Certain species of the nematode genus Anguillulina which commonly occur in close association with the roots of grasses are known to invade the root cortex and to reproduce therein. Thus Anguillulina pratensis, A. obtusa and A. erythrinae all occur in the roots of Agrostis stolonifera L. in pastures at this Institute. The writer has on a few occasions, also found one or two specimens of the small tapering-tailed species, A. agricola and A. costata, within the root cortex of the same kind of grass but further observations are needed before we can say definitely whether these two species actually parasitize roots and reproduce within the tissues. An occasional specimen of A. intermedia has also been found by the writer once or twice inside root tissues but never in what could be regarded as fresh, sound roots, and in view of Linford's (1937) observations on the ability of this species to feed upon fungal hyphae, it is probably safest to regard it as not a true parasite. The examples found may have entered partly decayed roots in search of fungal hyphae.