THE EGG Fresh eggs are one of the main reasons that people keep chickens, so it can be useful to understand what they’re made of, how they form in the chicken and exactly what makes a good egg. In the chicken’s natural life cycle, the egg is an incubation chamber for a developing chick. The egg contains everything the new chick needs during the three- week incubation period and the first couple of days after it has hatched – which is why eggs are so packed full of nutrients. The egg is made up of 5 main sections Air cell Yolk Cuticula Eggshell Chalaza Germinal disc Vitelline membrane 3 5 4 1 1 2 2 The eggshell, which consists mainly of calcium carbonate, is quite porous, containing nearly 8,000 minute holes through which gases and water vapour can pass. The shell membrane (cuticula), which acts as a barrier against bacteria. The layered albumen (egg white) including the chalaza, which hold the yolk in the centre of the egg. The yolk. The germinal disc, which can be seen as a very small spot on the centre of the yolk’s surface, is where the chick develops in a fertilised egg. 5 4 Thick albumen Thin albumen 3 3 3 THE CHOOK BOOK | 9