Egg containers are a common way to store and transport eggs. Uteri, nests, HENS, ovisacs, SACS, and CARTONS are all types of egg containers. Uteri are the membranous SACS in which eggs are formed and stored in the female reproductive system. Nests are structures made by birds to hold their eggs. HENS are female birds that lay eggs. Ovisacs are protective membranes that surround the eggs of certain animals. SACS are small bags or pouches used to store items. CARTONS are boxes or containers used to store and transport items.