Using dark phase contrast microscopy, prohemocytes, plasmatocytes, granular hemocytes, and oenocytoids in fresh unfixed hemolymph from an appendage of Rhodnius can be sharply distinguished in thin coverslip films. Only the prohemocytes were seen in mitotic division. Plasmatocytes occurred as non-vacuolated and vacuolated varieties. Granular hemocytes were present in 2 distinctive forms those which do not rapidly break down and those which quickly lyse in vitro. Lysis can be prevented by collecting the hemolymph into 0.75% Versene. Large plasmatocyte-like hemocytes which engulf 2 or more granular hemocytes are termed "granulocytophagous cells." Cells which were identified as oenocytoids occurred in 2 distinctive forms: small ones without special cytoplasmic inclusions and larger ones with long filamentous inclusions. In unfixed hemolymph films, circulating hemocytes did not enlarge or suddenly vacuolate at any one period during either the 4th or 5th stadia, and hence, no correlation could be made between swelling and vacuolation of these hemocytes with the secretion of the thoracic gland hormone.