chick_embryo

	EMBRYONIC DEVELOPMENT IN THE CHICK ©David B. Fankhauser, Ph.D., Professor of Biology and Chemistry University of Cincinnati Clermont College, Batavia OH 45103
score a circle for removal of section of shell	This page has been accessed times since 3 June 2003. 7 April 1980, rvsd 28 March 1994, 19 March 1996, 2 April 98, 28 Mar 01, 31 May 01, 24 Mar 02, 3 May 03	40 hour embryo

Equipment	Supplies
petri dish, 39C small three cornered file (sharp) scalpel tweezers, preferably with curved tips dissection scope and lamp iris scissors (they have curved blades) 39C depression slide (or microscope slide with wax pencil drawn circle to contain solution)	fertile eggs, incubated at 39C for 72 hrs (A few at 33 and 48 hrs are instructive) 39C 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.

	1. Cut a ring of filter paper, size of a quarter with a 5/8 hole which will encircle the embryo. Collect equipment at your desk: dissection scope and lamp, dissection kit, iris scissors. And, all 39C: Ringer's solution, depression slide, petri dish bottom (or top). 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.
	2. 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. (Thanks to Angella Pollitt for for taking pictures in sections 2, 3 and 4.)
	3. With scalpel and/or tweezers, flick off the shell inside the circle, trying not to break inner shell membrane.
	4. With iris scissors, 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.
	6. Carefullycut 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, lift and cut.)
	7. When cut free, carefully pick up and transfer the assembly with tweezers, flush off yolk with Ringers, and 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 membranes or filter paper. Keep it alive by keeping warm and moistened with Ringer's at all times.
40 hour embryo: 70 hour embryo: 40hour and 70 hour, same slide	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. Draw the embryos in chronological order to show the stages of development as seen at hours 48 and 72. Label: fore-, mid- and hindbrain, optic cup, lens placode, nose rudiment, auditory vesicle, pharyngeal arches, vitelline veins, neural tube (or neural grove seen in early embryo), atrium, ventricle, somites, wing and leg "buds".
	9. Clean and dry all equipment before putting away to prevent corrosion, especially the metal utensils.