The worms are found in the colon and rectum of the host. Galeb (1878) found as many as 20 individuals in a single _B. orientalis_. Sobolev (1937) found 52 percent of _B. orientalis_ infected with _L. appendiculata_; the mean number of worms per roach was 1.5 and the maximum 2. Dobrovolny and Ackert (1934) found 69 percent of 222 _P. americana_ infected with this species. Two molts occur within the egg during development of the larva. The first molt occurs outside the host resulting in the formation of an infective resting stage. The second molt occurs inside the cockroach (Todd, 1941, 1944). Transmission of the nematode is direct, eggs in the resting embryonated stage being infective (Dobrovolny and Ackert, 1934). Hoffman (1953) described a filamentous bacterium, _Streptomyces leidynematis_ Hoffman, which grows on the cuticle of _L. appendiculata_ in _P. americana_. Leidy (1853) noted the presence of simple, inarticulate, amorphous filaments, growing from nematodes infecting _B. orientalis_. Bütschli (1871) and Magalhães (1900) described similar filaments adhering to the surface of oxyurids from cockroaches. =Leidynema appendiculata= (Leidy, 1850) Chitwood, 1932? _Natural host._--_Eurycotis floridana_, U.S.A., Massachusetts (Roth and Willis, unpublished data, 1955): Determined by Dr. G. Steiner who wrote us, "In _Eurycotis floridana_ there were ten specimens of the nematode _Leidynema appendiculata_ (Leidy, 1850). This cockroach is obviously a new host for this nematode. I am not sure that the nematode exactly agrees with the description as given in the literature." =Leidynema cranifera= Chitwood, 1932 _Natural hosts._--_Blaberus craniifer_, U.S.A., Florida (Chitwood, 1932); Massachusetts (Roth and Willis, unpublished data, 1955). Determined by Dr. G. Steiner. _Blaberus atropos_?, U.S.A., Florida (Chitwood, 1932): _B. craniifer_ has generally been recorded as _B. atropos_ of Stoll which is a closely related but distinct South American species (Rehn and Hebard, 1927). =Leidynema delatorrei= Chitwood, 1932 _Natural host._--_Leucophaea maderae_, Cuba, Havana (Chitwood, 1932). =Leidynema nocalum= Chitwood and Chitwood, 1934 _Natural host._--_Panesthia angustipennis_, Philippine Islands (Chitwood and Chitwood, 1934). =Leidynemella fusiformis= Cobb, 1934 _Natural hosts._--_Panesthia laevicollis_?, Philippine Islands (Cobb _in_ Chitwood and Chitwood, 1934). _Panesthia angustipennis_, Philippine Islands (Chitwood and Chitwood, 1934). =Leidynemella panesthiae= (Galeb, 1878) Chitwood and Chitwood, 1934 _Synonymy._--_Oxyuris panesthiae_ Galeb, 1878, in part; _Thelastoma panesthiae_ (Galeb, 1878) Travassos, 1929. [Chitwood, 1932; Chitwood and Chitwood, 1934.] _Natural host._--_Panesthia_ sp., New Guinea (Galeb, 1878): About 40 nematodes may be found in one insect. =Leidynemella paracranifera= Chitwood and Chitwood, 1934 _Natural host._--_Panesthia angustipennis_, Philippine Islands (Chitwood and Chitwood, 1934).