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in the pharynx and converge into the
dorsal aorta. The heart has begun to differentiate into an
atrium and a ventricle.
72-hour.The
flexure of the embryo is now pronounced and the embryo is
lying on
its left side. The brain has
further subdivided and the olfactory pit (nose) is
present over the tip of the
forebrain. The lens of the eye should be visible.
Lateral swellings
representing the limb buds and a curved tail are also
present.
Living embryos
1.
Isolate a living 3- to 6-day chick embryo. Obtain an egg and
clean scissors, forceps, a plastic spoon. First prepare a
small petri dish
withHoward
Ringer's solution.
Gently rotate egg, clean with 70% ethanol and set down for a
few minutes to allow the embryo to float to the top. Open up
the blunt end of the shell and carefully peel back the shell
membranes. Observe the embryo under the dissecting
scope.
2.
Measure the heart rate and observe any other movement. Grab
the outer ring of the blastodisc near embryo with fine
forceps in your non-cutting hand. Try not to pinch any blood
vessels. Quickly cut around embryo.
3.
Keeping hold of the embryo with the forceps, pick up a
plastic spoon with your cutting hand and slide it under the
embryo. Continue to hold onto embyo, lift with the spoon and
transfer to the petri dish filled with Howard's and examine
with the dissecting microscope. have your lab partner stand
by with scissors in case the embryo wasn't completely
detached. If the dish is cloudy with yolk, transfer embryo
to a fresh dish of Howard's.
Note: an alternate method of embryo isolation is to
break the egg open into a finger bowl of Howard's. This is
similar to cracking an egg for culinary purposes, but the
yolks of warm eggs are more fragile than those of
refrigerated ones. First, place the egg in a horizontal
position to allow the embryo to float to one side. Next,
keeping the same orientation, crack the egg gently against
the side of a finger bowl filled with Howard's. Submerge the
egg and gently pull the ends appart to crack the egg
open.
Instructor's
prep list
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