Coloured scanning electron micrograph (SEM) Emu eggshell surface with tiny pores (Dromaius novaehollandiae). Calcium carbonate crystals make up the Emu eggshell. Bird eggshells are semipermeable membranes composed of mineralized calcium carbonate and filled with thousands of pores. The eggshell protects the embryo inside and controls the passage of air in and out of the egg interior through tiny pores. Lying under the eggshell is an anti-bacterial membrane (not shown). This membrane allows the exchange of carbon dioxide and oxygen between the developing embryo and the external environment. Dromaius is a genus of the 'ratite' bird group present in Australia. A ratite is a diverse group of large, flightless birds of Gondwanan origin, most of them now extinct. Magnification: x10, 665 when shortest axis printed at 25 millimetres.