The Fine Structure of Microgametocytes of Eimeria perforans, E. stiedae, E. bovis, and E. auburnensis

The microgametocytes of Eimeria perforans, E. stiedae, E. bovis, and E. auburnensis were comparatively studied with the electron microscope. Of these only E. stiedae and E. bovis are known to be pathogenic. In each of the species, except for E. auburnensis, the nuclei assumed a peripheral position after completion of nuclear multiplication. At this stage the nucleolar material was arranged in a layer at the periphery of the nucleus in all four species; few or no pores were seen in the nuclear membrane. Numerous mitochondria were present in the vicinity of the nuclei. Usually, glycogen granules and thick-walled inclusions, possibly representing lysosomes, were also present in the cytoplasm, and the endoplasmic reticulum was well developed. In the giant microgametocytes of E. auburnensis, the nuclei did not become peripherally located. Instead, the protoplasm was sub-divided into numerous small masses by the development of a network of spaces connected with the vacuole surrounding the parasite. This greatly increased the cell surface, and facilitated the formation of the large number of microgametes characteristic of this species. In E. stiedae, a large mitochondrion was frequently found in the perinuclear space; this mitochondrion is likely the one that becomes incorporated into the microgamete. Micropores were present at the surface of E. bovis microgametocytes. In this species, the spatial relationship between host cell and parasite was closer than in the other species. Along the boundary between the microgametocyte and the host cell, outward processes of the parasite alternated with inward processes of the host cell. In each of the latter processes a mitochondrion, frequently showing degeneration of cristae, was located. Conclusions as to relationships between fine structure and pathogenicity must await further work.