In Pediculus humanus are found two groups of excretory-accumulatory cells known as nephrocytes.The one group, the peri-oesophageal, lies ventrally and consists of large cells aggregated usually in two masses about the oesophagus anterior to the reniform salivary glands.The second group lies dorsally and consists of disseminated cell aggregates linked with the fat body.The typical nephrocyte is a binucleate cell with granular protoplasm containing greenish droplets of varying size. The excretory function of the nephrocytes is demonstrated by intra-coelomic injection of ammonia-carmine. The latter, 24 hours after injection, is taken up by the nephrocytes which become red and filled with the carmine granules. These granules remain in the protoplasm of the nephrocytes throughout the life of the insect.Similar cells exist in Mallophaga and have been wrongly described by some authors as salivary glands.The two groups of nephrocytes, described by us in Pediculus, occur in other insects, but the dorsal group in the latter forms usually two chains of cells (known as pericardial cells) lying on either side of the heart.