Onto- and phylogenetical aspects on insulin-producing islet-cell tumors.

When onto- and phylogenetical aspects are taken into account when studying insulin-producing islet-cell tumors, it becomes clear that the recently discovered "type IV" islet parenchymal cells (or "delta 1" -cells) may play an important role in various states of hypoglycemia, both of neoplastic and non-neoplastic origin. Moreover, it becomes obvious that increased attention to this kind of islet cell through intensified light-microscopical, histochemical, ultrastructural and experimental investigations covering a wide range of animals, may help to clarify several unsolved problems in the cytological composition of the islets of Langerhans. The occurrence of islet-cell tumors (or hamartomas) in the most primitive vertebrate islet parenchyma known, viz. that of the hagfish, Myxine glutinosa, is reported, as well as an additional case of mixed carcinoid-islet-cell tumor in a human pancreas.