An Ultrastructural Study of First‐ and Second‐Generation Merogony in the Coccidian Sarcocystis tenella1

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Abstract
Sporocysts of the coccidian S. tenella were originally isolated in the feces of a coyote. Sporocysts used for inoculation of lambs were obtained from experimentally infected dogs. At 14, 16 and 19 days postinoculation (DPI) of lambs with the sporocysts, various developmental stages of 1st-generation meronts were found within cells located between the endothelium and internal elastic membrane of mesenteric arteries. At 19, 21 and 25 DPI, 2nd-generation merogony occurred in cells associated with capillaries and arterioles of kidney glomeruli and convoluted tubules. Meronts of both generations were bounded by a double pellicular membrane and were situated free in the host cell cytoplasm. Merozoites formed by endopolygeny that involved multiple intranuclear spindles of a single, large irregular nucleus. First-generation meronts measured 22.6 .times. 17.1 .mu.m (19-28.7 .times. 7.5-24 .mu.m) and contained 120-240 merozoites, which measured 7.1 .times. 1.6 .mu.m (4.8-7.5 .times. 1.3-1.8 .mu.m). Corresponding values for 2nd-generation meronts were 13.2 .times. 9.2 .mu.m (8.3-15 .times. 7-13.5 .mu.m), 32-80 and 5.8 .times. 1.7 .mu.m (5.6-6.2 .times. 1.4-2.2 .mu.m).