chick gets larger, and closer to hatching, you can actually see it moving around inside the egg!
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