EmbryoIntroFIG 5: Embryonic cell lineage.
Vertical axis represents time at 20°C, from 0 min at first cleavage to 800 min at hatching. Many of the observations were made on eggs which were developing at slightly different rates (due to temperature variation and the effect of prolonged illumination); these primary results were normalised, by means of certain prominent cell divisions, to the course of events in eggs which were kept at 20°C and viewed infrequently. The precise times of individual events were not our primary concern, and should not be taken too seriously; the likely error varies from ±10% at the beginning of the lineage to ±2% at 400 min. Horizontal axis represents the direction of cell division. Each terminal branch of the embryonic lineage is labelled either with X (indicating cell death; the position of the X on the time axis indicates the time of maximum refractility) or with a lineage name followed by a functional name. Large arrowheads denote cells which divide postembryonically, and small arrowheads denote nuclei which divide postembryonically, Symbols O and --- link precursors which give rise to bilaterally symmetrical groups of cells, the symbol ~ being included for cases of imperfect symmetry, cord, ventral cord; gang, ganglion; lumb, lumbar; d-r, dorsorectal; p-a, preanal, r-v, retrovesicular; lat neur, isolated neuron lying laterally
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