Wow - we're hatching chicks in an incubator for the first time. The chicks actually have umbilical cords which attach to yolk sacs, which attach to membranes attached to the shells . . . . . very much like a human placenta but instead of lining a uterus it lines a shell. Umbilical cords attach to belly buttons - so therefore chickens must have belly buttons!
Never know what you're going to read on a cycling forum, eh?

