The fine structure of the endogenous stages of Eimeria labbeana. 4. Microgametogenesis.

The fine structure of the microgamonts and microgametes of Eimeria labbeana from the columnar epithelial cells of the ileal mucosa of experimentally infected pigeons, Columba livia, has been described and compared with that of similar stages in other species of Eimeria. The microgamonts averaged 8.0 X 10.0 mum (6.7-8.4 X 9.0-11.4 mum), had a maximum number of 27 nuclei each (0.8-1.0 X 1.0-1.3 mum), and showed various stages of mitotic nuclear divisions without the appearance of detectable mitotic spindles. Modification of the membrane of some of the nuclei into spirally coiled structures containing granular bodies resembling autophagosomes were observed. One pair, and occasionally two pairs of centrioles with the typical (9 + 1) microtubular composition were seen in association with some of the nuclei. Polysaccharide granules were seen in only about 5% of the more than 2,000 microgamonts studied. Cytomere formation was not observed but development of microgametes in association with intra-cytoplasmic spaces, and surface invaginations was frequently seen. Microgametes were elongate to slightly curved, averaged 3.1 X 1.2 mum (2.8-3.3 X 0.8-1.3 mum), and each was composed of an apical perforatorium, 2 basal bodies, 2 flagella, 4 microtubules located representing a third but rudimentary flagellum, a row of more than 15 short microtubules located laterally in the apical region, a large nucleus (1.7 X 0.8 mum), and a mitochondrion. Subfibrillar composition of the basal body and basal-plate region was observed. The microgametes of E. labbeana are the shortest and stoutest ever reported from the genus Eimeria. The maximum number of microgametes detected from any one section was thirty.