At the time an egg is laid, the embryo has already undergone cleavage, and gastrulation has just started; it comprises a bilaminar blastoderm of about 60,000 cells. Conveniently, however, if the egg is not incubated, further development is virtually arrested at this stage, but normal development is resumed when the temperature is raised. Unincubated eggs can remain viable for about 7-10 d if stored at room temperature, although the proportion of nonviable embryos will increase during this time. The number of viable embryos is increased by storage of unincubated eggs at 12°C with the air space (blunt end) upward.
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