The anatomy and histology of the alimentary canal is described in H. carpio (Kramer, 1881) . Histochemical methods have revealed extensive enzyme activity in the midgut cells and lumen. In addition, the oesophagus contains acid phosphatase and the wall of the post colon shows strong alkaline phosphatase activity associated with a brush border. The midgut epithelium appears to consist of two main kinds of cell. The stomach wall is composed of cells many of which show strong alkaline phosphatase activity and have microvilli. These are thought to be absorptive in function. The posterior and outer walls of the caeca include large claviform cells with strong esterase activity and there, these cells have a digestive function. Bacteria are found in large numbers in the lumen of the midgut and the mite appears to be a general browser on the zoogloeal film surrounding the medium in se,vage beds. Bacteria are also found in the cells of the midgut wall and may form a mycetome. Intraluminar and intracellular digestion may occur. Although the food bolus lying in the colon shows enzyme activity, the wall of this organ does not appear to be the site for the production of these enzymes. The Malpighian tubules are well developed, have granular contents and appear functional in this species. The nomenclature used by various authors to describe the organs of the alimentary canal in Sarcoptiform mites is reviewed, illustrating a continuing lack of uniformity and confusion. The terminology adopted by Hughes (1950, 1959) is recommended for the gut of the Sarcoptiformes.