_Synonymy._--_Nosema periplanetae_, _Pleistophora periplanetae_ [after Semans, 1943]. Georgévitch (1953) has pointed out that one may find in the malpighian tubules of cockroaches a mixed infection of Microsporidia, Haplosporidia, and Mycetozoa, and that some of the discrepancies in the earlier literature may be attributed to attempts to combine in one organism disparate stages belonging to different orders. See also comments under _Coelosporidium periplanetae_, _Haplosporidium periplanetae_, and _Peltomyces periplanetae_. _Natural hosts._--_Blatta orientalis_, France (Mercier, 1906a; Debaisieux, 1927); England (Perrin, 1906, 1906b); U.S.S.R. (Zhivago, 1909); Yugoslavia (Georgévitch, 1925, 1926, 1926a, 1927); Germany (Wellmer, 1910, 1911). _Blattella germanica_, France (Léger, 1909; Debaisieux, 1927); U.S.S.R. (Zhivago, 1909). _Periplaneta americana_, Brazil (Lutz and Splendore, 1903). This organism lives in the lumen of the malpighian tubules of cockroaches. The cited authors appear to have been convinced that this organism was a microsporidian. Georgévitch (1927, 1953) described the polar capsule and filament characteristic of this order. =Plistophora= sp. _Natural host._--_Blatta orientalis_, France (Mercier, 1908a): The organism parasitized the fat body of the cockroach. Mitoses, often abnormal, were induced in the fat cells. Infected cockroaches were easily recognizable by their distended abdomens. The fat body became chalky white and showed through the intersegmental membranes. Porter (1930) reported finding an unidentified microsporidian in the fat bodies of _Blattella germanica_ and _Periplaneta americana_ collected in South Africa. It may or may not have been a species of _Plistophora_. Class CILIATA Order HOLOTRICHA Family PARAMECIIDAE =Paramecium= sp. _Natural associate._--Cockroaches, U.S.A., Maryland (Cleveland, 1927): Three of 30 cockroaches collected in the basement of a department store had paramecia in their stomachs but none in the rectum. _Experimental associate._--_Periplaneta americana_, U.S.A. (Hegner, 1929): Paramecia fed to the cockroaches were recovered from the crop at intervals from one-half to six and one-half hours. In no case were the protozoa recovered from the stomach alive. Cockroaches, U.S.A., Maryland (Cleveland, 1927). About 200 starved cockroaches were fed a culture of _Paramecium_. Few, if any, of the protozoa were killed in the stomach during the first two hours, but all were killed within 5 to 6 hours after ingestion. Family ISOTRICHIDAE =Isotricha caulleryi= Weill _Natural host._--_Periplaneta americana_, Indochina (Weill, 1929): Alimentary canal. Order SPIROTRICHA Family BURSARIIDAE =Balantidium blattarum= Ghosh _Natural host._--_Periplaneta americana_, India (Ghosh, 1922; Bhatia and Gulati, 1927); Gold Coast Colony (Macfie, 1922): Intestinal tract. * =Balantidium coli= (Malmsten) _Experimental vector._--Cockroach, Venezuela (Tejera, 1926). =Balantidium ovatum= Ghosh