The organization of thcl urodele limb regenerate is characterizrd by c2 strict ~orre.jpoii~leiice, suggesting a causal relationship, betwc-c.en tlic components of the regenerate and their eonnterparts in the stump. This is most rtrikingly illustrated hy the direct contiiiuity of the old arid the new skeletal elements. lriasiiiuch a s the skeleton is the first tisbue to differentiate in a developing lhstenia, and since bone can be subjected with facility to various experimental techniques, the present account represents a n inquiry into the factors rcsponsiblc for the liistogcriesis of cartilage, with particular reference to the role of bone in this p-ocess.Notwithslanding the spatial, arid perhaps c a u d , relatioilship between corresponding skeletal elements in tlic stiinip and the regenerate, there is considerable evidence that other factors are also involved, for iiuinerous investigators have described normal skeletal regeneration f r o m limbs partially or entirely deprived of ihcir skeletal elements. Extirpation of one of the two bones in t l i c h lower extremity, followed hy amputation through the operat ed region, results in normal reconstitution of the lost parts including regeneration of the