Early in 1938 the writer received a tube of nematodes from Mr. Colin Smee, Entomologist, Department of Agriculture, Zomba, Nyasaland, collected from a rotting peach fruit in which he had been trying to hatch fruit-flies. According to Mr. Smee's letter the worms had formed masses in the fruit and had also appeared on the surface as waving threads or tendrils composed of numerous eelworms massed together. The material had been fixed in glycerine alcohol and consisted of numerous adult males and females as well as large numbers of larval forms. Fixation was not good as although the gross morphology and anatomy was fairly easily discernible, some of the finer structural details were not as clear as one could have wished.

In water extracts of turf from one of the meadows at this Institute made May and November, 1941, several specimens of a new dorylaimid nematode were obtained. They were noticeable even under low magnification by reason of the elongated mouth spear and the shape of the tail. Females only have been found. Study of freshly-killed and well preserved specimens showed that they belong to the genus Pungentus of Thorne & Swanger (1936). As, however, they do not agree structurally with any of the species described by Thorne & Swanger (l.c.) and by Thorne (1939), a new species is erected for their reception. The worms are named in honour of Dr. Gerald Thorne, who in the two monographs just cited has added so materially to our knowledge of the soil nematodes belonging to the superfamily Dorylaimoidea.

Studies carried out by the writer during the past few years on various species of the genus Anguillulina, associated chiefly with the roots of grasses, have resulted in the-collection of numerous other species of soil nematodes including many representatives of the predatory genus Mononchus. Amongst these are specimens of Mononchus tridentatus de Man, 1876, M. brachyuris Bütschli, 1873, two species in which males as well as females are known, M. muscorum (Duj. 1945), M. punctatus Cobb, 1917, M. papillatus Bast., 1865 and M. minor Cobb, 1893; all species in which females only are known. Investigation of these forms has resulted not only in the discovery of facts concerning their feeding habits but also of certain interesting anatomical features which have hitherto remained incompletely elucidated in members of this genus.

Two new species of Multiceps are described. M. macracantha n. sp. a parasite of the white rat in Rhodesia, is distinguished by the possession of very large hooks. M. otomys n. sp. from a mouse, Otomys erroratus in Pretoria; has fairly large hooks of a characteristic appearance and shape.

The fact that the large taeniid hook appears to develop from at least two centres of chitinization is noted.

The genus Multiceps has come under intense observation recently and the validity of the various species has been considered. The hook, being of a chitinous nature and therefore presumably of a less variable disposition than most other points, has been used for specific diagnosis, though as has been shown earlier, even this structure is not entirely satisfactory. But there is no other structure that is more satisfactory. When the information has been available, the blade length has been used as this is the most constant part of the hook. The small hook is of little or no diagnostic value. In many cases, however, only the range of the total length has been known.

1. “In vitro” experiments show that sulphur dioxide is very lethal to cysts of the potato eelworm. Its effect is very much more potent under moist conditions than under dry. The other factors, concentration and time are secondary in their action as compared with humidity.

2. Fumigation of seed potatoes for 24 hours under conditions appropriate to bacterial fumigation results in the complete destruction of the cysts adherent to them.

3. The sulphur dioxide fumigation is without any significant effect on the tubers provided it is carried out previous to chitting. It has little if any effect on the chitting power of the potato but is lethal to any chits already formed.

(1) A technique for measuring the infectivity of soil with Heterodera schachtii in terms of the number of larvae potentially capable of infecting plants per pound of soil is described.

(2) The liberation of the larvae is accomplished by subjecting the cysts recovered from one half-pound sample of soil to a given strength of calcium hypochlorite solution for four hours. The loss of larvae due to solution during this time was found to be negligible.

(3) It was shown that if the larvae liberated were made up to a suspension, then counts made on 0·15 cc. samples of this suspension fall into a Poisson distribution and hence the accuracy of the final determination is dependent only on the number of larvae counted.

(4) It was found that provided the soil to be examined was thoroughly mixed that it was unnecessary to examine more than one half-pound sample as there was no significant difference between the means from different samples.

(5) Figures of cyst counts tabulated alongside available larvae show the utter inadequacy of cyst counts as a measure of infectivity.

(6) No attempt is made in this paper to determine how many of the larvae are alive and viable, further research into this matter being contemplated.