PLATES 58 TO 62(Received for publication, January 16, 1959) ABSTRACT Comparative electron microscope investigations on sections of the lens cortex of the normal, mature rat, rabbit, monkey, and the normal calf reveal similar patterns of intracellular organization.The superficial lens fiber contains a nucleus, mitochondria, endoplasmic reticulum, dense granules, Golgi complex, and a quantity of small structures of low opacity which appear as filamentous and spherical configurations.Variations in number, distribution, and spatial arrangement of cytoplasmic elements in lens fibers are described. These changes in the pattern of cytoplasmic organization are concomitant with development of fibers and their displacement towards the center of the lens. Structural details of the various zones of the lens epithelium and the lens fibers are compared.

SYNOPSIS. The reproduction of Toxoplasma gondii has been investigated in osmium fixed and sedimented mouse peritoneal exudate. The material was obtained 9 days after intraperitoneal inoculation with the Beverley strain. Predominantly intracellular organisms were seen in various phases of multiplication and indicated the occurrence of three different modes of reproduction. One is a schizogonic cycle, whereby at least four progenies are delineated within a rosette‐shaped, multinucleated Toxoplasma cell. They subsequently separate to become individual parasites. The second mode is considered as a special type of schizogony that results in the production of only two merozoites within one parent cell. This process previously has been designated as endodyogeny. Finally, the observations suggest division by binary fission as a third type of reproduction. From these results, it is possible to relate the genus Toxoplasma, previously regarded as a protozoon of uncertain classification, to the class Sporozoa.

SYNOPSIS. Toxoplasma aggregates in sub‐acutely and chronically infected mouse brain were studied with special regard to interparasitic relationships, encapsulating wall formation and host‐parasite interaction. The individual parasites within a cyst are separated from one another by an opaque substance which also appears as a component of the cyst wall. A second constituent in the wall consists of vesicular and membranous structures which presumably are derived from the endoplasmic reticulum of the host cell. In small cysts, the organising are loosely arranged and maintain the typical crescentic shape whereas, in large cysts, they are tightly packed and polygonal in outline. It is concluded from the data obtained that only the term “cyst” correctly designates these parasitic aggregates.