Dujardin (1835) was the first to describe an adult gregarine occurring in an earthworm. This description contains illustrations of a typical Nematocystis species (Dujardin's Text-figs. B1-B7 and C1 and C2). Subsequent workers made many other observations, but it was Hesse (1909) who first carried out a comprehensive study of these parasites. It was Hesse's excellent work which laid the foundation for succeeding students of the group, the more important of whom are Cognetti de Martiis (1911, 1918, 1920, 1921, 1923, 1925, 1926, 1927), Berlin (1923, 1924), Bhatia (1924, 1924b, 1929, 1930), Bhatia & Setna (1926), Setna (1927), Bhatia & Chatterjee (1925), Troisi (1933, 1940), Tuzet & Loubatières (1946, 1948) and Loubatières (1947, 1948, 1949). Hesse gave a good historical resumé of the work carried out until 1909, while Loubatières (1949) has given a complete and very useful resumé of the work since.

The genus Hysterocineta Diesing, 1866, is a small genus comprised, until the present description, of only four species. Together with the genus Ptychostomum Stein, 1861, it forms the family Hysterocinetidae Diesing, 1866, which is a constituent family of the suborder Thigmotricha Chatton & Lwoff, 1949. The holotrichous ciliates belonging to this genus are characterized by the possession of elongate, flattened, flexible bodies possessing an inverted V- or U-shaped sucker at their antero-ventral margins, and a cytostome and cytopharynx at the posterior end.

In this paper three new species of the genus Allocreadium Looss, 1900, viz. A. dollfusi sp.nov., A. singhi sp.nov. and A. hirnai sp.nov. are described. These parasites were obtained from the intestine of the fish Barbus tor (Ham.) brought from the River Hiran. A number of specimens of this species of fish were several times examined for helminth parasites at Katangi, 24 miles from Jabalpur and at Sihora, 25 miles from Jabalpur. These parasites were recovered from different individuals of the fish B. tor (Ham.).

1. The mouse and rat (an abnormal host) show an age resistance towards experimental infections with N. dubius.

2. This resistance was complicated by a different reaction in the male and female mouse and rat.

3. The rat exhibits age resistance despite being gonadectomized immediately after weaning.

4. Gonadectomy with replacement of the homologous sex hormone did not materially alter the age resistance of the host, but the administration of testosterone to the castrated male rat increased the numbers of larvae which penetrated the gut wall. Oestradiol decreased these numbers in the spayed female rat.

5. The relationships between the age resistance and the sex resistance of the hosts was discussed.

1. The mouse is more susceptible to infection than the rat.

2. The male in both the rat and the mouse is more susceptible to infection than the female.

3. The development of the worm is slower in the male rat than in the female. This relationship does not occur in the mouse.

4. The ecological position of the adult parasite was different in the mouse and rat, the worms living further down the intestine in the rat.

5. The effects of host species on infection of N. dubius are discussed.

Representatives of a total of twenty fish species, most of them marine, from the Black Sea coast in Rumania were investigated. Of these, ten species were found to harbour ectoparasitic trichodinids on their skin and gills. Three of them, Trichodina rectuncinata Raabe, 1959, from Gaidropsis mediterranaeus and Crenilabrus griseus, T. caspialosae (Dogiel, 1940) mihi from Alosa braschnikowi meotica and T. d. f. latispina from Gasterosteus aculeatus, were already known.

Three species could be established as new ones: T. puytoraci sp.nov. from Mugil auratus, M. cephalus and M. saliens, T. raabei sp.nov. from Pleuronectes flesus and T. lepsii sp.nov. from M. auratus. They are clearly differentiated from other species.

The following trichodinids were provisionally classified as forms (including one new one) of T. domerguei, thus enlarging this most complicated Trichodina species: T. domerguei, cf. latispina from Gobius syrman, T. domerguei f.n. maris-negri from Gaidropsis mediterranaeus, and T. domerguei f. partidisci from Mugil cephalus. Other populations of T. domerguei could not be properly classified because of lack of material.

The description of the new species of Tripartiella which have been mentioned in the introduction, will be given in a separate paper.

A short survey on marine trichodinids recorded up to the present is given.

It was found that Lucilia porphyrina Walker lays eggs on living toads (Bufo melanostictus). Larvae hatched out of the eggs in about two days and attacked the region of the upper eye-lids of the toads, where a lesion was produced. The parotoid gland was sometimes attacked. The larvae also infested the sites of injuries on the toads.

The toads thus attacked soon died and the larvae fed on their dead tissues. Mature larvae came out of the carcass within a few days and entered the soil, where they pupated. The adult fly emerged after about 20 days.

A description is given of the external features of the scolex and strobila and the anatomy of the proglottid of Acanthobothrium pearsoni sp.nov. found in the intestine of Orectolobus maculatus Bon. In view of the similarity in host distribution and anatomy to that of Biporophyllaeus madrassensis Subramanian some comments are made on the status of the order Biporophyllaeidea and it is suggested that B. madrassensis may be a proglottid of a species of Acanthobothrium.

1. The development of S. duttoni and S. recurrentis was studied in lice.

2. After penetrating the anterior part of the midgut spirochaetes were seen in the haemocoele, haemocytes, neural ganglia and muscles of lice. They were never seen elsewhere.

3. The haemocytes of infected lice sometimes contained coarse granules believed to be the breakdown products of spirochaetes due to phagocytosis.

Young chickens given an infection of 5000 oocysts of E. maxima were highly resistant when they were given a 2nd dose 3 weeks later. Immunity in these fowls was not apparent when they were again infected 10 weeks after the 2nd infection. The same fowls given a final dose 26 weeks after the 3rd infection became heavily infected. These observations suggest that immunity developed to this infection is short-lived, and this finding is discussed in relation to the duration of acquired immunity to E. tenella infection in the fowl and E. stiedae infection in the rabbit.

1. Frogs were collected from a single area in the West Riding of Yorkshire and examined for adult helminth parasites. The following species were found: Polystoma integerrimum, Gorgoderina vitelliloba, Haplometra cylindracea, Dolichosaccus rastellus, Rhabdias bufonis, Cosmocerca ornata, Oswaldocruzia filiformis, Aplectana acuminata and Acanthocephalus ranae.

2. The seasonal incidence and intensity of infection was studied by monthly examinations of 2413 frogs over a period of 4 years. The highest incidence of parasitization by helminths occurred in the autumn. In general, when the incidence was high, the intensity of infection was also high.

3. The incidence of infection was generally higher in male than in female frogs. This effect of the host's sex was much more marked immediately before the breeding season than at any other time of the year.

4. Possible reasons for these variations in levels of infection are discussed.

1. The pseudosuckers and holdfast organ of the metacercaria and adult stages of Diplostomum phoxini do not secrete acid mucopolysaccharide.

2. Alkaline phosphatase is present in the holdfast organ and in the cuticle lining the holdfast organ but not in the forebody glands or pseudosuckers.

3. Non-specific esterase has been shown to be present in the metacercaria and adult, especially in the pseudosuckers, the forebody glands which supply the pseudosuckers and in the holdfast organ. There is very little non-specific esterase in the posterior lobe of the adult.

4. Results of tests with enzyme inhibitors have shown that there are probably both A-esterase and B-esterase in the pseudosuckers, forebody glands and holdfast organ and that there is a cholinesterase present in the nervous system.

5. Cystine is present in most of the cuticle of the metacercaria but is absent from the cuticle lining the holdfast organ and the pseudosuckers.

6. The pseudosuckers and forebody glands as well as the holdfast organ appear to play a part in extracorporeal digestion.

1. Factors controlling the distribution of the bird fleas Ceratophyllus styx, the sand-martin flea, C. gallinae, the hen flea, and Dasypsylla gallinulae, the blackbird flea, were investigated in the field.

2. Sand-martin fleas (C. styx) pass the winter as adults within cocoons in the old nests of their host. Observations indicate that the fleas are stimulated to emerge from the cocoons by the rise in temperature in the spring, and some of the adult fleas emigrate in the spring and invade new nest burrows. Observations and experiments showed that sand-martin fleas disperse from old burrows both laterally and vertically and that emigrating fleas could reach areas as far as 33·8 m. from the old nests. The detection of the new burrow entrances is not due to vision, or to the recognition of difference of humidity between the burrow and the cliff face, or to the reaction to air current differences between the burrow and the cliff face, but to recognition of the horizontal floor of the burrows and a tendency to congregate upon horizontal surfaces. How the fleas distinguish the horizontal burrow surface from the cliff top is still unknown. The colonization of new burrows by the fleas does not occur at night. It is suggested that, in addition to finding their hosts in the spring by invading new burrows, sand-martin fleas may jump on to the birds when they are hovering near the cliff face. Many adult fleas leave the burrows within 3 days of the fledging time of the young sand-martins but a small number remain within the nest. The fate of these specimens is not known.

3. C. gallinae, the hen flea, and D. gallinulae, the blackbird flea, pass the winter principally as adults enclosed in the cocoons in the old nest material. In the spring they emerge from the cocoons, emigrate away from the old nest and are free-living on the ground. Probably the adult C. gallinae and D. gallinulae jump on to birds when they are feeding on the ground in the spring.* Therefore the absence of hen fleas in nests situated on the ground or in open nests built in low vegetation, is not due to lack of opportunity of contact between the adult flea and the birds which construct such nests.

4. It is concluded that in host-seeking, adults of C. gallinae and D. gallinulae emigrate away from old nests in the spring and come in contact with the host birds on the ground in the birds' feeding area, whereas C. styx adults emigrate into the hosts' breeding area and come in contact with the birds in the new nesting burrows.

1. The spermatophore of the argasid tick Argas persicus, is a sac enclosing a mass of sperm and a number of other structures which are rapidly extruded into the vagina of the female tick during copulation.

2. During copulation the first part of the contents of the spermatophore to be extruded consists of a clear tip with two lateral semi-opaque areas surrounded by white borders and a mass of opaque white material followed by the sperm.

3. The male accessory reproductive gland is redescribed. It consists of a stem portion which gives off: dorsally, the unpaired anterior dorsal granular lobe and the paired posterior dorsal and third lateral granular lobes; the small paired second lateral granular lobes from the mid-region; ventrally, the small unpaired median granular lobe and the large paired first lateral granular lobes and, opening into the ejaculatory duct, the small, paired anterior and posterior spongy lobes.

4. The anterior and posterior spongy lobes secrete an acid mucopolysaccharide which thinly coats the spermatophore.

5. The median granular lobe secretes a phospholipoprotein rich in phenolic groups and a polyphenol oxidase.

6. The first lateral granular lobes secrete a basic protein which interacts with the secretions of the median granular lobe to form the main wall of the spermatophore.

7. The second lateral granular lobes secrete the tenuous mucoprotein membrane which surrounds the sperm mass within the spermatophore and also the large protein granules which adhere to the inner surface of this membrane.

8. The third lateral granular lobe secretes the mass of opaque, white material in the spermatophore; possibly this is pharmacologically active and analogous to the secretion of the opaque glands of Rhodnius.

9. The posterior dorsal granular lobes secrete a non-specific esterase at their tip and a protein in the mid-region; these form, respectively, the lateral semi-opaque areas and their white borders in the spermatophore.

10. The anterior dorsal granular lobe secretes an acid mucopolysaccharideprotein complex which forms the clear tip of the extruded contents of the spermatophore.

Paramphistomum daubneyi sp.nov., recovered from Bos taurus in Kenya, East Africa, is described and differentiated from the other species of the genus possessing a Microbothrium type of genital atrium.

Lymnaea truncatula Müller was infected experimentally with miracidia of P. daubneyi and the development in the snail host is briefly described.

There is histochemical evidence for the presence of calcium, glycogen, simple proteins and alkaline phosphatase in the calcareous corpuscles occurring in the parenchyma of Taenia saginata. A distinct Feulgen-positive reaction is seen in most of these corpuscles. The material yielding this positive reaction is apparently derived from the nucleus of certain mesenchymal cells from which these corpuscles supposedly originate. In some corpuscles, which are probably at the early stage of formation, the nucleus of such a mesenchymal cell is clearly seen adhering to the surface of the corpuscle. The identity of the nucleus of such cells is apparently lost in the fully formed corpuscle. Each corpuscle has a concentric appearance and is probably formed in successive layers.

Two new species of Giardia are described: G. wenyoni sp.nov., from the duodenum of slender loris, Loris tardigradus lydekkerianus, and G. dasi sp.nov. from the duodenum of palm-civet, Paradoxurus hermaphroditus hermaphroditus.

The distinguishing features of G. wenyoni are (measurements in microns): range of length 12·0–20·0, average 15·6; range of breadth 5·5–11·5, average 8·8; ratio of length to breadth 1·7; distance from anterior end to centre of nucleus 4·5; centre of nucleus to ends of lateral shields 7·0; ends of lateral shields to posterior end 3·6; breadth across centre of nucleus 7·7; length of the sucker 6·2; the ratio of body length to the length of sucker 2·5. The nuclei do not lie parallel to the axostyles. Each nucleus contains chromatin granules along the periphery.

G. dasi is distinguished by its dimensions which are (in microns): range of length 11·8–20·0, average 15·5; range of breadth 5·0–12·5, average 7·2; ratio of length to breadth 2·1; distance from anterior end to centre of nucleus 4·7; centre of nucleus to ends of lateral shields 6·0; ends of lateral shields to posterior end 5·4; breadth across the centre of nucleus 6·6; length of the sucker 6·0; the ratio of body length to length of sucker 2·5. Chromatin granules are present in the form of a ring in the centre of the nucleus. The most characteristic feature of this organism is the presence of certain large granules in the cytoplasm.

Retortamonas cheloni sp.nov., from the large intestine of the starred tortoise, Testudo elegans Schoepff, 1792, is described. Body oval with a long caudal process; length of body 4·2–11·5μ, 7·9 average; breadth 3·0–6·5μ, average 4·4; length of caudal process 1·0–7·0μ, average 4·0. Nucleus round, situated at the extreme anterior end, with a thin ring of chromatin adjacent to the nuclear membrane and sometimes an endosome. Cytostome deep, extending one-third to one-half of the body-length and bordered by two siderophilic threads. Close to the nucleus are two blepharoplasts from which arise two unequal flagella and the two siderophilic threads. Periplast rigid.

During August 1953, the Hon. Miriam Rothschild, with the assistance of Dr Schifferli and Fritz Muhlethaler, succeeded in obtaining three nests of the Alpine chough Pyrrhocorax graculus L. on the Niesen (1200 m.) Bernese Oberland, Switzerland. Three nests of the snow finch Montifringilla nivalis L. were collected during the same period from behind gutters and under eaves on the railway buildings at Eigergletscher (2320 m.), Bernese Oberland, immediately after the young birds had flown.

Five new species of Myxosporidia are described and figured. They are: Ceratomyxa auerbachi, Davisia longibrachia, Myxidium laticurvum, Parvicapsula unicornis and Sphaerospora irregularis. The first two are parasitic in the gall-bladders, while the remaining three in the urinary bladders of various teleosts in the North Sea.