The following study grew out of work on the susceptibility of various species of mosquitoes to the avian malarial parasite, Plasmodium elongatum, and its transmission through the mosquito to the canary and the duck. A review of the literature revealed the following references to the sexual forms. P. elongatum was named after its gametocyte (Huff, 1930) which was subsequently found to be confined entirely to erythrocytes and normoblasts in the peripheral blood of the canary (Huff and Bloom, 1935). Manwell (1943) observed that the gametocytes of this species in the duck were frequently smaller than in the canary and were more likely to occupy the polar position of the host cell. Gametocytes represented a large proportion of the parasites seen in the peripheral blood of ducks by Wolfson (1*946) and a single attempt by her to infect Culex pipiens was unsuccessful.