This study was undertaken in order to clarify the various ideas concerning the relation of the blood supply to the glandular tissues of the pancreas. An embryologic and anatomic consideration of the blood vessels of the pancreas with special reference to their relation to the islands of Langerhans is included. The work on the embryology of these vessels was carried out by a study of serial sections of embryos of the mouse, rat, and man at different stages in their development. The larger vessels and their relation to the pancreas were studied by gross dissection and by the use of celluloid corrosion method. The intrapancreatic circulation was studied after arterial and venous injections with Berlin blue, both in serial sections and thick sections cleared by Spalteholz’s method and by an acute congestion method. Laguesse (18), in 1902, described the vessels as playing an essential part in the early development of the islands of Langerhans. He claimed that the island cells in amphibians first differentiate close to the vessels. Hansemanii in the same year considered that the islands of Langerhans arise with the capillaries from the stroma, the capillaries first widening and the adjacent cells becoming richer in protoplasm, thus forming the glomerular-like structures. He believed that there