The age of the embryo when the egg is laid varies. Peregrines tend to lay eggs during the night or early morning or in teh evening.; if the egg is not complete until later in the day, it will probably not be laid until the next day. The rate of development of the embryo once the egg is laid also varies. If the eggs are cooled after laying, development of the embryo ceases until the temperature rises again. Development can resume even after the eggs have been cooled for several days. The temperature of eggs incubated by their mother is 106 degrees Fahrenheit The temperature of course will vary when the peregrine leaves the eggs to eat, etc. All of this affects the rate at which the embryo develops and, therefore, how long it takes for the chick to hatch.
The beginning
First Day: The Journey Begins
Before the Egg is Laid:
* The egg is fertilized.
* The zygote divides and begins to grow.
* The cells segregate into groups of specialized function.
* The embryo nearly stops growing between laying and incubation.
During Incubation:
* The area pellucida and area opaca of the blastoderm develop.
MAJOR EVENTS
Second day:
Embryo in the 4th day*27 hours: The alimentary tract appears.
*28 hours: The brain crease begins to form.
*29 hours: Somites appear.
*31 hours: The brain and nervous system begin to form.
*32 hours: The head fold begins to form.
*34 hours: Blood islands appear.
*35 hours: The eyes begin to form.
*37 hours: The heart begins to form.
Third day
*52 hours: The ears begin to form.
*58 hours: The heart starts to beat
Fourth Day
Yolk in the 4th day*76 hours: head turns to the left
*78 hours: Amnion has enclosed the embryo
*80 hours: Allatois begins to form
*88 hours: The beak begins to form.
*92 hours: The leg begins to form.
*94 hours: The wings begin to form
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