Observations on the Life Cycle of Eimeria bilamellata Henry, 1932 in the Uinta Ground Squirrel Spermophilus armatus*

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Abstract
SYNOPSIS. Oocysts of Eimeria bilamellata were found in Spermophilus armatus, Utah and Wyoming; S. beecheyi, California; and S variegatus, Utah. Oocysts were not found in S. lateralis, S. richardsoni, S. columbianus, S. tridecemlineatus, or the white‐tailed prairie dog, Cynomys leucurus. Experimental infections were established in S. armatus, S. variegatus, and S. lateralis, but not in S. richardsoni, least chipmunks Eutamius minimus, laboratory rats Rattus norvegicus, or Mongolian gerbils Meriones unguiculatus. After one experimental infection S. armatus and S. variegatus were immune to further infections. Spermophilus lateralis could be infected 3 or 4 times before the animals were immune. However, individuals of S. armatus in a natural population had more than one infection with E. bilamellata; probably infections must be of a certain level before immunity develops. When S. armatus were inoculated with about 100,000 oocysts, the animals usually died on the 7th day after incoculation.Oocysts were 33‐37 by 25‐31 μ (mean 34.5 by 28.2 μ). The oocyst wall was brown and composed of 2 layers. A distinct micropyle was present. Sporocysts were 18‐23 by 9‐12 μ (mean 19.9 by 10.3 μ). In experimental infections, the prepatent period was 10 days and the patent period 5–21 (mean 9) days. Schizonts were 1st seen 7 days after inoculation. They were located above the host cell nuclei of epithelial cells at the tips of the villi of the jejunum and ileum. One or more earlier generations of schizonts were thought to occur, but these were not observed. Gametogony took place in epithelial cells of the jejunum and ileum. Shortly after the merozoites entered the cells, the cells became enlarged and were displaced into the lamina propria. The microgametocytes were considerably larger than the macrogametes and contained a central residual body. Macrogametes had a peripheral eosinophilic layer as well as cytoplasmic granules; both apparently participated in formation of the oocyst wall.
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