1. The livers of fifteen out of sixteen monkeys exhibiting P. kochi in the peripheral blood showed white or translucent spots which are thought to represent a stage in the development of the parasite. The livers of seven monkeys consistently blood negative were spotless.
2. Smears of these spots or merocysts contained numerous free merozoites and unpigmented schizonts of varying size. A characteristic feature of the schizont is the presence of one or more vacuoles.
3. Sections reveal the development of cytomeres which later coalesce to form a cyst wall packed with merozoites.
4. The host reaction is characteristic—at first, there is a great concentration of polymorphs, and later these are replaced by fibroblasts and giant cells.
I have great pleasure in thanking Dr. C. M. Wenyon and Dr. Cecil Hoare for examining part of the material and for making' various suggestions.