1. Studies on two Microsporidia, Nosema helminthorum Moniez and N. locustae Canning, have shown that the polar filament serves to conduct the sporoplasm out of the spore.

2. The filament is a solid structure and the sporoplasm is either attached to or is a continuation of it. The filament is first extruded as a tightly coiled mass and, as this uncoils, it drags the sporoplasm out of the spore.

3. The sporoplasm, which is either uninucleate or binucleate, takes the form of a girdle of protoplasm, which lies on the inner side of the spore membrane and surrounds the coiled polar filament. There is no polar capsule.

1. Metacercariae are recorded from the kidney tissues of slugs. Over 3000 slugs belonging to ten species were examined. Infection was confined to Milax sowerbii (Férussac) and Agriolimax reticulatus (Müller) apart from a few infected specimens of Arion ater (Linnaeus) or A. lusitanicus Mabille. Only one sporocyst was discovered and this occurred in A. lusitanicus.

2. Four distinct stages in metacercarial development are described—the caudal stage (0·7 × 0·3 mm.), the feeding stage (0·9 × 0·5 mm.), the corrugated stage (1·3 × 0·7 mm.) and the mature metacercaria (2·5 × 1·0 mm.). The corrugated stage is so-named because of the distinctive appearance of its cuticle.

3. Both the cercaria and metacercaria belong to the genus Brachylaemus (Dujardin, 1843) Blanchard 1847 and they probably belong to the same species. Since the life history is not known, no trivial name has been given to the organism.

This work was carried out with a strain of trypanosomes isolated by inoculation into domestic rabbits of fleas naturally infected from wild rabbits in Hertfordshire.

The course of infection was studied in experimentally infected normal and splenectomized rabbits, in which the incubation period varied from 5 to 12 days. After recovery from the infection, rabbits became immune to re-infection. Immune rabbit serum had no protective action against Trypanosoma lewisi.

Attempts to infect other animals with the rabbit trypanosome produced negative results.

Young rabbits proved to be more susceptible to infection with this trypanosome, and their parasitaemia lasted longer than in adult rabbits, but the parasite was found to be non-pathogenic to these animals.

It was demonstrated that this trypanosome multiplies in the spleen, where the stages of division are confined to the capillaries. Multiplication follows the inoculation of metacyclic trypanosomes from infected fleas or blood forms. It proceeds by division of the nucleus and kinetoplast into four, followed by fission of the cytoplasm, giving rise to four small daughter individuals. These are transformed into trypanosome forms, which are shed into the peripheral blood, where they change into the typical adult trypanosomes.

The development in the intermediate host takes place in the gut of the rabbit flea, Spilopsyllus cuniculi, with the production of metacyclic trypanosomes in the hind-gut (posterior station).

The nomenclature and synonymy of the rabbit trypanosome are discussed, and it is concluded that its valid name is Trypanosoma nabiasi Railliet, 1895.

The results of the examination of 543 faecal specimens by the Merthiolate Iodine Formaldehyde Concentration (M.I.F.C.) technique, Willis's salt flotation method and by direct saline smear are given.

The appearances of helminth ova and protozoan parasites in M.I.F.C. preparation are described.

The M.I.F.C. method showed a much greater efficiency for the detection of helminth ova over the other two methods. It did not prove as satisfactory for the detection of protozoan parasites. Effective concentration of trophozoite forms was not observed. The possible reasons for this are discussed.

It is proposed to adopt this method in combination with the direct saline smear for routine use in this laboratory.

Species of the genus Pennella are of interest because they parasitize widely different hosts such as cetacea, flying fish, pipe fishes, sword fishes, etc. In 1917 Wilson listed fourteen valid species and nine more have been added since. Of these P. exocoeti (Holten) and P. blainvilli (Le Sueur) have been recorded as parasites of flying fishes, the former probably in Exocoetus speculiger from which Leigh-Sharpe (1928) and Deboutteville & Nunes-Ruivote (1954) recorded the species, while the latter was found on E. volitans. The present paper deals with four parasites collected from four different species of flying fishes of Madras. The types will be deposited in the Indian museum, Calcutta.

Although the biological control of medically important snails has been suggested from time to time during the past quarter of a century (Nagano, 1927; Bequaert, 1928; Mozely, 1939, 1951; McMullen, 1952), the subject has, as yet, received but little serious consideration. Upon the initiation of our studies (Chernin, Michelson & Augustine, 1956a, b) the literature was searched for references to predators, parasites and diseases of molluscs which might furnish leads for experimental investigation.

1. A fork-tailed cercaria Cercaria diplostomi phoxini (Faust) has been found to develop in sporocysts in 3·9 % of Lymnaea pereger var. ovata (Drapanaud) in Fron Goch Pool near Aberystwyth.

2. The cercaria is described in detail. The arrangement of spines on the body is characteristic and there is a double row of seventy-two spines on the ventral sucker. The flame cell formula is given.

3. The cercaria is compared with seven closely related types.

4. Infestation experiments show that Cercaria diplostomi phoxini develops into Diplostomulum phoxini in the brain of the minnow.

5. The early stage of infestation of the brain of the minnow is described and compared with an infestation of long standing.

The ability of certain species of trypanosomes (T. lewisi and T. equiperdum) to ingest previously stained oil drops which occurred simultaneously in the blood has been observed.

Tryparsamide incorporated in dyed (Sudan IV) cod-liver oil.when administered orally, was found to be effective against T. equiperdum infections in mice.

In a collection of parasitic mites from Palestine sent by Prof. O. Theodor, Hebrew University, Jerusalem, the author found several larval mites which prove to be new species, one in the genus Euschöngastia the other two in the genus Trombicula. These are described and figured in the present paper along with a new species of the genus Blankaartia taken on a bird in Uganda and sent for identification by G. H. E. Hopkins, O.B.E. (formerly Senior Medical Entomologist, Kampala). The author wishes to acknowledge his thanks to the above donors for having given him the opportunity to examine these specimens.

A score of these large amphistomes were found in the collection made by Dr P. L. LeRoux, to whom we wish to express our gratitude for the privilege of examining them, and to Professor J. J. C. Buckley for his interest in the work. The characteristically large posterior sucker and its muscular structure places this amphistome in Nasmark's Gigantocotyle.

1. The male of Rhipicephalus humeralis is redescribed and the female and immature stages are described for the first time. The synonymy of the species is discussed and the various stages are compared with those of R. pulchellus.

2. Details of the life cycle under laboratory conditions are given.

3. The host list and distribution of the species are given.

1. P. tularensis may be abundant in the midgut lumen, the epithelial cells of the anterior third of the midgut, and the haemolymph of the louse. Multiplication is extracellular in the lumen and the haemolymph and intracytoplasmic in the gut cells.

2. The multiplication of the tularemia organisms in the midgut epithelium eventually leads to the disruption of these cells and the break-through of the organisms into the body cavity. The growth of these organisms in the haemocoele results in the death of the louse in 4–7 days.

3. Lice vary greatly in their susceptibility to infection. Some lice show complete resistance to infection; others are capable of retaining the infection essentially for their normal life span, i.e. 35 days; still others apparently succumb to a rapid increase of the organisms in a relatively brief time after infection.

4. The behaviour of P. tularensis within the louse presents interesting similarities to infection of lice with the rickettsiae pathogenic to humans.

1. A series of experiments is described in which the transmission of cattle lung-worm infection has been investigated in relation to four different pasture conditions—long grass, short grass produced by gangmowing, grazing by sheep and grazing by resistant cattle.

2. The methods of study of value in this type of field investigation are discussed. It is suggested that the results can be usefully expressed as a series of coefficients which summarize the factors involved in the process of transmission. The methods of calculation of these coefficients are described.

Copepods belonging to the genus Lamippe live in the gastrovascular cavity of several alcyonarian genera. Eighteen species of these copepods are known (Zulueta, 1911), nineteen if the variety L. rubra decolor Zulueta 1908 is raised to species rank as suggested by Heegaard (1949). Each species is highly preferential in its choice of a host. Only one species is known to parasitize more than a single species of coelenterate, namely L. rubicunda (Olsson, 1869) which lives in two species of Alcyonium.

1. Psilochasmus agilis Travassos, 1921, is regarded as synonym to P. oxyurus Lühe, 1909.

2. P. indicus sp.n. has been described.

3. An amended specific diagnosis of Psilochasmus oxyurus has been given.

4. Ruddy Shelduck or Brahminy duck, Tadorna ferruginea (= Casarca rutila) is recorded as a new host of the genus.

Lavoipierre & Griffiths (1951) described the female, and Lavoipierre (1953) described the male, of Knemidokoptes pilae found on a budgerigar. Later, Oldham & Beresford (1954) and Evans & Browning (1955), respectively, added Psittacula nipalensis and Upupa epops to the host-list of this species. The present author (1956) has also mentioned the occurrence of Knemidokoptes pilae on a budgerigar and a parrakeet, Palaeornis torquatus, and an unknown species of the genus Ara may now be added to the list.

Only 10 species of Nycteribiidae have been recorded previously from the Ethiopian Region and 3 further species from Madagascar. The writer recently described the new genus Dipseliopoda with three species, a new species of Eucampsipoda from Africa and another from Madagascar, (Theodor, 1955), 3 new species of Basilia and a new species of Tripselia from Africa (Theodor, 1956).

Some time ago Mr E. Wilson, of the Marine Laboratory, Aberdeen, brought to notice the abnormal appearance of the cranial cartilage in a plaice (Pleuronectes platessa L.) which had been tagged (in St Andrews Bay) and subsequently recaptured (24 miles south-south-east of Arbroath). The fish was a 44·5 cm. long female, 6 years old, with mature ovary and in good condition generally. The cartilage, exposed by the opening of the cranium to remove the otoliths, seemed hypertrophied and full of whitish splotches giving it a mottled appearance. These ‘splotches’ were formed by irregular, vein-like branching canals, in many places along their length swelling into cyst-like, subspherical cavities up to 3 mm. in diameter. They were filled by a mass of soft substance which was found to be an accumulation of Cnidosporidian spores. Small granules of the substance were also found inside the otic capsules. It is possible, however, that these granules were displaced into the capsules during the opening of the cranium.

The external structure of the capitulum of all stages of Dermacentor parumapertus is described in detail. The capitulum is divisible into an extra-basis and basis regions. The former consists of a dorsally grooved hypostome or food channel overlapped by a labral membrane, along its whole length. The salivary channel lies above the labral membrane, being bordered laterally by the meso-ventral margins of the outer cheliceral sheaths. Within the basis a vertical wall separates the base of the palpal cavity from the rest of the basis. This wall is produced backwards to form a wing or ala on either side of the pharynx and to it are attached dilator and constrictor muscles. Opening of the fore-part of the pharynx, i.e. where it is in the form of a V-shaped depression overlapped by a wedge, is effected by ventral and ventro-lateral dilator muscles, and closure by the elasticity of the pharyngeal walls.

The pharynx, oesophagus and salivary glands are described.

1. This paper reviews the morphology, distribution and hosts of I. schillingsi Neumann, 1901.

2. Two new species, I. rageaui from the Cameroons, and I. lemuris from Madagascar are described and figured. The latter shows obvious African affinities and is but slightly different from its African relative.

3. I. schillingsi is, with the exception of Lophiomys ibeanus (crested rat), known only from Colobus monkeys, I. rageaui from monkeys of the Cercopithecus group and I. lemuris from Lemur rufifrons.