1. 2:4-diamino-6:7-diisopropylpteridine has an antimalarial index of 1:40, when tested against Plasmodium gallinaceum.

2. 2:4-diamino-1′-methylindolo-(2′:3′-6:7)-pteridine showed no activity against P. gallinaceum in doses tolerated by the chick.

3. Proguanil- and sulphadiazine-proguanil-resistant strains of P. gallinaceum were cross-resistant to 2:4-diamino-6:7-diphenylpteridine.

4. Proguanil- and sulphadiazine-proguanil-resistant strains of P. gallinaceum showed no cross-resistance to 2:4-diamino-6:7-diisopropylpteridine, but were slightly hypersensitive to this compound.

I wish to thank Dr A. Bishop for her interest in this work, and for advice and criticism. The work has been financed by the Medical Research Council.

1. Permanent and temporary pastures were examined using a modification of Taylor's method.

2. The goodness of fit of Neyman's Contagious Distribution Type A when applied to larvae on pastures is discussed.

3. Examination of permanent pastures over a period of 3 years showed that the difference in time of maximum infestation was greater between fields in the same year than between years for the same field.

4. Counts made on pastures where disease had occurred showed reasonably close agreement with Taylor's estimate.

5. No larvae were detected on fields after ploughing and reseeding.

6. The number of larvae per lb. of herbage on reseeded pastures was low, but the growth of grass masked the fact that the total population was relatively high at the end of the season.

1. An increase in resistance to metachloridine of more than 100-fold was obtained within a few weeks in a strain of Plasmodium gallinaceum treated with gradually increasing doses of the drug and maintained in young chicks by blood-inoculation at intervals of 2–3 days.

2. There was no evidence that the rapid development of resistance arose by the selection of highly resistant individuals present in the normal population.

3. Two strains of P. gallinaceum passaged through chicks treated with 0·025 mg. doses of the drug gradually became resistant to greater concentrations than that to which they had been exposed, though their growth rate decreased when they were inoculated into birds receiving higher doses of the drug.

4. In both strains maintained in birds treated with 0·025 mg. doses of the drug, resistance reached a maximum beyond which it did not increase.

5. Cross-resistance tests failed to show any relationship in mode of action between meta-chloridine and pamaquin, mepacrine, quinine or chloroquine. A strain of P. gallinaceum, highly resistant to metachloridine, showed slight resistance to sulphadiazine, sulphapyridine and sulphathiazole, but none to sulphanilamide or proguanil.

We are indebted to the Cyanamid Products Ltd., London, for the gift of the Folvite used in these experiments.

Pristotrema manteri n.g., n.sp. is described from the spiral valve of the shovel-nosed sturgeon, Scaphirhynchus platorhynchus (Rafinesque), in the Wabash River, Indiana, U.S.A.

A new genus, Pristicola, is erected for Dihemistephanus Little, 1930, nec Looss, 1901, with Pristicola sturionis (Little) as the type and only species.

The subfamily Deropristiinae Cable & Hunninen, 1942, is re-defined to receive the genera Pristotrema and Pristicola as well as the type genus, Deropristis.

The uncertain family position of the Deropristiinae is discussed without removing it from the Lepocreadiidae, although the independent status of that family may be questioned in the light of recent work.

1. Large numbers of Plagiorchis (M.) megalorchis n.nom. were found in the intestine of four turkey poults of a total of thirteen which had died on a farm in Radnorshire. Presumably the presence of the parasites was the cause of death.

2. The anatomy of the adult worm is described.

3. The first intermediate host of the parasite is Lymnaea pereger, and the second intermediate host any of the following species of insect larvae: Chironomus riparius Meigen, Culicoides stigma Meigen, Culicoides nubeculosus Meigen and Anatopynia (Psectrotanypus) varius Fabr.

4. The larval stages of the worm are described.

5. The life cycle has been demonstrated experimentally by the feeding of insect larvae containing encysted cercariae to turkey poults.

6. The turkey is probably not the normal host of Plagiorchis (M.) megalorchis. It is most likely that it occurs naturally in some species of wild bird, but this is not yet known.

During June 1951 a quantity of eggs of the privet hawk moth were obtained in Cambridge. On emergence from the egg it was noticed that a number of the young larvae had died, some immediately after emerging, others after a period of a few days. In some cases the young larvae died before they had got completely clear of the egg shell. Examination of these larvae showed that all had died of a polyhedral virus disease.

The larval stage of Taenia taeniaeformis, namely, Cysticercus taeniae-taeniaeformis, has recently been described by the writer (1951), a detailed account being given of the musculature and of the excretory and nervous systems of the scolex and strobila. In addition, some abnormalities in structure were noted, chief of which was the spiral torsion observed in some specimens and which involved the musculature, excretory and nervous systems of the strobila but not the surface layers. A search was then made for some adult specimens in order to find whether the same abnormality could be seen and to ascertain what the effect of such a torsion would be on the genitalia in the mature and gravid regions. Several adult specimens, from the intestine of a cat, were given to the writer by Mr L. E. Hughes, veterinary investigation officer. Unfortunately, none of these specimens showed the identical spiral torsion found in the larva, but two of them had become knotted together, presumably at an early stage, and were considerably distorted in the regions involved in the knot. This distortion was again of a spiral nature but involved the entire proglottid and not only the internal structures as was found in the type of spiral torsion common in the larval stage of this species. The condition was not merely a turning over of the strobila but an abnormal spiral growth brought about by the continued constriction on the body where the two worms were twisted around one another. So here again, in the adult stage, spiral torsion is evident but from a different cause and involving the whole of the relevant segments from the surface layers to all the contained organs.

In June 1946, one male and one female helminth of the species Marshallagia marshalli (Ransom, 1907) were collected from one of two goats (Capra sibirica), at Manali, which had been slaughtered soon after their arrival from Spiti (Kangra district, Punjab, India). The abomasa, small intestines, lungs and livers of both the animals were available for examination. The lungs, livers and small intestines did not yield any helminths, but one male and one female of Marshallagia marshalli, were collected from the abomasum of one goat, and a single male specimen of Haemonchus contortus was collected from the abomasum of the other goat.

The description of one new species of Ascodipteron and another one of Nycteribosca is based on the material collected in Africa and Madagascar respectively by Mr H. Hoogstraal, of the United States Naval Medical Research Unit No. 3. These specimens represent a part of the collection which was sent to me for identification by Mr R. L. Wenzel of the Chicago Natural History Museum. In this paper I have also included the description of another new species of Ascodipteron of which two specimens were collected by Mr T. S. Jones in West Africa.

Three species of Listrophorid mites representing two genera, Alabidocarpus and Labidocarpus, are known from the European horse-shoe bat Rhinolophus ferroequinum, and one species of Alabidocarpus, A. nasicolus, has already been described (1938) from the closely related Natal horseshoe bat Rhinolophus geoffroyi zuluensis.

Of the fifteen valid species of mammalian blood-flukes so far known, six have been originally described from India. Montgomery (1906) described Schistosoma indicum, S. spindalis and Ornithobilharzia bomfordi (Montgomery, 1906) Price, 1929. Datta (1932) found that nasal granuloma of cattle is due to a new schistosome, which was subsequently obtained and described as Schistosoma nasalis by Rao (1933). Rao & Ayyar (1933) obtained a new schistosome from pigs and described it as S. suis. Mudaliar & Ramanujachari (1945) described S. nairi n.sp., from an elephant, which was transferred to the genus Ornithobilharzia by Bhalerao (1947). Another new species of blood-fluke has now been found in Indian buffaloes and cattle. While studying the larval trematode fauna of the local aquatic snails, large numbers of a new schistosome cercaria were obtained from nine out of three hundred specimens of Limnaea luteola examined during November 1950. When the cercariae were administered to two guinea-pigs, a buffalo-calf and a bull-calf, they developed into an interesting blood-fluke referable to the genus Ornithobilharzia Odhner, 1912. Subsequently, three out of thirteen buffaloes examined post-mortem were found to be naturally infected with the same parasite. The morphology of the adult and of its cercaria is briefly described in this paper.

The identification of Ixodes frontalis Panzer, 1795, from earlier descriptions presented great difficulty, more particularly as the species is rare. There are two specimens in the British Museum (Natural History), and the description by Schulze (1933) is from a single specimen in the Sofia Museum. The rarity of the species led Schulze to write that ‘Die Art ist in Deutschland seit den Zeiten Panzers nicht mehr wiedergefunden worden’. Senevet (1937), who considers I. frontalis synonymous with I. brunneus Koch, 1844, wrote that the species occurred in St Genies-de-Malgoires in France, but this information was taken from Nuttall, Warburton, Cooper & Robinson (1911).

During the course of an investigation into the host-relationship of Ixodes hexagonus Leach a large number of birds was examined for its occurrence. These all proved negative for this species, but I. passericola Sch. was present on one robin out of 220 examined, on one starling out of eleven, on seventeen great tits out of 163, on twenty blue tits out of 540, and on four nuthatches out of fifty. A detailed report on this aspect is given later.