Cells of the presumptive forebrain region and axial mesoderm of Triturus neurulae were disaggregated and combined in different ratios. The differentiation of the central nervous systen in these explants was dependent on the relative amount of mesodermal cells present: an increase of mesodermal cells resulted in a corresponding increase in the frequency with which caudal structures of the central nervous system developed and a gradual loss of the forebrain formations.
The ultimobranchial body is a derivate of the pharyngeal cavity which has been found in all vertebrates studied at least at some stage of development. Its origin, development, and structure has been studied in many species but nevertheless nothing certain is known about its significance and activity. Earlier authors have used several terms for this organ, e.g. accessory thyroid gland, lateral thyroid, corpus Y, suprapericardial body, telobranchial body, and postbranchial body. The term mostly used at present, ultimobranchial body, was suggested by Greil (1904).
It is not possible to give a consistent picture of the formation of the ultimobranchial body, since it is evidently different in different vertebrates. In fishes it is formed from the sixth rudimentary visceral pouch (van Bemmelen, 1889); in amphibians Maurer (1888) regards it as being formed from the ventral wall of the pharyngeal cavity, while Greil (1904) derives it from the sixth visceral pouch.
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