The action of pyrimethamine, sulphadiazine, proguanil and its active metabolite CPT, and 2:4-diaminopteridines against infections of Plasmodium berghei in mice was antagonized by P–aminobenzoic acid and by pteroylglutamic acid. Antagonism was in some instances detected only when P–aminobenzoic acid was given in solution in the drinking water as well as being injected subcutaneously. No antagonism was detected with a number of amino acids and nucleic acid derivatives.

As all of the above group of drugs can be antagonized by P–aminobenzoic acid and by pteroylglutamic acid, it would seem that they are alike in their mode of action. There must, however, be some differences between the mode of action or absorption of these drugs because species of Plasmodium that are very sensitive to the action of one of these drugs are frequently not very sensitive to the action of others.

As P. berghei is dependent on p–aminobenzoic acid, it is suggested that it can utilize this compound in the synthesis of pteroylglutamic acid to a greater extent than can P. gallinaceum, and that it resembles P. knowlesi more than other species of Plasmodium.

In dibacterial cultures of E. invadens the size of the cysts was significantly influenced by different species of concomitant bacteria, and by the composition of the media. These factors appear to influence cyst size as a result of their effect on the growth rate of the amoebae; a higher multiplication rate was associated with a decrease in the size of the cysts.

I wish to thank Dr A. Bishop for criticizing the manuscript, and Mr W. McConnachie, jun., for assistance with the statistical methods. The work has been financed by the Medical Research Council.

1. The feeding habits of second- and third-instar larvae of Neottiophilum praeustum have been observed and show that this species is a true parasite of birds and feeds by sucking the blood of nestlings.

2. If they are too numerous the larvae may kill the nestlings. Although they will continue to feed upon dead birds, and even penetrate into the viscera, such food is unsuitable for the development of the larvae and they become greatly distended and die within a few days.

3. The morphology of the hitherto unknown second-instar larva is described and is compared with that of the third instar.

4. Within the puparium of Neottiophilum praeustum there is a fourth moult resulting in the formation of a cast prepupal cuticle which resembles that described by Snodgrass in Rhagoletis pomonella and is much better developed than the prepupal cuticle in Calliphora erythrocephala.

5. The better development of the prepupal cuticle in the acalypterates than in calypterates indicates that the presence of a prepupal stage in the cyclorrhaphous Diptera is a primitive character and is progressively reduced until in the higher families it is almost vestigial.

1. Hymenolepis diminuta is shown to be quite frequent in the rat, Rattus rattus, of Colombo; and reasons are suggested for its apparent rarity in man.

2. An extremely low incidence of H. nana in rats was found. It is suggested that this cestode will not be found to parasitize man in Ceylon as long as its murine infection continues to be low.

3. Raillietina madagascariensis is not uncommon in rats in Ceylon; but, until its vector has been detected, the possibility that it may infest man in Ceylon cannot profitably be discussed.

4. Instances of variation in the arrangement of genital pores in R. madagascariensis, and in the general anatomy of H. diminuta were detected.

I am grateful to Dr G. A. R. Perera, Medical Officer of Health, Colombo Municipal Council, for supplying the rats used in this study; to Drs V. Sivalingam and L. G. Jayawardena of this Institute for helpful criticism, and to Dr A. C. J. Weera-koon of the University of Ceylon for revising my manuscript.

In strains of Plasmodium gallinaceum passaged by blood-inoculation, through young birds treated with small, but effective doses of proguanil, sulphadiazine or 2:4-diamino-6:7-diisopropylpteridine, the numbers of gametocytes produced were much greater than in the parent strain passaged by the same method.

The effect of the drugs upon gametocyte production appears to be a long term one, since no change in gametocyte numbers was observed in birds treated with proguanil or sulphadiazine for only a few days.

The relationship of these drugs to nuclear division and the synthesis of nucleic acids is discussed in the light of the observed increase in gametocyte-production in drug-treated strains of P. gallinaceum.

1. The bucephalid cercaria from Crassostrea virginica (Gmelin), the commercial oyster of the Atlantic and Gulf coasts of North America, has been called Bucephalus haimeanus Lacaze-Duthiers and Bucephalopsis haimeana (Lacaze-Duthiers). Neither of these names is correct. Bucephalus haimeanus Lacaze-Duthiers, 1854, is a parasite of the European oyster, Ostrea edulis L. (and possibly of cockles, Cardium spp.) in oceanic or near-oceanic habitats, while the American species is a parasite of an estuarine oyster and is found almost entirely in the least saline parts of its host's range. The correct name of the American oyster bucephalid is Bucephalus cuculus McCrady, 1874.

2. The life cycles of all European marine bucephalids are still unknown. The life cycles described in the European literature are based entirely on morphological resemblances which are not close enough to be convincing, and none of them has been tested by experiment. Bucephalid cercariae do not show any of the features which are used to distinguish genera. So far as present evidence goes, Bucephalopsis haimeana is just as likely to develop into a Rhipidocotyle, a Bucephalus, or a Prosorhynchus as it is to develop into a member of the genus Bucephalopsis Nicoll, 1914, nec Diesing, 1855.

3. Bucephalopsis Diesing, 1855, is the name proposed by Diesing for a subgenus created especially for the cercaria Bucephalus haimeanus Lacaze-Duthiers, 1854. Nicoll had no right to use this name for the genus of gasterostomes which, as adults, have a muscular sucker at the anterior end and do not have accessory structures such as a hood or papillae. Up to the present, there is still no evidence that this genus has any connexion with Lacaze-Duthiers's cercaria, other than common membership in the family Bucephalidae. Therefore the new name Bucephaloides Hopkins has been proposed to replace the generic name Bucephalopsis Nicoll, 1914, nec Diesing, 1855, with Bucephaloides gracilescens (Rudolphi, 1819) as the type species. This genus does not include Bucephalus haimeanus Lacaze-Duthiers because the metacercaria and the adult form of that species remain unknown.

4. Tennent (1905, 1906, 1909) did not prove that there was any connexion between the oyster cercaria, Bucephalus cuculus McCrady, and the immature bucephalids in Menidia or the adult bucephalids in Strongylura. His drawings show that at least some of the bucephalids which Tennent studied had a hood and therefore belong in Rhipidocotyle. Re-examination of the bucephalids in Strongylura marina reveals that at least three species of bucephalids occur as adults in that host; these are described in this paper as Rhipidocotyle transversale Chandler, 1935, R. lintoni Hopkins, and Bucephaloides strongylurae Hopkins. Rhipidocotyle transversale and Bucephaloides strongylurae were also found in an immature (metacercaria) stage in Menidia, and were the only bucephalids found in Menidia during this study. The excretory systems of the three species in Strongylura all have features which exclude the possibility that they could develop from the oyster cercaria, Bucephalus cuculus.

5. Tennent's (1906) drawing (fig. 46) of an adult bucephalid from Strongylura marina, which Eckmann (1932) mentions as the best representation of the species characteristics of Bucephalopsis haimeana (Lacaze-Duthiers), was probably made from a specimen of Rhipidocotyle lintoni.

6. Tennent (1909) proved that eggs or larvae from an unknown adult bucephalid in Lepisosteus osseus could infect oysters, Crassostrea virginica, and develop into sporocysts which would grow in oysters for at least one month. This is the only experimental proof of a connexion between an adult bucephalid in a fish and a larval bucephalid in an oyster. Until the present, no bucephalid from a gar (Lepisosteus) had ever been described. In the present paper Rhipidocotyle lepis-ostei Hopkins is described from adults in Lepisosteus spatula, the alligator gar, in Louisiana. The metacercariae of Rhipidocotyle lepisostei are abundant in the fin rays of mullets, Mugil cephalus and M. curema. The excretory system of this species is not identical with that of Bucephalus cuculus, but is not so different as to exclude the possibility that the oyster cercaria might develop into R. lepisostei. If, in the future, R. lepisostei is proved to be the adult form of Bucephalus cuculus, the name of the species will become Rhipidocotyle cuculus (McCrady), and R. lepisostei will become a synonym.

1. A method, based on that devised for E. histolytica by Dobell (1947), was worked out for testing the action of drugs upon E. invadens.

2. The sensitivity of di- and monobacterial strains of E. invadens to emetine was determined, and of a dibacterial strain to the quinaldines A 352, A 356 and A 404. E. invadens was killed by emetine at concentrations of 1/50,000–1/100,000, A 352 or A 356 at 1/100,000, and A 404 at 1/10,000. The strains of E. invadens used in the present tests are thus less sensitive to emetine than is E. histolytica, but the sensitivity of the two species to the quinaldines is similar.

3. A strain of E. invadens which was maintained for 9 months in the presence of increasing concentrations of emetine, did not become resistant to the drug.

I am indebted to Dr A. Bishop for much advice and criticism; to Dr J. D. Fulton for a culture of Bacterium coli A'; and to Dr J. Walker for supplies of the compounds A 352, A 356 and A404. The work has been financed by the Medical Research Council.

The choniostomatids parasitic on Crustacea have been exhaustively studied by Hansen. To the six genera and forty-three species he had described in 1897, he added a new genus and three more species in 1904, and seven more species in 1923. Scott (1904, 1905, 1907) described seven more species, Fraenkel (1915) three new species, Monod (1930) one, and Blake (1929) two. In 1929, however, Connolly described a new genus Choniosphaera and its type species C. cancrorum, from parasites found on American crabs Cancer amoenas, C. irroratus and C. borealis. In the present paper a new species Choniosphaera indica, parasitic on the edible crab Neptunus sanguinolentus of Madras, is described.

The genus Ischnopsyllus Westwood, comprising at the moment sixteen species and subspecies, is rather a heterogenous group. Although I am reluctant to split this relatively small genus, a certain degree of division is unavoidable. First, I. grahami Waterston certainly does not belong to the genus Ischnopsyllus, and since this species does not fit any other genus of bat-fleas, a new genus has had to be erected for it (see below, where a new subspecies of grahami is also described). Secondly, the hexactenus-group of Ischnopsyllus is sufficiently distinct from the rest of the genus to make it desirable to restore, as a subgenus, the genus Hexactenopsylla Oudemans, which was synonymized with Ischnopsyllus by Dalla Torre in 1924.

The copepod described in this paper has been found in Strangford Lough, Co. Down, an area which has already proved rich in ascidicolous copepods of the suborder Notodelphyoida (Gotto, 1952). The present species, however, belongs to the section Poecilostoma of the suborder Cyclopoida, many members of which are associated with marine animals of several different groups. The extremes of retrogressive specialization which characterize many of the notodelphyoids are not, on the whole, so apparent in these cyclopoids, their associative habits often being inferred from general structure rather than proved occurrence with any particular host. Thus a fair number of the types described have been found unattached in dredged material, the possible host being any one of several species taken in the same haul. Associations of an apparently loose nature are therefore sufficiently frequent to render the present form of particular interest since it has so far been found exclusively in the compound ascidian Trididemnum tenerum (Verrill), in which it is localized in the extensive cloacal cavities. Further search may of course reveal alternative hosts, since the family Lichomolgidae, to which it undoubtedly belongs, has a wide range of acceptable hosts. Indeed the genus Lichomolgus is known to occur in association with sponges, polychaets, nudibranchs, gasteropods, cephalopods, holothurians and ascidians—and one species, L. agilis (Leydig) has been recorded from a score of different nudibranchs.

In connexion with studies on bat malaria carried out by Prof. G. Mer and Dr N. Goldblum at the Malaria Research Station of the Hebrew University, a great number of ectoparasites of bats were submitted to us for identification. Together with material collected by us, over a thousand nycteribiids, streblids, Hemiptera, Siphonaptera, ticks and mites were examined.

Among the principal intestinal factors that play a part in the host-parasite relationships, the pH values of the parasite's habitat within the host under various conditions are of great significance. As stated previously (Haiba & Williamson, 1952), among the intestinal Protozoa of man and animals, Giardia is of much interest owing to its selective localization on the inner epithelial surface or occasionally inside the goblet cells of the upper two-thirds of the small intestine, representing an important area where the main maximal intestinal functions are carried out. Accordingly, the pH of the intestinal wall, as distinct from that of the contents, is likely to be a pertinent environmental factor in giardial infections.

The morphology and life history of a new species of insect-parasitic nematode, Neoplectana leucaniae are described. This nematode, which may be cultured on a veal pulp medium, was used in a number of experiments against larvae and adults of New Zealand Melolonthinae, and was found capable of parasitizing all test hosts used. Lack of persistence of the nematode in soil makes it unsuitable for use in the biological control of soil-inhabiting pest insects.

It has recently been shown (Smith & Wyckoff, 1950) that, in addition to the classical type of nuclear polyhedral disease of lepidopterous larvae, there exists a second type of polyhedrosis with spherical virus particles instead of rods. This was demonstrated in the case of two tiger-moth larvae, Arctia villica and A. caja. The polyhedra of this type of disease do not dissolve fully when treated with weak alkali but leave behind a honeycomb-like shell pitted with round holes. We have also shown (Xeros, 1952, Smith & Xeros, 1953a) that in all our material these polyhedra occur in the cytoplasm and not in the nuclei and are confined to the cells of the midgut.

1. Different extracts of adult worms of S. mansoni and F. hepatica have been examined in the C.F.T. for bilharziasis. Extracts of S. mansoni worms in Coca's solution, alcohol-ether and absolute alcohol after acetone extraction possess high antigenic activity, the first being the most specific but less sensitive than the others. Extracts in Coca's solution of alcohol-ether insoluble residues still showed slight activity while acetone and polysaccharide (formamide) extracts showed none.

2. Using the Coca's extract of S. mansoni worms, the C.F.T. was positive in 83% of sera of untreated patients and 58% of treated. The figures using the alcohol-ether extract were 13 and 4% respectively and, for the alcoholic extract of acetone insoluble residue, 42 and 13%.

3. Extracts of F. hepatica worms showed the same general trend, but even in the two extracts to show activity (alcohol-ether and alcohol extract of acetone insoluble material) the titre was too low for use in the test.

4. Of rabbits immunized with three different fractions of S. mansoni worms only that given the Coca extract showed complement-fixing antibodies and then only with the homologous antigen. Skin tests on the rabbits were negative to each of the antigens used.

5. The nature of the antigen in the C.F.T. is discussed, and it is suggested that the active portion is lipo-protein in nature or more than one substance is involved. For use in clinical diagnosis, an extract of S. mansoni worms in Coca's solution is recommended.

Our grateful thanks are due to Mr O. D. Standen of the Wellcome Laboratories of Tropical Medicine, London, for his generous gift of worm powder, and to Professor G. Witenberg of the Hebrew University for his interest in our work.

Paramphistomumi sukari n.sp. from the reticulum of cattle in the Kenya Highlands (East Africa) is described. An intermediate snail host of P. sukari was shown to be Biophalaria pfeifferi (Krauss).

1. The morphology of an Entamoeba from the Sudanese lizards Mabuya quinquetaeniata, M. striata and Tarentola annularis is described. It was similar to Entamoeba coli of man.

2. It is referred to the species E. flaviviridis, Knowles & Das Gupta (1935).

3. An ‘Amoeba’ was observed in Tarentola annularis which was similar in size to the Entamoeba. The nuclear structure, however, was distinctive, with a very large karyosome and no peripheral chromatin. The cysts were uninucleate.

4. It is very similar to the organism described as Vahlkampfia reynoldsi by McFall (1926).

1. It has been shown by spectroscopic and histochemical methods that eight representative species of Polyopisthocotylea feed mainly on the blood of their hosts.

2. The blood is probably haemolysed fairly rapidly and subsequently absorbed by amoeboid ingestion, the globin moiety of the haemoglobin forming the chief nutriment of the parasite and the unaltered haematin being eliminated either by its discharge from epithelial cells into the gut lumen or by the sloughing off of intact epithelial cells.

3. In a more limited sample of skin-and cloaca-inhabiting Monopisthocotylea there was no evidence of a blood-feeding habit.