White Sack in Egg?

[OreoPlymothRock]

Hello, I was baking and when I cracked an egg open this thing fell

out! There was a yolk in the egg, whites in the egg, and this! Does anyone know what this is? It is somewhat hard, but squishy and you can definitely tell there is some fluid inside. It happened before with another chicken. Any help is greatly appreciated, thanks! Here is a pic:

 

[Granny Hatchet]

I THINK they are called meat eggs. I dont know too much about them but that may give you a starting point.

 

[lazy gardener]

I believe it's a LASH egg within a regular egg. FMI, do a google search.

 

[DRGLENNON]

It kinda looks like a soft shell egg was inside another egg. Hopefully just a temporary hiccup in laying process. Good luck!