Fine structure of the endogenous stages of Eimeria labbeana. I. The first generation merozoites.

The fine structure of the 1st generation merozoites of Eimeria labbeana from the ileal mucosa of artificially infected pigeons (Columba livia) was investigated and described. The 1st generation merozoites which appeared between 36-48 hr after infection averaged 4.4 times 2.1 mum in size. The 3-membraned pellicle was irregular in texture and harbored a single micropore, and many micropore-like invaginations. Closely apposed to the inner pellicular membrane were seen 22 microtubules, each 22-25 nm in diameter. An apical vesicle, 50 nm in diameter, seen at the anterior extremity, was connected with the common duct of the micronemes. The conoid consisted of 9 spiral elements, each 30 times 25 nm. The paired organelle (rhoptries) varied in length (1.4-2.2 mum), and the ductules (23 nm diameter) were composed of 2 inner tubules, each 6 nm in diameter. A unit membrane enveloped the partially alveolar and differentially osmiophilic interior of the bulbous regions of the rhoptries. The "rod-like structure" was found to be tubular and represented the common duct of the micronemes.