Blood Sugar and the Follicles of Langerhans in the Ammocoete Larva

Abstract

Glandular follicles, first described by Langerhans, develop in the wall of the alimentary canal of the ammocoete larva at the point of junction of fore- and midgut, and have often been compared with the pancreas of higher forms. They have been re-examined histologically, using Helly's fixative and the ‘Azan’ stain, and the view of some recent workers, that they have the appearance of endocrine structures, is confirmed. They comprise only one type of cell, however, which shows no decisive resemblance in staining reaction to any of the cell types characteristic of typical islet tissue. The injection of glucose into ammocoetes usually produces a marked response in these cells, involving extensive vacuolization, while destruction of the follicles by cautery induces a significant rise in blood sugar. These reactions, which imply that the follicles are involved in carbohydrate metabolism, are similar to those associated with the B cells of islet tissue. It is concluded that the evidence, while not yet complete, suggests that the follicles represent a primitive stage in the evolution of the endocrine component of the vertebrate pancreas, and it is pointed out that ‘follicles of Langerhans’ would be an apt designation for them. Further work will be necessary to clarify their relationship to the islets of Langerhans of higher forms.