In a paper recently published in the Philosophical Transactions of the Royal Society of London, the writer describes the discovery of certain small Tylenchoid nematodes in the swollen stems of the seedling oats suffering from frit-fly attack at Winches Farm, St. Albans. Adults of both sexes and larvæ undergoing the last two moults were found in the destroyed plant tissues surrounding the fly larvæ. The spermatized female worms were next discovered within the body-cavity of the frit-fly larvæ. In due course, they were obtained from pupæ of the fly, having increased in size, and finally were found within adult flies of both sexes lying coiled within the abdomen as comparatively large sausage-shaped worms. As a result of the presence of the worm, the flies are sterilised, being unable to develop their reproductive organs. The worms become viviparous and shed large numbers of larvæ into the body-cavity of the fly and these, after undergoing a certain amount of growth, make their way into the gut of the host and pass to the exterior via the anus. In the present communication a brief account is given of the principal observations on the new parasite, its life-history and the effects on the host, described in detail in the original paper.