The Structure and Taxonomic Status of Toddia from the Cottonmouth Snake Agkistrodon piscivorus leucostoma*

SYNOPSIS. Of 163 cottonmouth snakes Agkistrodon piscivorus leucostoma from Louisiana, 4 (2.4%) were infected with Toddia França, 1911, an erythrocytic parasite said to be a protozoon. In the 4 blood films, Toddia had an average size of 1.65–1.98 μ with a total size range of 0.88–3.4 μ. In Giemsa‐stained slides, the organisms were usually a round red‐staining mass which was either homogeneous or sometimes contained granules. A pattern of growth was seen in which the organisms increased in size and in which there was development of an erythrocytic inclusion. The inclusion, which was not a part of the parasite, developed first as a spheroid and then became altered in shape to a crystalloid square, possibly a break‐down product of the host cell hemoglobin. The first noticeable damage to the erythrocytes was to the nuclei, which became nearly round; later, when the crystalloid had formed, the host cell degenerated into a small mass containing a pycnotic nucleus, a remnant of cytoplasm and the Toddia. A review of the literature on Toddia and on Pirhemocyton Chatton & Blanc, 1914 leads to the conclusion that the organisms are closely related and that both are viruses of the DNA type.