Development of a Chicken Embryo Day by Day

By Pyxis · Jan 31, 2017 · Updated Apr 24, 2017 · ·
  1. Pyxis
    This is an explanation of what is happening each day as a chicken embryo develops, complete with candling pictures. The egg I am using is a silver spangled spitzhauben.

    Definitions you may need:

    Vitteline membrane: The membrane that surrounds the yolk and separates it from the white

    Allantois: The allantois is the chick's connection to the chorion. It helps the embryo exchange gases and deal with liquid waste

    Chorio-allantoic membrane: The chorion and allantois fuse to become this. It is critical in exchanging gases between the embryo and the outside air, and calcium absorption from the egg shell. When the chick hatches, this membrane remains attached to the egg shell.

    Vitellus: The yolk and vitelline membrane.

    Confirmation of Fertility

    I will admit that I did not do this on purpose, but rather dropped an egg on the way to the incubator. Still, it provided a good opportunity to confirm fertility and show what a fertile egg cracked open looks like. You can see that the blastodisc, the small white dot on the yolk of the egg, has been fertilized and has become a blastoderm, indicated by its bullseye-like shape.


    You can see the white dot in the middle and the faint ring around it, indicating that this egg is fertile.

    Day 1

    This is the first 24 hours the egg is in the incubator.


    While there is not much to see yet, there is still activity going on inside. Very soon after incubation begins, a group of cells becomes what is called the primitive streak, and it is the longitudinal axis of the embryo. From this, the head and the backbone of the embryo begin to develop. The nervous system is starting to form. The alimentary tract appears. Blood islands form.

    Day 2

    Hours 24 to 48.


    Still not a lot to see, but inside the embryo is busy developing. The blood islands start linking and forming the vascular system and fine blood vessels appear, and the heart is being formed elsewhere. By the 44th hour of incubation, the heart and vascular system join together. The ear begins to form.

    Day 3

    Hours 48 to 72. Now there is more to see!


    Can you see the embryo in this picture? If not, here is an edited version that is easier to see.


    On this day, the embryo is laying on its left side. The heart is now beating. Blood circulation begins. Limb buds are forming. The nose has begun. The blood vessels are thickening and lengthening, as you can see in the picture above. The allantois begins to form. The vitelline membrane spreads over the yolk's surface.

    Day 4

    Hours 72 to 96


    You can really see the embryo now. A little photo editing to see the details easier.


    The amniotic cavity has developed, which will surround the embryo and protect it, while also allowing it to move. The tongue has started to develop. Blood vessels continue to thicken and lengthen, and the allantoic vesicle appears, which is critical in respiration, waste storage, and calcium resorption. The brain divides into four parts and the eyes are starting to form.

    Day 5

    Hours 96 to 120


    The embryo is clearly visible. Photo editing for details.


    The embryo's head and tail have come closer together, forming a distinct C shape. The fingers on the inferior limbs differentiate. This day is very important - it's when sex differentiation occurs. The respective reproductive organs for each gender begin to form.

    Day 6

    Hours 120 to 144


    The dark spot on the embryo is the eye, you can just make it out.


    The beak has begun to form. The vitelline membrane continues to grow and is now surrounding more than half the yolk. Fissura (small clefts) form between the second and third fingers of the lower limbs, and between the first, second and third fingers of the upper limbs. The eye is much more prominent, as are the heart and brain. Voluntary movement begins; the embryo can now move at will.

    Day 7

    Hours 144 to 168


    The eye is now clearly visible.


    The embryo's neck thins out and now clearly separates the head from the body. The beak is getting larger. The brain starts to enter the cephalic region and now begins to get smaller proportionally to the embryo's size. The comb starts to develop.

    Day 8

    Hours 168 to 192


    No more photo editing; the embryo is now deeper in the egg and there are no more small details to highlight.

    Inside, the embryo's upper and lower beak are now completely differentiated. So are its legs and wings. The neck continues to lengthen. The brain has now settled completely into its cavity. The external opening of the ear has formed.

    Day 9

    Hours 192 to 216


    Claws appear and begin to grow. The allantois grows larger. Vascularization increases. The very first feather follicles are appearing. It's really starting to look like a chick!

    Day 10

    Hours 216 to 240


    The beak is starting to harden and the egg tooth appears. The nostrils become present as narrow openings. The eyelids begin to grow over the eyes. The distal portions of the limbs lengthen. The vitelline membrane now completely surrounds the yolk. Feather follicles now cover parts of the limbs. The egg tooth begins to form.

    Day 11

    Hours 240 to 264

    More than halfway there!


    The eyelids are growing larger and covering more of the eyes. The allantois has reached its maximum size. The vitellus is beginning to shrink. The comb is now more prominent and is clearly serrated. Tail feathers have begun to appear.

    Day 12

    Hours 264 to 288


    Feather follicles surround the opening of the ear. The eyelids continue to grow and are closer to covering the entire eye. The toes have now fully formed.

    Day 13


    The allantois shrinks to join the chorion and become the chorio-allantoic membrane. Scales appear on the legs and toenails form.

    Day 14


    Down now covers the whole body and is growing rapidly. The embryo turns it head towards the blunt end of the egg and gets into a suitable position for hatching.

    Day 15


    The chick is now mostly formed and there are few morphological changes. Down is growing larger and is continuing to grow, as is the embryo. The shrinking of the vitellus accelerates. The embryo begins to position its head under its right wing, which is the pipping position.

    Day 16


    The embryo continues to grow and assume the pipping position. Albumen continues to be absorbed. It's really taking up a lot of the egg now and most of the egg will look black upon candling.

    Day 17


    The embryo's renal system produces urates. The beak, now under the right wing, points to the air cell. The albumen is now fully absorbed.

    Day 18


    "Lockdown" day, when we stop turning the eggs and boost humidity. The chick starts to absorb the vitellus. There is a reduction in the amount of amniotic fluid.

    Day 19


    The vitellus is being absorbed more rapidly. The beak is against the air cell, ready to pierce it and internally pip.

    Day 20


    We have an internal pip!


    The chick has pierced the internal membrane and pipped into the air cell. It is now breathing air. Some gas exchange can happen through the egg shell, which is porous, giving the chick time to finish absorbing the vitellus. Vitellus absorption (usually) is completed on this day. External pipping may also occur.


    Day 21

    The chick inside the egg turns and starts to break the shell in a circle around the top, known as zipping.

    (This picture is of a different egg because my original egg decided to hatch overnight.)


    The chick will push against the top of the egg until the cap pops off and it is free. A little drying later and it is ready for the brooder.

    Here's our chick after 21 days of incubation and development:


    Further Reading

    If you'd like to learn how to build a candler so you can candle your own eggs, there is a build guide on how to make one here. There are also recommendations for candlers you can buy here and here. Dark brown, green, and blue eggs can be hard to candle, so you may want to read about how people have candled their darker eggs here if you are currently dealing with the same issue.

    Good luck and happy candling!

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Recent User Reviews

  1. ChickensAndYoga
    "Wonderfully detailed!"
    5/5, 5 out of 5, reviewed Sep 15, 2018
    Thank you!!
    Pyxis likes this.
  2. -BirdWhisperer-
    "Informative is an understatement...Great Job!"
    5/5, 5 out of 5, reviewed Sep 9, 2018
    This was excellently documented and displayed.. great Job!!
    Miss Lydia and Pyxis like this.
  3. Twoleggedmotherhen
    "Very interesting and informative"
    5/5, 5 out of 5, reviewed Jul 26, 2018
    Was very interesting and informative. I don't plan on hatching eggs, but never say never. If I do can reference this article.
    HeiHeisMom, Bonniebooboo and Pyxis like this.


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  1. lmdengler
    This was great!
      Pyxis likes this.
  2. KathieMc
    I'm hatching my first two clutches of eggs (under a broody and incubator) and this article is exactly what I needed for a better understanding of what to look for. The pictures posted are great...really love the one showing the chicks beak and the information is very detailed!
      Pyxis and (deleted member) like this.
  3. Hybridchucks
    AWESOME article!
      Pyxis likes this.
  4. ChickenyChickeny
    Thanks so much for this article :thumbsup
      Pyxis likes this.
  6. casportpony
    Excellent article. Well written and the pictures are superb!
      Bonniebooboo, Hybridchucks and Pyxis like this.
  7. Bonniebooboo
    Excellent! love the article, pictures, and all the time you put into doing this. Thank you!
      Hybridchucks and Pyxis like this.
  8. N F C
    Always miraculous, thanks for sharing your photos!
  9. oregonkat
    Beautiful article. Precise, well written and the photography is great.
  10. Leaguinea
    How much slower is the development of Guineas seeing as their incubation is 28 days?
      Pyxis likes this.
    1. Pyxis
      Since they're about a week behind, it takes longer to be able to do the first candle - I can usually start seeing life in them by about five or six days.
      Leaguinea likes this.
  11. MagpieDucks
    Excellent as always! You should do one for a duck now!
      Pyxis likes this.
  12. Gramma Chick
    How Rude of that chick to hatch at night !
      ViolinPlayer123 and Pyxis like this.
  13. Miss Lydia
  14. chippy99th
    This article is AWESOME, thank you!
      Hybridchucks likes this.
  15. Hybridchucks
    WELLDONE! This article is so helpful, keep up the GREAT work! xxx
  16. Pyxis
    Thank you everyone!
  17. Bills vs Beaks
    Very helpful, thank you!
      casportpony likes this.
  18. Eggsakly
    I, too, have my first eggs in the incubator, and these photos and the information contained here are my daily companion. I so appreciate your work here, Pyxis. I candled my eggs early on the 8th day, and sure enough(!), the little embryos looked exactly like they should, eyeballs and all. It was so great to understand what I was seeing.
  19. MollySunshine
    This is amazing! Thanks for sharing.
  20. AnneInTheBurbs
    Thanks for these great pictures and details! I have my first eggs in the incubator now, and it's so amazing to see how fast they develop.
  21. FeatherMtnFarms
    Awesome! Great information!
  22. N F C
    Terrific article Pyxis, well done!
      casportpony likes this.
  23. Eggsakly
    Excellent article. Thank you so much.
      casportpony likes this.
  24. room onthebroom
    That was so cool! Thanks!
      casportpony likes this.
  25. WVduckchick
    Fabulous job Pyxis!!
      casportpony likes this.
  26. boskelli1571
    well done Pyxis - very helpful & fascinating!
      casportpony likes this.
  27. shelbyw
    Thanks Pyxis Can't wait to do this !
      casportpony likes this.
  28. shelbyw
    Thanks Pyxis Can't wait to do this !
      casportpony likes this.
  29. katsdar
    Thumbs up great job
      casportpony likes this.
  30. Lady of McCamley
    Nicely done. Really helps show what can be seen with a flashlight and then informed as to what is happening inside that can't be seen.
      casportpony likes this.
  31. Pyxis
    shelbyw - The optimum temperature for storing eggs is actually 60 degrees, so the temps you are collecting them at are fine. You can then store them for up to ten days without them losing viability and hatch them, so your plan is fine.

    There's no way to tell fertility aside from cracking them. You'll just have to candle them after a few days to check if they are developing.
      casportpony likes this.
  32. shelbyw
    I am planning on hatching some baby chickens pretty soon, but every time I gather the eggs they are somewhat cold. the temperature differs from 50 degrees F to about 65 degrees F during the day. I plan on gathering some next week since the weather will be more sunny. Will the eggs hatch if I keep them at room temperature overnight and put them in the incubator that morning? Also is there a way I can tell if my roo is fertilising the eggs other than cracking them? I have seen a blastoderm on the ones that I have cracked before.
      casportpony likes this.
  33. JarrodnJojo2016
  34. Egg - Static
    Wonderful! Thanks for sharing!
      casportpony likes this.
  35. Emslilflock
    Very helpful! Thank you!
      casportpony likes this.
  36. BluRoo Farm OH
    Wonderfully done! Thank you!
      casportpony likes this.
  37. Texas Kiki
      casportpony likes this.
  38. RodNTN
    Wonderful :)
      casportpony likes this.
  39. cluckcluckgirl
    Great job!
      casportpony likes this.
  40. Pork Pie
    Very informative
      casportpony likes this.
  41. Pyxis
    Thanks everyone! I have added up to day 10 now.
      casportpony likes this.
  42. mustangrooster
    This is great!
      casportpony likes this.
  43. BantyChooks
    Lovely images!
      casportpony likes this.
  44. TheKindaFarmGal
    Great article, Pyxis. I look forward to watching it develop!
      casportpony likes this.

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