We’re halfway there! Chick development is really starting to speed up. The legs are developing scales, the toes are growing and curling, and the tiny comb grows a serrated edge. The main blood vessel – the aorta – can be now be seen along the neck. The chick’s intestine begins to push its way into the yolk sac. This happens so that the chick can fully absorb the yolk before it hatches and “take its lunch with it” when out of the shell.
The eyelids begin to enlarge and the nose opening is growing and narrowing and the beak continues to harden. The comb is still forming and the toes, which are now separate, begin to grow claws at the end.
The chick is moving around a lot now, the embryo is swishing all around in the amniotic fluid. The egg tooth is growing bigger and the beak is more pronounced. That chick is really starting to grow!
The third eyelid, a transparent membrane which keeps the eye moist and free from grit is developing today. It’s clear so that the chicken can keep an eye open – literally – for predators even as it blinks.
The pterylae or feather tracts – the part of the chicken’s body from which the feathers sprout – are developing today and the down the chick will be born with, known as natal down, is growing.
On day seven, digits begin to appear on the feet that will grow into toes. Also, very early forms of feathers begin on the tail and thighs. We can finally see the eyes and a tiny comb appears on the head. Today is when the egg tooth begins to grow as well.
The beak begins to grow and the wings begin to bend at the elbow, sometimes you can see movement when candling at this stage. The gizzard begins to form and the intestines begin to loop.
On the fifth day, the bones are now beginning to form. The legs and the beak are growing and both legs and wings will be able to bend within the next twenty-four hours. Today is the big day when we find out if the chicken is a girl or boy!
At the end of the third day of incubation, the beak begins developing and limb buds for the wings and legs are seen.
The embryo’s blood vessels are now forming and the heart begins to beat! The chick’s ear is beginning to form as are two separate circulatory systems, one to provide the embryo with nutrition and the other to take away waste.