The mites of the subfamily Trombiculinae are of special importance since, in the larval form, they are reported from many countries to be a nuisance to human beings by the intense irritation caused by their bites. At least two species of these larvae are the acknowledged vectors of scrub typhus (OXK typhus, ‘tsutsugamushi’ or Japanese river fever). The nymph and adult mites are free living and are known to be predatory, feeding upon the collembola and also on the eggs of ants, mosquitoes and collembola. In the larval stage they are found as parasites on mammals, birds, snakes, lizards and frogs. They have also been recorded upon a scorpion and upon three families of grasshoppers.

A new species of Rhipicephalid tick, Rhipicephalus hurti, is described from game animals from the Rift Valley of Kenya. The new species is compared with R. capensis, R. serranoi and R. jeanneli.

My thanks are due to Dr G. Theiler, Onderstepoort, who confirmed that R. hurticould be correctly regarded as a new species and has been most generous in her assistance. My thanks are also due to Dr Santos Dias and Dr Hoogstraal for their most helpful criticisms; to Lieut.-Col. Hurt for his interest and care in sending me numerous tick-collections from the Naivasha area of Kenya; to Mr Alex Wiley and Mr Guggesburg for their careful drawings; and to Miss Walker, E.A.V.R.O., and my colleague Mr Pollard, for their generous help at all times.

The whole life cycle of Paramphistomum microbothrium Fischoeder, 1901, found in cattle of Kenya, East Africa, has been established experimentally.

In laboratory conditions, the eggs hatched miracidia on the 14th to 16th day, if they were kept in water at a temperature of 26–28° C.

In a snail, Bulinus alluaudi (Dautzenberg), kept at the temperature of 18–20° C., the miracidium developed into a sporocyst, the elongated body of which, containing young rediae, reached a length of 3·6 mm. in about 2 weeks.

The first rediae which emerged from a sporocyst were observed on the 14th day, and on the 20th day the first generation rediae began to produce second-generation rediae. From the 28th day onward the first-generation parent rediae ceased to produce daughter rediae and began to develop cercariae only. This period of production of cercariae by the redia lasted about 30 days, and when the life of the first-generation rediae drew to its close, the old rediae developed a few daughter rediae again.

Cercariae began to emerge from the first-generation rediae 30 days after exposure of the snail to miracidia. The cercariae left the parent redia in a very immature state and further development occurred in the liver of the snail. The emergence of cercariae from the infected snail began on the 43rd day after exposure to miracidia. Shortly after emerging from the snail, the cercariae attached themselves to vegetation and encysted.

Development of rediae of the second, third, fourth and apparently more successive generations followed an identical course to that outlined for the rediae of the first generation. As a result the successive generations of rediae maintain the infection going in an intermediate host and the infected snails were continually shedding cercariae as long as they lived. In the laboratory experiments the life span of some of the infected snails exceeded a year.

In cattle infected experimentally P. microbothrium reached maturity and began passing out the eggs about a 100 days after the encysted cercariae were fed to the animals.

1. On the assumption that the limit of significant difference is 1%, it is necessary, when concentration methods are not used, to repeat the faecal examination 3 times for the egg of Ascaris lumbricoides, 7 times for hook worm and 11 times for Trichuris trichiura in order to obtain the diagnostic results obtained by the acid-ether concentration technique using 3 g. of faeces.

2. The coefficient of the identification by a single smear examination is 83·3% for eggs of Ascaris lumbricoides, 46·5% for hook-worm eggs and 33·6% for eggs of Trichuris trichiura.

1. A technique is described for the laboratory breeding of Musca domestica nebulo Fabr. the Indian house-fly.

2. Methods are described for the transferring of the flies from cages to appliances for testing insecticides and for close observation.

I am very thankful to Mr E. B. Raj-der-ker who kindly donated the B. K. Raj-der-ker insect breeding station for our work. I owe a debt of gratitude to the authorities of the Indian Law Society, Poona, who have placed land and building facilities at our disposal for this research. Prof. S. P. Agharkar placed all the facilities of the Research Institute of the Maharashtra Association for the Cultivation of Science at my disposal, and Mr D. R. Ranade voluntarily supervised the breeding at Poona.

The most conspicuous feature of the spiracle of Ornithodoros moubata is the so-called cribriform plate. This is a massive crescent-shaped vesicle consisting of three layers; the underlying sclerotized endocuticle, a series of branching pillars or pedicels arising from this basal layer and a very thin outer membrane, supported on the distal ends of the pillars and enclosing the whole structure (Fig. 1 A). The cavity lying between the basal cuticle and the outer membrane and ramifying between the pillars is continuous with the atrium of the spiracle.

1. Methods of sampling pastures for infective larvae are discussed.

2. An account is given of the methods of operation and identification of larvae from herbage.

3. The distribution of larvae on pastures is discussed in relation to choice of method of sampling and interpretation of results.

4. The significance of grazing patterns to distribution of larvae is considered.

5. An attempt is made to evaluate the use and limitations of pasture sampling methods.

The author is indebted to the Agricultural Research Council for financial assistance in the form of a special research grant.

T. genypteri n.g., n.sp., is described from the stomach of the red ling, Genypterus blacodes Bloch & Schn., in coastal waters of Otago, New Zealand. This genus is characterized by having a small sucker anterior to the oral sucker and two muscle pads in the forebody.

The specimens described in this paper were collected in Assam by Dr M. L. Roonwal during World War II, and were sent to me for identification by Dr S. L. Hora, Director, Zoological Survey of India.

I am grateful to Prof. H. R. Mehra, Professor of Zoology, Allahabad University, for his able guidance, to Dr Hora for sending me the material and to Dr Charles D. Radford for his opinion on the species described in this paper.

1. In intact rats infected with P. berghei spontaneous eradication of infection has occurred by about 4 months after the day of inoculation.

2. These recovered rats show a strong residual immunity to reinfection with a heterologous strain, but this has begun to wane by 15–18 months after cure of the initial infection.

I owe many thanks to Miss W. J. Wall and Miss J. Wrugh of the Ross Institute for maintenance of the rats and assistance with the blood films.

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. 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.

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.

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 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.

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).