1. Of 259 cockroaches (Periplaneta americana) collected at Manhattan, Kansas, 86·3 per cent. were infested with one or two species of oxyurids, Leidynema appendiculata and Hammerschmidtiella diesingi. The highest incidence was among the immature roaches, of which 94·2 per cent. were infested; next was in the adult females with 87·5 per cent. infested; and lastly among the mature males with 79·5 per cent. parasitised. The female roaches carried the heaviest infestations and the young Periplaneta americana the lightest.2. Uninfested cockroaches were obtained by rearing the young from oöthecae.3. Oxyurid eggs in moist chambers remained viable for at least two months. Eggs of all stages when exposed to direct strong artificial or natural light for 15 min. failed to continue development.4. Fertilised eggs incubated at 37° C. in dilute Locke's solution develop to the active embryonated stage in 20–36 hours; in 4–7 days they develop to the resting embryonated stage.5. Regardless of the media utilised eggs failed to hatch in vitro.6. Feeding experiments proved that transmission is direct. Eggs in the resting embryonated stage are infective; those in the active embryonated stage do not appear to be infective.

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