Have you ever discovered that something you’ve believed your whole life is just plain wrong? Like, there is no such word as “drempt” or tool called a “sautering iron”?
What’s worse is when your long-held belief is not only wrong but incredibly foolish. Like that the yolk of the egg turns into the chicken.
I don’t know where this idea came from. Maybe it was my innocent grandmother, who once misunderstood my question of “Where does the sun go when it gets dark?” and explained about the sun going behind the earth, thus leading to my confusion as I tried to spot the sun zooming around to the backside of the earth continuously throughout the day–each time it went behind a cloud. Or maybe it was my not-so-innocent dad, who told me that the high-pitched sounds I heard when he fast-forwarded a cassette tape were tiny people who lived inside the stereo. Their voices were so high, he explained, because their vocal chords were so small.
Somewhere along the line, someone told me that the yolk of the egg solidifies into the chick. I never thought to reconsider.
At last I’ve been set straight. Last week I visited Scroggs Elementary School where one of the kindergarten classes received fertile eggs from Bracken Brae Farm. The class will keep the eggs in an incubator for three weeks until they hatch, then watch the chicks grow for nine days. The chicks will then return to the farm, where the hens will join the egg-laying flock. As I filmed the class, their teacher talked about the changes happening inside the egg. Here’s the real deal:
The hen produces the yolk, which gets fertilized (or not), encased in the egg white and shell, and laid. If the egg is fertilized, the chick embryo forms along with veins connecting it to the yolk, which nourishes it as it grows. There is a pocket of air at one end of the egg; on its last day inside, the chick pierces the air pocket and starts breathing with its own lungs. Then it pecks its way out. (Here’s a more detailed version with proper nomenclature. )
Here’s an animated version of this with some dreamy music.  It all makes sense until minute 1:58 when the newborn chick randomly turns into an upright fluffy yellow chick.
And here’s a photographic version with some old-timey orchestra music.  (Warning: lots of blood and veins! I only made it through the first half, actually. Then I skipped to the end to see if this newborn chick also morphs instantaneously into a fluffy chick, and it does! Not only that, the one chick then turns into FOUR fluffy chicks.)
So there you have it. Yolk ≠ Chick.
 This source and others say that at the end of the process, the yolk sac is drawn into the chick’s body. I can’t figure out how/why. “Stages in chick embryo development,” Mississippi State University. http://msucares.com/poultry/reproductions/poultry_chicks_embryo.html
 “Chicken Embryo Development,” Poultry CRC. http://youtu.be/PedajVADLGw
 “Development of a chicken embryo,” Vladimir Matveev. http://youtu.be/LKvez9duEHQ