Illustration showing the digestive and reproductive tracts of a female chicken. The oesophagus carries food from the hen's mouth to the crop (1st red pouch), where food can be stored for later digestion, or enter the proventriculus (2nd red pouch), or stomach, where acid and enzymes digest some of the food. Undigested matter moves to the gizzard (3rd red pouch), a muscular organ that grinds the food with stones to further digest it. The food moves to the small intestine (light orange), where further digestion and absorption of nutrients occurs. Undigested material is fermented in the ceca (brown), before entering the short large intestine (red, right) where water is absorbed, and being discharged from the cloaca. The hen's ovaries (green) release oocytes into the oviduct (pink) where layers of calcite are added to the egg until a shell is formed.