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.

A biological study of the fauna of sewage-treatment plants was pursued by the writer for two years, from June 1927, thanks to the generosity of the Grocers' Company. The programme laid down included a qualitative and quantitative survey of the fauna and a collection of data on such physico-chemical factors as hydrogen ion concentration and oxygen requirement, with a view to seeking correlations between the two groups of phenomena.

This is the third and final paper of a series which constitutes a report on a biological investigation of sewage, undertaken by the writer as a Research Scholar of the Grocers' Company. Of the previous two papers, the first (1929) describes a colorimeter and the second (1930) is a general report on the work as a whole. Since the nematodes form a neglected and not inconsiderable section of the fauna of most sewage plants, special attention was accorded them, and an account of them is given separately here instead of rendering the general report unbalanced and unwieldy by being included there.