The last but one stage of incubation is a time of massive change as our chick prepares to breathe for itself. It's an exciting - and worrying - time!
The chick is getting ready to hatch.
If we opened the egg today we'd see that the chick is getting larger and the yolk sac is getting smaller. That's because the yolk is now about halfway inside the chick's body. It needs to be completely enclosed before the chick can safely hatch.
As the yolk decreases during today the chick fills the shell completely, apart from the large air cell.
There's a lot going on during today as we get very close to hatching.
The incubated egg at day 20.
The chorioallantoic membrane, which the chick has been using to breathe in oxygen and breathe out carbon dioxide, is now starting to lose importance as the chick will soon start using its lungs to breathe for the first time. The membrane's blood vessels decrease and the membrane itself becomes quite sticky.
It's this membrane the raised incubator humidity is keeping moist during the last stage of incubation and throughout hatching. If it dries out, it will harden and the chick won't be able to 'pip' its way through.
It's important that the egg is not candled today as we're very close to hatch and the incubator lid should remain closed to preserve the humidity the membrane needs to keep moist.
As the moisture levels begin to build for hatch, you'll probably start to see some water droplets on the inside of the incubator.
Leave the eggs alone! They know what they're doing!
We should be preparing for brooding today. Our chicks will need a home to go to once they've hatched and dried off.
So stop watching those eggs obsessively (I know you are, I've been there!) and start planning ahead.
The main thing that goes wrong today and tomorrow is that we become too anxious about what's going on - or not going on - and try to "help". Many full-term chicks have been killed by well-meaning owners trying to assist them out of the egg too early.
Although chicken embryos go through definite stages of development, the speed with which they go through incubation varies.
So although on average hatch day will be 21 days after setting the eggs, it's not unusual for it to take longer. I've had perfectly healthy chicks hatch at Day 24.
I know it's an anxious time but honestly - everything will be fine. Relax.
I'm not seeing any signs of 'pipping'. Should I make a hole for the chick to breathe?
Absolutely, definitely, categorically - NO!
Chicks develop at different rates. Although the stages I've described in this series are followed in sequence, some embryos will follow them more quickly than others.
There's all kinds of reasons for this. The egg might have been incubated for a while by a broody hen before it's collected for mechanical incubation, so might be a few hours ahead of others.
This little chick hatched in my Brinsea Octagon 20 incubator about 12 hours before the others.
Or the temperature in the incubator might have fluctuated slightly and been a little cooler at some periods, making development slow down so that pipping and hatch is a little behind.
The really, really important thing for today and tomorrow - and days after that if necessary - is - don't panic!
Leave your chicks to their own devices. They know what they're doing. Nature is a wonderful thing!
On each day of this incubating series I've been featuring a photo of one of my own chicks.
It helps us keep our minds focused on what we're working towards - a healthy, happy chicken.
This is one of my Black Copper Marans babies at 12 days old. Notice the beginnings of feathering on the legs - one of the characteristics of this chicken breed.
Is there a question you'd like to ask? Or perhaps your chicks have already hatched?
Please feel free to leave a comment below. I'd love to hear how it's going!
The first link is to an overview of days 20 and 21 of incubation. It's nothing like as detailed as this series, but useful if you want a quick read of what's ahead tomorrow.
Click on any of the images to go to the pages.
Have you joined my incubating and hatching group yet?
If you're having a go at hatching your own eggs and it's new to you, you might want to consider joining my free 28-day series called "Hatching Happy Chickens".
You'll have e-mails personally delivered every day describing that day's developments in the incubation process, and pointing out as this page does exactly what you need to be doing.
It's free, and it's fun! Don't miss out - click on the pic to have a look at more information about exactly what you'll get.
The easiest way to follow my hatching series is to sign up for the e-mails. However, if you'd rather not do that, these are links you need to work logically through the series.
'The Incubated Egg' image is a commissioned artist's impression and, like all images on this site, is subject to copyright under the Copyright Law of the United States of America 1976. Under no circumstances is permission granted to copy or otherwise use this image.
All other images of candling on this and other pages are my own and are not to be used without permission.
If you wish to use these or any other images on this site for educational purposes you are required to contact me by using the form to be found on this page. For my full copyright policy see this page.