56 The shell of an egg is extremely strong, and a hatching bird spends hours or even days breaking this barrier to the outside world. Some nestlings are helpless and dependent on their parents for food. Others, such as the duckling shown here, are more developed and can fend for themselves within a few days of being born. Development of the embryo starts as soon as incubation begins. The shell and protective membranes protect the embryo. INSIDE THE EGG Albumen Yolk Embryo Air sac Sac for waste products Embryo Developing chick Shrinking yolk sac 1 Developing embryo The yolk and other nutritious fluids in the duck egg nourish the embryo. Within one week, the embryo grows and the different organs and tissues are formed. By the second week, the eyes of the embryo are visible. 2 Breaking the shell After 28 days, the duck chick, still enclosed in the shell, turns around to point its beak towards the egg’s blunt end. It breaks through the shell with the help of a special “egg tooth” – a sharp projection on its beak. 3 Cutting a circle The chick repeatedly pecks and turns inside the egg. It pushes with its feet to produce a crack that runs around the base of the egg’s blunt end. 12:10 Day 28 12:00 Day 28 Week 1 The egg shell has tiny holes that enable air to pass through it. Newborn duckling