Light and electron microscopic study of crocodile islets of Langerhans.

The tissue of the islets of Langerhans was studied in Alligator mississippiensis and Caiman niger. The distribution of the insular tissue in the pancreas was described from the picture in the light microscope, together with the incidence of characteristic islets, which frequently surround the duct tress, and of scattered insular cells. Five types of endocrine cells, distinguishable by their staining properties and typical electron microscopic image, were described in the insular tissue. In addition to A-, B- and D-cells, others which very probably correspond to EC- and PP-cells are described. Mixed cells were also found. The pancreatic interstitial connective tissue contains large numbers of nerve fibre bundles; isolated nerve fibres may penetrate to the insular cells. At the site of contact of a nerve ending with an endocrine cell, characteristic thickening of the membranes is sometimes found.