Chicken Development Glossary

Cross Section of a Newly Laid Egg

chalaza - a spiral, rope-like strand that anchors the yolk in the thick egg white. There are two chalazae anchoring each yolk, one on the top and one on the bottom. (The plural of chalaza is chalazae.)

germinal disc or blastodisc - a small, circular, white spot (2-3 mm across) on the surface of the yolk; it is where the sperm enters the egg. The nucleus of the egg is in the blastodisc.

inner shell membrane - the thin membrane located between the outer shell membrane and the albumin.

outer shell membrane - the thin membrane located just inside the shell.

shell - the hard, protective coating of the egg. It is semi-permeable; it lets gas exchange occur, but keeps other substances from entering the egg. The shell is made of calcium carbonate.

thick albumin - the stringy part of the egg white (albumin) located nearest the yolk.

thin albumin - the watery part of the egg white (albumin) located farthest from the yolk.

vitelline (yolk) membrane - the membrane that surrounds the yolk.

yolk - the yellow, inner part of the egg where the embryo will form. The yolk contains the food that will nourish the embryo as it grows.