As a result of the demonstration of the presence of insulin in mammalian pancreas arid its production for clinical use, renewed interest has been taken in certain glands of the bony fishes which Diamare and Laguesse and later Rennie considered to be homologous with the islets of Langerhans. By the use of the modern cytological methods developed by R. R.
Bensley, Lane, and others, Slater Jackson has demonstrated that these glands which may be called principal islets, a name suggested for the larger of them by Rennie, contain cells having the same characteristics as the cells of the mammalian islets, a i d lllacleod has shown that very large yields of iiisuliii can readily be prepared from them, although these are insignificant or absent from the paiicreatic tissue itself. AIcCormick and Soble have further investigated this source of insulin, and the first-mentioned worker has also described the exact position of the islets in a large series of fishes. Ti1 coiinection with this work islets removed from each type of fish were preserved, after fixation, in 80 per cent alcohol, for microscopic examination, and the findings will be reported later. The present report is confined to a description of the various islet cells in one species of Teleost, the gray snapper (Neomaeiiis griseus), the tissues from which were fixed by Zenker 's solution modified as recommended by Martin, and stairicd by a neutral stain which is a modificatioii 57