Fig. 6. Age-dependent increase in the number of mitotically-active progenitors of the third wave. Single pulses of radiolabeled thymidine, 1 hour long, were delivered to embryos at different stages followed by immediate fixation. The number of cells with thymidine-positive grains over nuclei was scored per myotome, as described in Materials and Methods. Results represent the mean±s.d. of seven to 14 cervical myotomes per experimental point.

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