A new species, Otodistomum plunketi, is described from the Lord Plunket's Shark Scymnodon plunketi caught in Otago Harbour, New Zealand. This species is compared with Otodistomum veliporum and O. pristiophori, from which it is mainly distinguished by its size, shape, egg-size and undulating caeca.

An attempt to differentiate by means of the electron microscope between particles of the top and bottom components of the turnip yellow mosaic virus is described. Since the particles of the top component are thought to be hollow spheres, it might be expected that they would collapse after drying and thus throw a smaller shadow than the particles of the bottom component which are thought to have a more solid centre. No difference could be perceived between the two types of particle, so that the apparently hollow particles can withstand the effect of drying without collapsing.

Sections were cut of leaves of Chinese cabbage (Brassica chinensis) and particles were observed inside the cells which could conceivably be virus particles.

The present paper is the third of a series dealing with a collection of parasitic worms from fishes off the coast of Iceland. The two previous papers have been concerned with the Cestoda and Digenea respectively (Rees, 1953a, b). There are no existing records of Monogenea, Nematoda or Acanthocephala from fishes off the coast of Iceland. Although this collection is not a large one, it indicates a wider geographical range of parasites already recorded from marine fishes in other parts of the world. There are five new host records.

We believe that the publication of a new key to the species of the genus Polyplax, so soon after that contained in Ferris's recent monograph (Ferris, 1951), is justified since it includes two new species and three species, praomydis Bedford, subtaterae Bedford and cummingsi Ferris, which appear to require some re-definition as Ferris placed all three in synonymy.

Among a large collection of alcohol material of Danish fleas, belonging to the Universitetets Zoologiske Museum at Copenhagen and kindly sent to me for identification by Dr S. L. Tuxen, was a tube which not only contained the fleas Chaetopsylla trichosa Kohaut (6 ♂, 22 ♀) and Paraceras melis melis (Walker) (3 ♂, 30 ♀), but also a large number of the chewing louse Trichodectes melis (Fabricius). These female of Trichodectes melis, is firmly attached on the outside of the left mid-tibia by having its mandibles entirely surrounding the tibia (Fig. 1). The two insects have been mounted on one slide (which is incorporated in the British Museum collection of fleas at Tring) and the attachment of the louse to the flea is so firm that the act of preparation did not separate the two insects.

In August 1952 one of the authors captured a series of rodents of the type Rattus rattus alexandrinus at Costermansville. The rats were examined at the Medical Laboratory, Astrida (Ruanda), by kind permission of the Director, Doctor J. B. Jadin. Two species of trombiculids were found in one ear, which was very scabby and contained other microscopic arachnidians.

From the Virus Research Institute, Entebbe, Uganda, the author received a number of tubes containing mites collected from small mammals in the course of yellow fever investigations. One of the tubes with mites taken from a hyrax (Procavia ahyssinica meneliki Neumann) contained two new species of larval Trombiculidae which are described in this paper under the names Schöngastia haddowi sp.n. and Eutrombicula lumsdeni n.sp. in honour of the donors, Drs A. J. Haddow and Russell M. Lumsden.

Dipetalonema sprenti n.sp. is described from specimens removed from the peritoneal cavity of beavers (Castor canadensis) from Ontario, Canada. D. sprenti is found to be similar to D. arbuta Highby, 1943, but differs in the larger size of the eggs and fully developed embryos, the greater lengths of the spicules, the arrangement of the medial post-anal papillae, the more posterior position of the nerve ring, the greater length of the tail and in the considerably larger size of the body. D. sprenti is the fourth species of Dipetalonema described from rodents.

1. The description of the female and nymph of the so-called variety I. percavatus var. rothschildi is enlarged.

2. As far as the evidence is available it parasitizes marine birds and is probably a three-host tick.

3. Its systematic affinities are discussed, and since I. percavatus is synonymous with I. auritulus, then the variety of Nuttall & Warburton should be raised to the specific rank of I. rothschildi.

On the available data from south Wales and southeast England, the tick Ixodes hexagonus Leach has spring and autumn peaks of activity on hedgehogs, stoats and weasels.

One or more stages of this tick have been recorded on fifteen mammalian hosts. All stages have been collected from hedgehogs, stoats, foxes, polecats and ferrets. The weasel is probably the smallest habitual host. No specimens of I. hexagonus have been found on birds.

Man is an ‘accidental’ host and records of this tick on man in the London area are given. From the present information it seems that ill-effects following the bite of this parasite are rare. In built-up areas the probable sources of infestation are dogs, cats and hedgehogs. Air-raid shelters and similar constructions which have harboured these hosts at one time or another may provide a centre of infestation of man. Our observations indicate that the number of ticks in most hedgehogs' nests is not large. Nothing is known of the tick population in the habitats of other hosts. It is suggested tentatively that the ticks may drop off hedgehogs away from the nest and that after further development (i.e. hatching of eggs and metamorphoses of later stages) they are picked up by such animals as foxes, stoats, weasels.

The records of this tick in Britain are summarized and they indicate that I. hexagonus is a southern species.

1. A new species of tick, I. theileri from South Africa, is described. Hitherto it has been collected only from birds.

2. Existing descriptions of I. daveyi Nuttall 1913 and I. brunneus Koch 1844 are amplified, and the synonymy of I. frontalis (Panzer, 1795) discussed.

3. Diagnostic characters, whereby I. daveyi, I. brunneus, I. frontalis and I. theileri may be separated, are tabulated.

1. Strains of P. berghei resistant to sulphadiazine, pyrimethamine, and methylene blue were produced by treating acute infections with low doses of drug.

2. The strain resistant to methylene blue was sensitive to pamaquin, mepacrine, sulphadiazine, proguanil, pyrimethamine, and 2 : 4-diamino-6 : 7-camphano-pteridine.

3. The pyrimethamine-resistant strain was cross-resistant to proguanil and its active metabolite CPT, 2 : 4-diamino-6 : 7-camphanopteridine, 2 : 4-diamino-6 : 7-(l′-ethylindolo)-pteridine, and 2 : 4-diamino-5-p-chlorophenylpyrimidine.

4. The sulphadiazine-resistant strain was cross-resistant to pyrimethamine, sulphanilamide, proguanil and its active metabolite CPT, 2 : 4-diamino-6 : 7-dinhexylpteridine, and 2 : 4-diamino-6 : 7-diisopropylpteridine. It was as sensitive as the parent strain to quinine, mepacrine, chloroquin, pamaquin, methylene blue, and M 3349.

5. The action of sulphadiazine against the sulphadiazine-resistant strain was inhibited by the same doses of p-aminobenzoic acid and folic acid as were required with the parent strain, although the dose of sulphadiazine was increased 30-fold.

1. Entamoeba moshkovskii was isolated from a sewage plant in North London.

2. The morphology and metacystic development is similar to that of E. histolytica and other histolytica-like amoebae, but with differences in minor details.

3. The cysts of E. moshkovskii remain viable when kept at 4° C. for periods up to 10 months providing they are not allowed to dry.

4. If the amoebae are placed in hypotonic solution, the amoebae attempt to eliminate excess water by means of contracting vacuoles, but they eventually die.

5. Experiments have shown that E. moshkovskii is an anaerobe.

6. The optimum temperature for growth is about 24° C. as encystation does not occur at 37° C.

7. E. moshkovskii is not infective to rats or to larvae of the common frog (Rana temporaria) and Salamandra maculosa.

Types. Four mature females (NM. 5728) from Myotis tricolor, Town Bush Cave, Pietermaritzburg, March 1952.

1. The width and length of eggs of Haemonchus contortus, Cooperia curticei, Trichostrongylus axei, T. vitrinus, Bunostomum trigonocephalum, Chabertia ovina, Oesophagostomum venulosum and Ostertagia spp. were measured.

2. Frequency distributions of the linear dimensions of the eggs of each species are given, together with the frequencies calculated on the assumption that the distributions are normal.

3. A method of species differentiation based on egg measurements is described, the method being based upon the statistical chances of eggs of different species falling into particular size classes.

4. The application of the method and the construction of a classifying scale are described.

On 7 March 1953 I received several specimens of Locusta migratoria from Mr T. Singh, who found them dying in the breeding cages at the Imperial College, London. Microscopic examination showed that the fat body contained large numbers of oval-shaped spores belonging to a microsporidian.

The nematodes described here were collected by biologists of the Australian National Antarctic Research Expedition based at the subantarctic stations at Macquarie Island and Heard Island, over the years 1948–51.