ABSTRACT The question of the anatomical and functional nature of the islet-like groups of cells occurring within the pancreas of vertebrate animals has been studied by a large number of investigators since attention was first directed to them by Langerhans in 1869. These inquiries have for the most part been confined to the higher vertebrates, and summaries of their results have already been given by other writers (Laguesse, 1894; Oppel, 1900). Notwithstanding the somewhat extensive literature of the subject, there is so much disagreement as to the real nature of these bodies that further inquiry was desirable. Oppel (13) wrote in 1900, “Was die Bedeutung der intertubularen Zellhaufen anlangt, so ist dieselbe, so viel auch daruber geschrieben wurde and so viele Ansichten auch daruber bestehen, noch nicht ganz erklart.”