At this stage, the embryos can be fixed to be processed for many different purposes, including whole mounts, histology, immunocytochemistry, in situ hybridization, and others. The type of fixative used will depend on the further treatment. It is important not to bring the rings and the watch glasses into contact with any fixative to be used. It saves lengthy cleansing processes, which are unpleasant, time-consuming, and not always a great success.
Place the ring with the embryo in a Petri dish of leftover Howard's Ringer or Pannett and Compton solution from the day before, and wash off unwanted albumin and yolk particles. Either peel the blastoderm away from the vitelline membrane along its peripheral edge and stretch out on a piece of thin plastic (Melinex or overhead projection foil is very good) cut into small squares before immersing in fixative, or just cut the embryo out and transport on a spatula to fixative. Embryos not supported tend to curl up, fold, or distort, and are much more difficult to analyze.
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