Agassiz research scientist Fred Silversides has an answer to a mysterious egg we featured in a recent edition of The Observer.
Mortier George was blowing out an egg from his own chicken coop, in order to create a "fake egg" to encourage production, when he discovered another egg inside it. He brought it to the newspaper in hopes of finding out what would cause that, and how common it is.
Silversides explained it by saying the egg starts out with the yolk, which is ovulated from the ovary. It's then picked up by the oviduct and passes through the duct. In the process, the yolk gains the shell membrane and eventually the shell.
But things don't always go as planned.
"There are things going in both directions," Silversides explains. "If for some reason the egg gets pushed backward, the hen will see it as a yolk and it gets another shell."
It sometimes happens with tissue
In fact, he points that in the past, some people would have a bit of fun with that fact, through surgically inserting a piece of paper with a message on it.
"This was before my time but you can send a message through an egg," he said. "She'll produce an egg out of anything that goes in that oviduct."
The double shelled egg could also be a sign that the hen is getting beyond her best reproductive years, he added.