There have been few analyses of the fat, protein and carbohydrate fractions in zooplankton, and owing to the difficulty of sorting large numbers of single species, the majority of the earlier determinations were necessarily carried out on mixed zooplankton hauls (Brandt, 1898; Brandt & Raben, 1919; Moberg, 1926; Wimpenny, 1929; Drummond & Gunther, 1934; Vinogradov, 1953). Most of these analyses suggested a relatively high protein and fat content, and this was confirmed by Orr (1934 a), who investigated the chemical composition of a single species, Calanus finmarchicus. Orr's result gave fat, protein and chitin as 20–40,35–50 and 3%, respectively of dry weight. Similar high values were also reported by Orr (1934 b) for Euchaeta norvegica. The carbohydrate content was not, however, estimated in either of Orr's investigations since large numbers of animals would have been required. Brandt (1898), after analysing mixed plankton hauls which were predominantly copepods, suggested a carbohydrate content of ca. 20%.