[Development of the pancreas of the urodele amphibian, Pleurodeles waltlii (Michah). A morphologic and ultrastructural study in vivo].

The study of the pancreas development in Pleurodeles waltlii Michah (amphibian urodele) shows the following characteristics: 1) The dorsal rudiment is formed the first, even before the irrigation of the tree producing branchial buds (end of stage 30). This rudiment is formed by isolation of cells rich in vitellus from the dorsal wall of the archenteron. The ventral rudiment, which is massive and more developed on the right side than on the left, appears only a few hours later. The two rudiments fuse at the eclosion time (after stage 35). (2) The elements of the exocrine pancreas, which are the first formed, take place little before the eclosion (stage 33b). They come from the transformation of the cells rich in vitellus, with embryonic character. Solid masses of these cells are first formed and then hollowed in tubules which secondarily join the central pancreatic canal of rudiments. (3) The endocrine elements, which are as rare in the larva as in the adult, appear only after the eclosion. The B cells are formed first (stage 35).