1. With only a little experience, early embryos can be staged by observation through a dissecting microscope using transmitted light alone. At stages following the onset of somitogenesis, staining is not required for staging, which only requires observation with reference to refs. 2 and 3.
2. This works well for embryos with up to 3 d of incubation, but the filter paper cannot hold the weight of older embryos—these should be simply cut out using the method in Subheading 3.3.1., hand-washed and transferred to fix using a spatula.
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