Cytogenesis of the human fetal pancreas.

The initial survey of pancreatic islet formation in the human fetus was reported by Pearce (’03) who described the development of the islets from the primitive pancreatic tubules. The islets were first identifiable in a 54 mm fetus as clusters of small eosinophilic cells attached to the tubule but following vascularization, as observed in a 90 mm fetus, they became separated from the tubules by an encroachment of connective tissue. Studies by Seyfarth (’20) and Nakamura (’24) confirmed the origin of the islets but differed from Pearce in that they found the first islets in 50 and 80 mm fetuses, respectively. The occurrence of two cell types in the fetal islet was initially reported by Weichselbaum and Kryle (’09) while Kardasewitch (’27) described two cell types within the duct system of a 45 mm fetus. The first indication of islet development was noted by Kardasewitch in a 60 mm fetus when small darkly stained cells, the “Insulocytes,” began to proliferate but “typical” islets were not observed until the 90 mm stage. Neubert (’27) also described the development of islet cells from ductule epithelium and, in addition, from cells located at the terminal ends of the ducts. These cells contained intensely stained granules and exhibited a “muddy” appearance which was typical of all young islet cells. Furthermore, such scattered isletpotential cells were always found on the outer surface of groups of cells arranged around adjacent blood vessels, a grouping referred to by Neubert as an “Inselfeld.” In a more recent study of the fetal pancreas, Ferner and Stoeckenius (’51) divided islet development into three stages : (a) single cells, (b) “Inselfeld,” and (c) “Mantelinsel.” The first stage, observed in a 130 mm fetus, consisted of alpha cells within the walls and terminal procy , University of Michigan, Ann Arbor, Michigan