No satisfactory explanation for the absence of the ileocecal portion of the digestive system in the newborns with cloacal exstrophy has been offered previously. This is a report of such a case in which the lymphocytes and plasma cells were used as tissue markers to identify the origin of the lymphatic-rich ileocecal portion of the digestive tract. The absence of these cells, in this case demonstrated immunohistochemically, is suggestive of a dual origin of the midgut. Normal embryogenesis of the digestive system is reviewed and the possibility of participation of the allantois, in addition to the yolk sac, in the embryogenesis of the ileocecal segment of the gastrointestinal tract is discussed.