Incorporation of thymidine-3H into the activated sea urchin egg with special reference to subthreshold stimulation with an activating reagent

It was ascertained that thymidine-³H added exogenously is incorporated periodically into the nucleus of the fertilized and the artificially activated eggs of Pseudocentrotus, Temnopleurus and Anthocidaris. Eggs stimulated insufficiently with butyric acid did not show any enhancement of incorporation of thymidine-³H. However, repetition of an insufficient stimulation induced incorporation of thymidine to some degree, although no visible cortical changes occurred.