The Development of Megaloschizonts of Leucocytozoon simondi Mathis and Leger.*

SUMMARY. Susceptible ducklings were exposed to natural infection during a limited time, and infections of supposedly known duration were obtained. Slides of tissues from these ducklings were prepared by common histological techniques. Comparative materials were provided by cooperators. On the basis of study of these tissues what seems a logical description of development of megaloschizonts of Leucocytozoon simondi was formulated. The earliest stage found was the trophozoite. There is no evidence of schizogony in this form; the only internal structure is the nucleus. Prior to any schizogony there is a marked increase in the amount of chromatin in the nucleus, especially on the periphery. It is hypothesized that as the chromatin increases, buds are evaginated from the margin of what may then be called the central body and are set off to form spherical primary cytomeres. The chromatin of primary cytomeres first diffuses and then proliferates to form peripheral clusters. These clusters of chromatin separate to form secondary cytomeres which continue to multiply in the same manner. The production of cytomeres by the central body and by division of primary and secondary cytomeres eventually fills the cytoplasmic area of the megaloschizont. Apparently pressure within the schizont then shapes the course of further development. The central body ceases to function as a primordium and becomes compressed. The multiplying cytomeres become smaller and more granular in appearance, and their chromatin becomes more concentrated. Merozoite‐like bodies are eventually produced. These reproduce until the central body is greatly compressed and the membrane enclosing the megaloschizont is ruptured and releases the merozoites.