Electron Microscope Observations on the Development of First-Generation Merozoites of Eimeria bovis

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Abstract
At the earliest stage observed in the development of the first-generation merozoites of Eimeria bovis the schizont cytoplasm was subdivided into many lobes or spheroidal blastophores; their peripheries being lined by the many nuclei resulting from repeated divisions. The beginning of merozoite production is characterized by the formation of a complex of structures which later comprises the anterior end of the merozoite. A thickened layer forms under the plasma membrane and eventually becomes the inner membrane of the merozoite. Adjacent to a central opening in this layer lies a conoid. Subpellicular fibrils, which radiate from the opening, are closely applied to the inner membrane. As development proceeds, the blastophore membrane is elevated into a cone-shaped projection which later elongates into a fingerlike bud. This bud, the developing merozoite, contains the primordia of the paired organelle, a nucleus with adjacent Golgi apparatus, and other cytoplasmic constituents derived from the blastophore. With further growth of the merozoite, the outer and inner membranes become extended posteriorly; after the early stages, this is associated with an infolding of the membranes into the blastophore. In a late stage of development, the merozoites are completely formed except for an attachment of their posterior ends to the remains of the blastophore. Finally, the attachment is broken, resulting in free merozoites and residual bodies.