Emperor Penguin: Inside the Breathing Egg
Kicking back before getting down to the hard work of hatching--a several-day process--a late-stage emperor penguin embryo (shown in a digital illustration) breathes easy inside its egg, which is resting on the father penguin's feet while Mom is on a months-long fishing trip.
Unlike developing humans, a baby penguin can't tap into the oxygen in its mother's bloodstream. Instead, its umbilical cord is linked to blood vessels in a membrane attached to the egg's inner wall. Oxygen enters the embryo's blood via microscopic holes in the shell--turning the egg into a kind of surrogate lung.
After 64 days of development, the baby penguin will slowly smash its way out, and its mother, with any luck, will be waiting with fish. Related Video: Penguin in the Egg
ON TV In the Womb: Extreme Animals airs Saturday, May 16, 2009, at 9 p.m. ET/PT on the National Geographic Channel. Details >>
Illustration by David Barlow Photography