SYNOPSIS.The filiform microgamete ofHaemoproteus columbaeconsists of an elongate double‐walled nucleus paralleled by 2 axonemes embedded in a homogeneous matrix. At one end of the gamete, the axonemes are sharply flexed back on themselves, but no conventional kinetosome has been recognized. No mitochondria have been seen. Single‐walled vesicles occur in the matrix, and the entire gamete is surrounded by a single membrane.The large round macrogamete has a conspicuous central nucleus with its outer membrane drawn out into anastomosing evaginations which extend to the periphery of the cell. A moderately electron dense material fills the space between the 2 nuclear membranes and the lumina of the evaginations. Nucleolar material may occur in scattered masses within the nucleus. One or 2 axonemes appear to arise endogenously next to the nuclear membrane.The cytoplasm is filled with ribosomes and perhaps glycogen granules. Typical protozoan mitochondria and vesicles containing pigment retained from the erythrocytic stage are found in the peripheral cytoplasm. Accumulations of dense‐walled vesicles occur in the cytoplasm in conjunction with evaginations of the nuclear membrane. Amid these vesicles triple‐ringed discs resembling the cytostomes of merozoites are frequently seen.Several distinct layers of dense material surround the micro