1. Explantation experiments of pharyngeal endoderm, alone or together with various ecto- or endomesodermal materials, within epidermal envelopes were performed, using the neurulae of Trituras pyrrhogaster and Hynobius nebulosus as materials.

  2. The piece of endoderm, when explanted alone within the envelope, did not differentiate into any definable structure, persisting as an amorphous mass of undifferentiated endodermal cells, even after a prolonged cultivation as long as 30-40 days. Typically differentiated endodermal structures were found only in the explants in which the endodermal piece was combined with the ecto- or endomesodermal materials.

  3. When the pharyngeal primordium was explanted together with the material of either neural fold or archenteric roof, irrespective of the regions from which these materials were removed, the production of pharynx always occurred.

  4. When combined with lateral plate mesoderm, the pharyngeal primordium generally developed into an intestinal vesicle. Oesophagus, stomach, liver, or pancreas was occasionally found in these combination explants.

  5. Some xenoplastic explantations, in which the pharyngeal rudiment of Hynobius was combined with ecto- or endomesodermal material from the neurula of Rana japónica, were also carried out. Hynobius endoderm showed differentiation into pharynx when combined with anterior neural material of Rana, but it produced an intestinal vesicle when lateral plate of Rana was included.

  6. In all the available specimens of the present experiments it was a rule that pharyngeal differentiation occurred within free mesenchyme, while intestinal structures were found to be surrounded by endothelial tissue.

  7. On the basis of above data it is concluded that the pharyngeal primordium is still pluripotent in the early neurula stage, and its future fate may be varied, depending mainly upon the sort of connective tissue which is present around it.

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