Ultrastructural and Cytologic Studies of the Sporozoites of Four Eimeria Species *

SYNOPSIS. Studies were made with the light microscope of live sporozoites of E. ninakohlyakimovae and E. ellipsoidalis as well as sporozoites fixed with Schaudinn's, Stieve's and Zenker's fluids, methanol and ethanol saturated with picric acid. Sporozoites were stained with Giemsa, bromphenol blue, modified PAS‐AO, Feulgen, Harris’hematoxylin and eosin Y, and iron hematoxylin. Sporozoites of the above species as well as those of E. auburnensis and E. bovis were also fixed with glutaraldehyde and osmium tetroxide or negatively stained for study with the electron microscope. Living sporozoites had gliding, pivoting, flexing, and probing movements. Each sporozoite of each species was covered by a pellicle consisting of an outer limiting unit membrane that was continuous around the sporozoite and an inner membrane that terminated at the polar ring. Twenty‐four subpellicular microtubules were longitudinally arranged just beneath the inner membrane. At the anterior end of the sporozoites was a protruded or retracted conoid composed of spirally‐arranged fibrillar structures, 2 rings anterior to the conoid, and the polar ring, a thickening at the anterior termination of the microtubules and inner membrane. Other organelles observed with the electron microscope were a nucleus with or without a net‐like nucleolus, club‐shaped organelles, refractile bodies, micronemes, endoplasmic reticulum, Golgi apparatus, mitochondria with tubular cristae, micropores, lipoid‐like bodies, oval polysaccharide bodies and ribosomes. The fine structure of these sporozoites is compared to that of related Sporozoa.