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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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