9 Mammalian tumors were first grown successfully on the chorio-allantoic membrane of the chick embryo by Murphy. The recent development of this technique has been surveyed by Karnofsky, et al. The first intraembryonic transplants of normal mouse tissue were performed by Rawles. 10 Bueker2 has combined both techniques: he implanted mouse tumor in the body wall of three-day embryos. This experiment was performed in connection with certain neuro-embryological problems. Previous experiments had shown that the differentiation of primary sensory and motor systems in amphibia and in chick embryos is to a large extent under the control of extrinsic factors. The effect exerted by the periphery is not a speciesspecific; transplantations in Amphibia (Harrison, Detwiler³) had proved the capacity of nerve fibers to invade heteroplastic structures. The same compatibility was demonstrated by Buekerı to exist between nerve fibers of the chick embryo and the peripheral field provided by the guinea hen embryo.