A brief lesson in Oology
The Study of Birds eggs is called Oology. The yolk of a bird’s egg cradles the germinal disk (blastodisk) from which the embryo chick develops, and it provides the embryo with food. Outside the yolk are the albumen, or egg white, and finally the shell. Each part is built in a series of concentric layers, and each is enclosed in protective sheaths. The chalazas are twisted strands of fiber that help to hold the yolk in the center of the egg. They are attached to the albumen at one end and to the yolk at the other.). The shell stops the egg from drying out but is porous enough to allow oxygen to filter in to the developing chick. It also protects the egg from most bacteria. A crack in the eggshell a few days after laying is usually fatal, as it allows bacteria to penetrate. A crack will also cause excessive moisture loss. With the embryo closed off from the outside world by the shell there is the problem of how to dispose of excreted wastes. Here is where the allantois is so crucial, as it serves as the embryo’s garbage bag. (when the chick hatches, the accumulated wastes can be found sticking to the inside of the abandoned shell.) In most birds while these membranes are forming the embryo itself continues to develop differentiating the various organ systems. 2-6 days after the egg is laid, the heart & large blood vessels are visible within the egg. 8-10 days the eyes are prominent, 10-14 days the brain becomes visible through the transparent skull, with limbs becoming apparent. Finally just before hatching the “egg tooth” (the knob on the end of the beak which the chick uses to break out of the shell) is visible. The duckbill platypus and the spiny anteater are the only mammals that lay shelled eggs. All other mammals develop from shell-less eggs and remain inside their mothers' bodies until they are born. All birds lay their eggs before the eggs are ready to hatch. The egg is normally laid blunt end first. Double & triple yolks result when 2-3 ova are released from the ovary at the same time, most times only one of the yolks are actually fertile. Due to the lack of growth space within the egg shell, the double/triple fertilized eggs are unlikely to produce live chicks. The largest know egg was from a dinosaur, recovered in China which 18 inches long. The largest birds egg is from the extinct giant elephant bird (Aepyornis Maximus) of Madagascar which was 15.4 inches long with a volume of 2.26 gallons. Today the largest bird egg is from our Ostrich with is 8 inches long. The age old question of which came first the chicken or the egg? It’s now been settled. The Chicken came first. Go to www.howstuffworks.com/question85.html for the scientific answers you seek.
Illustration by Compton’s 1995 New Media Encyclopedia
Order a Polo or T Shirt | Become a Member Today
Upcoming Events | Main Page | About Us | Forms
Birdie Education | Our Mission | Our Supporting Sponsors
Bird of the Month | Non-Profit Bird Clubs by Location
Non-Profit Bird Clubs by Bird Species
Bird Food, Supplies, Cages, Toys, Accessories & Services
If you have found a bird click here!
updated on 5/28/05
