So you're thinking of hatching chicken eggs but you're not sure what to expect?
In this and the following pages we take you in detail through the different stages from day 1 to hatching at day 21 - slowly, carefully and with as much practical detail as you can take.
The candling pictures I use here and on the next pages are my own and follow one of my chicks right through from placing the egg in the incubator to hatching. This is what she looked like just a few hours after she'd hatched.
You can still see her 'egg tooth' - the little white tip on the end of the beak which chicks use to peck their way out of the egg.
A word of advice before we start ...
If this is your first time hatching chicken eggs and if - as I'm sure you do - you take it seriously, you can expect to feel two things : uncertain, and anxious. I certainly felt like that. It's only natural.
You've read all the books, you've seen all the questions on the forums. So much can go wrong at any stage ...
If you can, try to relax and enjoy the whole process. A mother hen goes through this without too much fuss - try to take a leaf out of her book. Yes, things can go wrong - but if you've chosen eggs wisely, if you're careful and you don't panic, all will be well. I promise!
The answer is - quite a lot. It may not seem like it, and you won't be able to see much of it at least initially, but ever since the egg was laid it has been developing. It will have stalled once the hen was no longer warming it, but make no mistake - if you have a fertile egg, development has already started before the egg goes into the incubator. Incubation kick-starts the process again.
Days 1 and 2 of incubation see the start of growth for everything of huge importance to the embryo : the head, ears, eyes, spinal column, nervous system (including the brain) and heart. As early as 72 hours after the start of the process, tail, wing and leg buds appear and the heart begins to beat.
By day 4 the toes and tongue have begun to form (yes, chickens may not have teeth but they do have a tongue!) and on days 5 and 6 the crop, reproductive organs and beak start forming and the wing can now bend.
Here's a diagram of the egg at day 5. The allantois is part of what in a human embryo we would call the umbilical cord and is responsible for getting rid of waste. You'll quite often see be able to see it left behind in an the shell after the chick has hatched. The amnion or amniotic sac is a membrane which surrounds and protects the embryo during its development.
On day 7, the leg is able to bend and a ridge of 'papilla' or glands form where the the feathers will appear on the tail and thigh.
By the end of this first week, your chick is one third of the way to full development.
The shell of the egg doesn't change at all on the outside until the chick is ready to hatch much later in the process, when she will start to peck through or "pip". Until then, if you want to see anything you'll need to invest in a candler - either home made or shop bought. Both are good.
There's really not much to see at this point. Initially the egg will look clear apart from the air cell which you'll see at the 'fat' end of the egg. As time goes by you'll notice this air sack become larger and it's here the chick will eventually hatch.
From day 2 to 3 you'll be able to see the yolk of the egg. When I first saw this, I was hugely excited - I thought it was the embryo. That's how much I knew.
But wait! - What's this?
From about day 4 or 5 in a properly developing egg you'll start to see tiny spider like markings appearing in the yolk area when you candle your eggs. These are easiest to see in white or light-coloured eggs - in a dark-coloured egg like a Marans they're much more difficult to spot.
This is the start of the embryo's visible development. The 'spider legs' you can see are the embryo's blood vessels, which will become much more well-defined over the next several days.
The next few days see the development of the blood supply to the developing embryo, and the eye becomes far more prominent too.
If you look closely, you can see the outline of the embryo developing. It looks like a darkish ring around the eye. You can also see at the bottom of this picture that the air cell has started to get a little larger. This too will become more obvious with time.
In a lot of ways, the first week is the worst. Once it's over you can see your chick developing and you'll also be able to tell whether you have eggs which are infertile and not going to develop.
Now all we have to do is get through the next two weeks and I'm telling you - they will fly by!
If you want to go through the first week of this process again you can return to the top of this page by clicking here, or you can move on to an overview of the next stage of incubating and hatching your chicken eggs by clicking on the picture below.