On the development of the hypophysis in the tailed amphibia, especially of Diemyctylus pyrrhogaster and the movement of the pars anterior

Although the literature dealing with the development of the hypophysis is voluminous, there is still a great deal of confusion concerning the cradle of the anlage of the epithelial hypophysis. An endless chain of discussion has been evoked by the question as to whether the epithelial hypophysis is derived from the entoderm or from the ectoderm, or whether it is a compound of elements derived from both of these germ layers. On account of these discrepancies the author previously undertook an investigation on the development of the hypophysis of Rhacophorus schlegelii and published the results. For the purpose of comparing with the previous results, recently the author investigated the development of the hypophysis of Diemyctylus pyrrhogaster. From the results of my experiments, the following summary and conclusions were made:1) The epithelial anlage of the hypophysis of Diemyctylus pyrrhogaster as well as that of Rhacophorus schlegelii develops from the inner layer of the dorsal wall of the stomodaeal invagination which consists of the ectoderm. The foregut or the notochord plays no part in the development of the hypophysis.2) The hypophysis consists of three epithelial lobes and a neural lobe. The epithelial hypophysis develops from the epithelial anlage of the hypophysis which is derived from the inner layer of the dorsal wall of the stomodaeal invagination and it consists of the pars anterior, the pars intermedia, and the pars tuberalis.3) The pars anterior of Diemyctylus pyrrhogaster as well as that of Rhacophorus schlegelii develops from the main central portion of the epithelial anlage and it consists of the asidophil cells and the basophil cells and in the larvel stage it has no blood-vessel but in adult it has many blood-vessels. The pars anterior of adult Diemyctylus pyrrhogaster is like a convex lens and it lies caudal and ventral to the other lobe and sits on the sella turcica. Owing to the pressure of the expansion of the infundibulum, the pars anterior moves caudally so that in the larval stage of Diemyctylus pyrrhogaster the main portion of the pars anterior lies in contact with the infundibulum but in adult only a cranial part of it is attached to the infundibulum.4) The pars intermedia of Diemyctylus pyrrhogaster as well as that of Rhacophorus schlegelii develops from the dorso-caudal portion of the epithelial anlage and it consits of the basophil cells and in adult it contains the kolloidmass but it has no blood-vessel. In the larval stage of Diemyctylus pyrrhogaster the pars iutermedia lies dorsal to the caudal portion of the pars anterior but in adult it lies to the middle portion of the pars anterior and its cranial portion connects with the pars neuralis.5) A pair of the pars tuberalis arises from the pars laterlis which developed from the crauio-lateral portion of the pars anterior and it consists of the basophil cells but it has no blood-vessel. In the early stages a pair of the pars tuberalis of Rhacophorus schlegelii connects with the pars anterior but later on becomes detached, forming two epithelial disks lying close under the ventral wall of the infundibulum. A pair of the pars tuberalis of Diemyctylus pyrrhogaster is the long proces in shape and these processes do not become detached from the pars anterior as in the former, but maintain their connections with the pars anterior throughout life.6) The pars neuralis of Diemyctylus pyrrhogaster as well as that of Rhacophorus schlegelii develops from the caudal tip of the infundibulum and it consists of the nervefibres, the connectivetissuefibres, the ependym-cells and many blood-vessels. It lies cranio-dorsal to the pars intermedia and intimately connects with the pars intermedia.7) As to the order of develoment of the various lobes of the hypophysis, at first the pars anterior and the pars intermedia develop at the same time, then the pars tuberalis appears, and lastly the pars neuralis appeirs.

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