Two sites produce enzymes in the midgut - the pancreas and the intestinal wall. The intestinal wall is folded or ridged in simple patterns which can be species specific. Secretory cells for both mucus and all three classes of enzymes develop in the depths of the folds, migrate to tops of the ridges (closest to the gut lumen), and then discharge their products. The pancreatic cells produce enzymes and an alkaline solution which are delivered to the upper midgut through the common bile duct. The control of pancreatic secretions (and the pyloric sphincter) in fish is probably the same as in mammals, but there is no information on teleosts yet.