Cloaca and hardboiled eggs for a snack
Monday, October 1st, 2007The Missus was cracking a hardboiled egg for the kids. Spotz said he couldn’t believe that some dinosaurs ate other dinosaurs eggs. So I told him that weasles and snakes ate egg yolks, too. Then the Missus pointed out the obvious that we’re nest robbers, too. I said yeah these eggs would’ve become little chicks if we hadn’t grabbed them first.
The Missus then raised a very important question. Are those chicken eggs fertilized? I said yeah, sure. I mean how else would they get fertilized if they weren’t before they hit the nest?
Well as it turns out they just may not be. Check this page out for more info, but here’s the gist:
Birds, like mammals, use internal fertilization. Many species of birds lack a penis; instead, the male just has a genital opening (cloaca), which must be positioned against the female’s genital opening (also called a cloaca) for sperm transfer. Male chickens, however, do have a small penis to facilitate mating. In any case, after copulation, which only lasts a few seconds, the sperm quickly swim up the oviduct toward the ovary. The sperm can stay alive in the oviduct for several weeks, ready to fertilize the next egg cell (oocyte) that appears.
Oocytes are produced in the ovary, packaged with yolk within a thin protein membrane, and released one at a time into the funnel-like infundibulum of the oviduct. The oviduct is a tubular passageway leading from the ovary to the outside world. It is also an assembly line in which the various layers of the egg are constructed. After an oocyte-yolk package is released into the infundibulum, it lingers there for about 20 minutes. If sperm are present, then the oocyte is fertilized and becomes an embryo. But if no sperm are around (that is, if the hen has not mated), then the egg still proceeds down the assembly line of the oviduct. In this assembly line, albumen (egg white) is added around the yolk, shell membranes are added, and the shell itself is constructed. Finally, the complete egg is pushed through the vagina and out the cloaca.
If the egg has been fertilized, then the embryo inside has already divided several times but remains a group of unspecialized cells. When the egg is incubated at about 37 to 38 °C, the embryonic cells differentiate to form a chick, which will hatch after 21 days. If the egg has not been fertilized, then the oocyte within will never grow or divide, and the egg will never hatch. The eggs you buy at the supermarket are eggs that have never been fertilized.
Who knew?