The material forming the basis of this paper consists of the two fungi, Catenaria anguillulæ Sorokin and Rhizophidium carpophilum Zopf, which were found parasitic on the eggs of Dibothriocephalus latus in the Helminthology Department in March, 1927. The stool containing the eggs had been washed in laboratory tap water and this was evidently the vehicle of the fungus infection. A sediment obtained from one of the water tanks from which the laboratory is supplied was found to contain infusoria, rotifers and other forms likely to act as hosts for the fungi, and that this was the source of the original infection was proved on more than one occasion by placing some of the sediment in a petri dish along with some uninfected eggs of D. latus, when a new infection of both the fungi appeared in the eggs.

In the following paper the fungi are described and an account is given of some experimental work that was carried out with a view to determining the possibility of employing such parasites as a control measure in helminthiasis.

As Looss has shown, the larvæ of Ancylostoma can infect a suitable host by penetrating the healthy skin. If we place the infective material on the surface of the skin, after a short time we find the larvæ in the subcutaneous tissue. The same behaviour is shown by the filariform larvæ of Strongyloides siercoralis, which provide more convenient material for examination, because they can be collected very easily in pure culture and free from fluid by the special culture-method described by me (1924), the principle of which depends on the well-known fact that the filariform larvæ of Strongyloides and other nematode larvæ, accumulate in the form of white filaments of several millimetres in length (fig. 3), each consisting of thousands of individual larvæ, on little prominences in their vicinity, all being guided to similar places by the same sets of “tropisms” (Fülleborn, 1924).

In the course of work undertaken in the preparation of the experimental field plots at Winches Farm it has been of interest to ascertain something about the nematode fauna of the place, especially that occurring in certain heaps of manure made at the farm and afterwards used on some of the plots. With regard to the worms recorded from sheep droppings collected from pastures these were obtained in Baermann extractions, set up by a colleague, in attempts to collect larvae of parasitic nematodes harboured by the stock. It became necessary for purposes of differentiation to determine the naturally occurring free-living nematodes which were found in great abundance. The worms described in the following pages have been encountered in the course of these investigations. Some are new to science and about others very little has previously been known so that additional information on them is here made available.