What should you expect to see during this second week?
Apart from the first sight of those "spider veins" at around day 5, the second week is the most exciting phase of hatching chickens.
We'll see the embryo go from a tiny cluster of cells to a moving chick.
If we had an egg heart rate monitor, we'd see the heart beating strongly.
In this article, we look at written and photographic detail of what to look for in a properly developing egg.
The candling pictures I use here and on my other incubating and hatching series are my own. They follow one of my eggs right through from the start of the process to hatch.
This is what the egg that you'll see today looked like five days after she'd hatched into a lovely Light Sussex hen.
See how she's already getting nicely coloured feathers on her wings?
This part of hatching chickens is the most interesting (apart from the hatch itself, obviously!) because there's such a lot going on, and so quickly.
It's possible to see your chick growing quite fast until, by the end of this stage, she's filling the bulk of the egg. Here's what the embryo would look like if we could break open the egg each day (which, obviously, we can't...).
Below is a detailed diagram of the egg at day 10.
By the end of this period, your chick is two thirds of the way to full development.
The candling process during these stage is fascinating. Although it's not wise to candle every egg every day, I admit I find it hard to resist when there's so much going on.
By the start of this week the embryo will be clearly visible when you candle the egg. The eye will become more prominent with time but even at this stage it can be clearly seen. Look for a large black dot.
It looks completely out of proportion to the rest of the embryo but don't worry - you're not about to produce a monster chick!
See how by this point the air cell at the bottom of the egg is growing? When you candle, you should be able to see its growth very clearly.
It's a critical part of the 'pipping' process because it's here the hatching chickens will initially break through and take their first breath.
The eyes are now also clearly visible as dark blotches. Sometimes you can only see one, sometimes two - it depends which way the chick is lying.
When I first saw this, I thought my egg was having twins!
Now you can really see how quickly this chick is growing.
The vascular system - the blood vessels keeping it alive - are becoming very well developed. If you compare this to the diagram here you can see that the 'allantois' is also growing.
This is an important part of the embryo's growth. It gets rid of waste products in much the same way as the umbilical cord in a human embryo. Without it, the egg would die.
The chick is doing more of the same. You may be able to see it moving about inside the egg although, as it grows, it has less room to wiggle around.
You can see I'm having more trouble candling now because the embryo is starting to fill the space. If you have the same experience, try holding your hand behind the egg to try to get a better view.
I've turned the egg around today so that there's something at least to show you! The other side of the egg is now full of chick so just looks dark.
The veins are developing nicely. This is a strong, healthy chick!
From now on, though, it will become increasingly more difficult to see the embryo's development.
Your chicks only have a short time to go before we need to stop candling them and wait for hatching to start!
I hope you're able to enjoy this second phase of the hatching chickens process as much as I do. The anxiety of the first few days is over, you know your eggs are fertile, you've taken away any that aren't, and you can settle back and relax.
Just one more week to go. Are you ready to meet your chicks?