Endoderm/mesoderm multiplication rates in stage 5-12 chick embryos

Multiplication rates for the endoderm/mesoderm layer of the head-process to 17-somite-stage chick embryo were studied by implanting essentially identical transplants labeled with tritiated thymidine into paired recipient embryos. One recipient was fixed as soon as the transplant had healed (after 30 min) and the other was reincubated an additional 3.5 to 22.5 hr; the ratios of labeled cells in the paired embryos provided points on a graph that indicated that doubling of endoderm/mesoderm cells in head-process-stage chick embryos occurs at approximately 4.0 and 17.2 hr of reincubation.