Embryonic Development in the Chick
Aristotle was the first to view the development of the chick embryo and report the steps of its development. Because all chordate animals follow similar patterns of early development, viewing the chick embryo has much to teach about development of higher chordates, such as in humans. It is especially informative to compare a 40-48 hour embryo with a 70-72 hour embryo. The earlier show the primative three part brain, neurulation in progress, fewer somites, the heart is not beating yet, and the embryo is still linear. The 72 hour embryo has a 5 part brain, a beating heart, many somites, limb buds and it has arched and twisted, all in only 24 hours.
Here is a page devoted specifically to the embryonic development of the brain.
Equipment
petri dish, 39 C
small three cornered file (sharp)
scalpel
tweezers, preferably with curved tips
dissection scope and lamp (strictly follow carrying instructions!)
iris scissors (they have curved blades)
depression slide, 39 C
(or microscope slide with wax pencil drawn circle to contain solution)
Supplies
fertile eggs, incubated at 39 C for 72 hrs
(A few at 33 and 48 hrs are instructive, but because the embryos are smaller, they are more difficult to handle)
39 C Ringer’s solution * in dropper bottle (or other isotonic solution)
Whatman #1 filter paper (or other)
See also: Abraham & Thomson, Lab Outlines in Bio III, 247-257, (~1975).
1. Collect equipment at your desk:
dissection scope and lamp (make two trips, use two hands for each trip)
dissection kit
iris scissors
And, all at 39C:
Ringer’s solution
depression slide
petri dish bottom (or top)
Cut a ring of filter paper, size of a quarter with a 5/8 hole which will encircle the embryo.
2. Pick up an egg from the incubator, keeping egg in same orientation as in incubator and keep it warm with a lamp close to its surface.
With a pencil, mark a circle 3/8th inch bigger diameter than a quarter on upper surface of egg.
Place the egg in petri dish with paper towel cushion underneath. Gently score with a file around the circle with repeated long slow strokes. Do not press hard, or egg will break.
3. With scalpel and/or tweezers, flick off the shell inside the circle, trying not to break inner shell membrane.
It is not necessary to flick all of the shell off, but you need room to cut the shell membrane in the next step.
4. With iris scissors, make shallow cuts to cut inner shell membrane close to shell. The yolk will be floating near the surface with the embryo on top. Be careful not to pierce the vitelline membrane which surrounds and contains the yolk, or else you will obscure the operation with yolk. Flake off additional shell if more clearance is needed. The embryo should be float in the center top.
5. Carefully place filter paper circle so that it encircles the embryo (still floating in the center of the opened egg, at the top?). Trim paper if necessary before putting it in place.
(In this image, the egg has broken into the petri dish, but the embryo is still visible.)
6. Carefully cut vitelline membrane just outside of the filter paper to free the assembly. Do not press down or the assembly may sink and be lost in yolk.
(Poke down with one blade, lift up slightly, cut the membrane.)
7) Pre fill a warmed depression slide with warmed Ringer’s solution to receive the embryo.
When cut free, carefully grasp with tweezers both the membrane and paper along the edge of the assembly.
Pick up the assembly and gently flush off yolk the underside with Ringers solution.
Transfer to a warm depression slide filled with Ringer’s solution. Make sure that the embryo does not become detached, nor is not covered by the embryonic membranes or filter paper. Keep it alive by keeping warm and moistened with Ringer’s at all times.
8. Examine under the dissecting scope. Illustrate the embryo according to the hours of incubation. The beating heart seen in older embryos will continue for some time providing that it is kept warm and wet with Ringer’s solution. Draw the embryos in chronological order to show the stages of development as seen at hours 48 and 72.
Include and label:
forebrain (prosencephalon: telencephalon and diencephalon)
midbrain (mesencephalon)
hindbrain (rhombencephalon : metencephalon and myelencephalon)
optic cup
lens placode
nose rudiment
auditory vesicle
pharyngeal arches (also called gill slits)
vitelline arteries and veins
neural tube (or neural grove seen in early embryo)
heart atrium
heart ventricle
somites
wing “buds”
leg “buds”
Here is a labeled view of a 40 hour chick embryo (about 10 somite stage).
Here is a labeled view of a 72 hour chick embryo.
Here is a labeled image of a prepared slide of a chick embryo.)
9. Clean and dry all equipment before putting away to prevent corrosion, especially the metal utensils. Note than any egg remaining will dry and be very difficult to clean off later
*Ringer’s Solution:
Calcium chloride 0.1 g
Glucose 1.0 g
Potassium chloride 0.1 g
Sodium bicarbonate 0.2 g
Sodium chloride 6.5 g distilled H2O, q.s: 1 L
Images taken in 2005.
Images taken in 2008.
Other pictures
1. Experimenter holds meter stick with 50 cm mark on line of card, zero end of stick down. Be careful to line up the ruler exactly on the 50.0 cm mark. (The experiment can be done with a yard stick with a little additional conversion, and using a different equation for inches.)
5. Experimenter reads the position of the line on the ruler to the nearest tenth of a centimeter (66.0 cm in the image to the left), subtracts 50 cm from that to get the distance the ruler dropped , and records the data in the notebook in cm (16.0 cm dropped in this example). Repeat at least five times to determine an accurate average. (You may drop the fastest and slowest reactions to see how that affects it)
David Fankhauser 
