A Study of Excystation in Nyctotherus ovalis: With Notes on Other Intestinal Protozoa of the Cockroach

The main purpose of the present paper is to give an account of the development of the ciliate Nyctotherus ovalis from its resting phase, and of its final emergence from the cyst wall as a free-swimming trophozoite. The process was initiated experimentally by feeding the host with cysts and was then watched throughout under the microscope in a fresh preparation of the midgut contents. Attempts were also made to test the efficacy of certain environmental factors in stimulating the organism to excyst. Of those so far tried, a rise of temperature to 28 to 30? C. has proved successful. The remaining subject matter deals mainly with a few observations on the other Protozoa of the cockroach, made during experiments on Endamoeba blattae. The work on the latter form was carried out with