Quantitative measurement of active polysomes of developing chick muscle

The hatching process in embryos of the toad Xenopus laevis consists of two temporally distinct phases. In phase 1, the embryo escapes sequentially from the two outermost jelly layers, J₃ and J₂, and during phase 2 the embryo hatches from the last remaining jelly coat layer J₁ and the fertilization envelope. Phase 1 hatching appears to be a physical process caused by water inbibition of jelly coat layer J₁ and dynamic changes in the volume enclosed by the fertilization envelope. The combined turgor pressure ruptures jelly coat layers J₃ and J₂. The subsequent phase 2 hatching is a result of both physical and chemical processes. Phase 1 hatching exposes layer J₁ to the medium which, in contrast to jelly layers J₂ and J₃ is partially soluble, and permits its gradual dissolution during Phase 2. The embryo secretes a proteolytic enzyme from the frontal region which partially digests the fertilization envelope; subsequent embryo movement ruptures the weakened envelope and completes the hatching process.