Induction and differentiation of an epithelial tumour in the newt (Triturus cristatus).

W A D D I N G T O N (1935) and later Needham (1936) have suggested that the autonomy of tumours originates in a 'morphological escape' of tumour cells from the controlling influence of an individuation field which has locally become weak or has vanished. The persistence and strength of such an individuation field can be seen in its ability to induce its parts to regeneration (Ruben, 1955). This theory might be supported by the observation that in animals which are capable of regeneration, spontaneous tumours are rarely observed. Gersch (1951) compiled a list of all reports of spontaneous tumours throughout the whole animal kingdom and noted that in animals which regenerate well spontaneous tumour occurrence was low. Waddington and Needham suggested that degraded, that is 'escaped' cells, might be brought under control again if they were exposed to the influence of a particularly strong individuation field, e.g. the regeneration field of a regenerating urodele limb. The first experimental attempts to examine these speculations were performed by Rose & Wallingford (1948). They implanted anuran cancer (Lucke carcinoma of Rana pipiens) into regeneration blastemata of limbs of adult Triturus viridescens. The authors described differentiation of the tumour cells into cartilage, muscle, and connective-tissue cells. Although these results seem to support the speculation of Waddington and Needham, no definite evidence could be given that the differentiated cells were actually the Rana cells. The only available difference used to distinguish Rana and Triturus cells was the smaller size of Rana nuclei. Ruben (1955, 1956) implanted the same carcinoma into limb regeneration blastemata of Amblystoma larvae and adult T. viridescens and could not observe any alteration of the tumour tissue except degeneration. In both of these previous experimental attempts the method used does not seem to be adequate to permit definite statements. There was always a foreign