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That the presumptive ectoderm of urodeles may be transformed into
the endoderm by grafting it into the endodermal area was suggested by
Mangold (1923), and Holtfreter (1933b) in heteroplastic or xenoplastic
experiments. However, in these experiments, the stage of fixation of the
host embryo was too early to demonstrate that the graft was really able
to form definitive endodermal tissues. More convincing in this respect
were a few grafting experiments of Raven (1935) in which the host was
reared for a longer time, and attained the stage of differentiation of
F I G . 5. A n endodermal vesicle of intestine type, induced in an ectodermal explant of
the Triturus gastrula with guinea-pig bone marrow. Cultured for 59 days. External to
the intestine epithelium, mesothelium and mesenchyme are formed, χ 2 8 0 (C. Takata).
definitive endodermal tissues. Although the grafting was homoioplastic,
the result showed that it was probable that the grafted ectoderm was
induced to form intestine and liver tissues. Our experiments reviewed
above definitely demonstrate the formation of various endodermal
tissues from the presumptive ectoderm. Probably this striking phenomenon cannot be interpreted as a secondary induction of endodermal
tissues out of the presumptive ectoderm by the mesodermal tissues
primarily induced by the bone marrow, because a combination of the
ectoderm with the mesoderm made under various conditions has never