The adults of Rhipicephalus pravus were first described very briefly by Dönitz, in 1910, from specimens collected from buffalo, giraffe and various antelopes on the Masai Steppe in Tanganyika. He did not designate any specific specimens as types. He compared the species with R. oculatus, but stated that the difference in the structure of the eyes of the two forms, which he described in detail, was so marked that he considered it to be specific. He also commented on the fact that the males of R. pravus are often strikingly narrow anteriorly, but added that this is not a decisive character. Zumpt (1942) redescribed the adults in detail from material collected in the Tanganyika highlands (Arusha, Kilimatinde, Kondoa-Irangi, Mkalama, Morogoro and Mpwapwa), in Kenya (Mt. Nyro and Mt. Loroghi) and in Abyssinia (Diredawa). Theiler & Robinson (1953) gave descriptions of adults collected at Fairmount, Edenburg, Orange Free State and of nymphae and larvae bred from them in the laboratory. They also discussed the biology, distribution and synonymy of the species. The following descriptions of the adults, nymph and larva are based on laboratory-bred specimens, the progeny of a female collected at Kima, approximately 90 miles south-east of Nairobi.

1. The spiracular plate is made up of three layers, (a) the outermost non-porose plate, which varies in thickness, being thicker where the (b) intermediate layer of pedicels fuses towards the outside, and thinner over the goblets. The innermost layer (c) is of even thickness, and corrugated.

2. The ostium is bounded by the columella dorsally and by the lower lip ven-trally, both of which are continuous with the thickened antero-ventrally placed macula.

3. The ostium opens into a subostial space which in turn passes into the atrium. The ventral and ventro-lateral walls are thrown into two folds about midway along, and then anteriorly and posteriorly merge to form a single lobe. The musculature associated with the atrium is described.

4. On morphological grounds it appears that the ostium is incapable of opening and closing, and it is suggested that only opening muscles—the dorsal and ventral atrial muscles—are present.

5. The distribution of the main tracheal trunks is described.

6. Hailer's organ in the female of I. hexagonus consists of a trough and a capsule; the former bears six hairs divisible into types I–IV and the latter contains seven tapering sensillae. This pattern is applicable to both the male and the nymph: in the larva one type III sensilla is missing from the trough and only 4 sensory hairs are present in the capsule.

7. A description of Haller's organ in the British Ixodes species is given, and it is shown to be of systematic value.

8. The status of species possessing ‘trough-nosed’ capsules is discussed, and the validity of giving such species generic rank does not appear to be justified. As far as the material investigated is concerned there seems little difference in the sexes, with the exception of I. muris and I. loricatus, nor has any correlation been established between the structure of the organ and host specificity.

1. A survey of 227 rooks (Corvus frugilegus frugilegus L.) and seventy jackdaws (C. monedula spermologus Vieill.) was conducted in Hertfordshire. The birds were examined by means of cultures of their peripheral blood, or (in the case of eleven rooks and one jackdaw only) bone-marrow, on N.N.N. medium. Twenty-seven rooks (11·9%) and six jackdaws (8·6%) were found to be infected.

Some of the rooks were examined at a time of year when the trypanosomes are not present in the peripheral circulation; other rooks were examined in the first year of their life before adults of Ornithomyia avicularia (the vector of this parasite) were present. Ignoring birds of these two groups, twenty-six out of seventy-eight (33·3 %) adult rooks were found to be infected. This value probably approximates to the natural infection rate among adult rooks (and perhaps jackdaws).

2. The trypanosome in question is a large spindle-shaped form, measuring an average of 48·2µ in length (excluding flagellum) and 5·5µ in width. There is a tapering aflagellar region extending 14·1µ (on the average) beyond the kineto-plast. This trypanosome is assigned to the species T. avium Danilewsky, 1885.

1. It is shown that Ornithomyia avicularia L. (Diptera, Hippoboscidae) is a vector of Trypanosoma avium in this country.

2. The metacyclic trypanosomes develop in the insect's hind-gut, and infect birds by penetrating the membranes of buccal cavity and/or oesophagus and crop.

3. The opportunity for infection to take place occurs when birds ingest infected insects.

4. The significance of this finding in connexion with other reports of (a) vectors of avian trypanosomes, and (b) trypanosomes transmitted by hippoboscids, is discussed.

5. Attempts to obtain development of T. avium in a few nymphs of Rhodnius prolixus and one adult Culex molestus, failed. Mites from an infected bird were examined for the presence of flagellates, with negative results.

1. The life cycle of Trypanosoma avium in both its hosts is described.

2. In the vector (Ornithomyia avicularia) it undergoes a cyclical development in the alimentary canal. Multiplication occurs while the flagellate is in the crithi-dial stage, and, finally, pyriform haptomonad crithidia appear in the insect's hind-gut: these change into the infective metacyclic trypanosomes.

3. After penetrating the mucous membranes of the bird (following its ingestion of the louse-fly), the metacyclic trypanosomes probably invade the lymph system, and there develop (by growth alone) into the large forms seen in the bird's blood some 18–24 hr. later.

4. The trypanosomes persist in their natural hosts (but not in canaries) throughout the winter, more-or-less restricted to the bone-marrow. In the spring they reappear in the peripheral blood.

Some species of Nycteribiidae have been recorded from widely different faunistic regions. Thus, Eucampsipoda hyrtlii has been recorded from Africa, Ceylon, Burma and Sumatra. Other species have been recorded from Europe and China or from Europe and South Africa. Re-examination of the material has proved in most cases that the species were wrongly identified and no species has been found so far to exist both in Europe and in East Asia. There remained finally two species which have been recorded from the Ethiopian and the Oriental region, Tripselia blainvillii and Basilia bathybothyra. Material of these two species from as many localities as possible was therefore brought together, in order to determine whether this wide distribution does in fact occur or whether, in these cases as well, there existed different forms, species or subspecies, with a narrower range of distribution.

It is concluded that E. sibiricensis is the etiologic agent of alveolar hydatid disease in man. The cestode has a wide distribution in Eurasia, and St Lawrence Island apparently represents the north-easternmost extent of its range. The study of the cestode in Europe has been complicated by the co-existence of E. granulosus, which does not occur on St Lawrence Island. Microtine rodents, particularly Microtus spp. and Clethrionomys rutilus, are the natural intermediate hosts of this cestode, although other species of mammals, including man, are parasitized with varying degrees of success on the part of the larval cestode.

1. Camallanus anabantis is recorded from Ceylon in Anabas testudineus, Ophicephalus punctatus, Puntius filamentosus and Rasbora daniconius. P. filamentosus, R. daniconius and O. punctatus are new hosts for this species.

2. Camallanus sweeti is recorded from Ceylon in Anabas testudineus, Ophicephalus punctatus, Ophicephalus striatus and Rasbora daniconius. One third stage larva was observed in each of O. punctatus and Clarias batrachus. O. punctatus, O. striatus and R. daniconius are new hosts for this species.

3. Procamallanus planoratus is recorded in Clarias batrachus, Ophicephalus punctatus and Ophicephalus striatus from Ceylon. O. punctatus and O. striatus are new hosts for this species.

4. Variations in the anatomy of the posterior ends of the three species are mentioned.

5. No Camallanidae were obtained from Macropodus cupanus, Puntius chola, P. dorsalis, P. vittatus, Panchax panchax, Nemacheilus botia botia, Etroplus macu-latus and Etroplus suratensis.

6. Reasons are given for suggesting direct infection of the host from the first intermediate host, although a ‘carrier host’ may exist.

The material used in the present study was part of a collection of parasitic worms, from whales in the Ross Sea, given to the writer by Mr W. Ross Cockrill, F.R.C.V.S. A general account of this collection has already been published (Rees, 1953).

1. The life cycle of Gigantobilharzia huronensis Najim, 1950, was determined experimentally. The snail, Physa gyrina (Say), served as the intermediate host. The natural definitive hosts were goldfinches (Spinus tristis tristis) and the cardinals (Richmondena cardinalis). Chicks and canaries served as susceptible hosts in the laboratory

2. The shortest time recorded for the hatching of eggs in water is about 20 min. Cercariae were liberated from the snail as early as 24 days after exposure. Eggs were found in the faeces of the definitive host 31 days after the first exposure to the cercariae.

3. Adult worms are elongate and filiform. Females are longer than males, and in both sexes the oral and ventral suckers are absent. The cuticle has no spines. A short gynaecophoric canal is present. Up to 300 testes are present in the male and the cirrus is spiny. Laurer's canal is present and vitelline follicles fill most of the body of the female. Eggs are spherical to very broadly ovoid in shape and averaged 93µ in length by 88µ in width. The uterus contains from one to several eggs at a time, and the genital pore is located shortly posterior to the mouth opening.

4. The miracidium has a peculiar wide gap between the second and third rows of epidermal plates. The body covering consists of twenty-two epidermal plates arranged in four rows of 6:9:4:3. The mother sporocyst has an elongate, sac-like body. A birth pore is present in the mature mother sporocysts. The daughter sporocyst also has an elongate body, but the anterior end is covered with spines. A birth pore is present in the mature daughter sporocysts.

5. The cercaria is an apharyngeal, furcocercous, brevifurcate, distome with pigmented eyespots; the body averaging 240µ in length by 72·5µ in width; the tail stem averaging 268·5µ in length by 30µ, in width; the furca averaging 146·8µ in length by 15µ in width. The furcae have fin folds. The body and tail are covered with spines. There are five pairs of penetration glands and an oral gland. The excretory system is usually 2[(2) + (2+1)]. The cercaria attaches to the surface film of the water with the body parallel to it and the tail hanging downward at different angles. The cercaria is a dermatitis producer in human skin.

1. The life cycle of Austrobilharzia terrigalensis Johnston, 1917 is described. The larval stages occur in Pyrazus australis, a common mollusc on sand flats of estuaries and coastal lagoons in New South Wales.

2. Austrobilharzia terrigalensis was originally described from the seagull, Larus novae-hollandiae. Experimental infections have been successful in young gulls of this species and in the budgerigar Melopsittacus undulatus and the pigeon Columba livia.

3. Under experimental conditions the cercariae will cause dermatitis, and cases of dermatitis resembling cercarial dermatitis have been reported after bathing in Narrabeen Lagoon, where about 4 % of Pyrazus australis carry forktail cercariae.

4. The cercaria was described previously (Bearup, 1955) as Cercaria variglandis subspecies pyrazi, new subspecies. Now that the adult form has been identified as a previously described species the subspecific name pyrazi lapses.

Epidemics in English crayfish, Astacus pallipes, were found to be due to micro-sporidia and yeasts similar to, if not identical with, those causing diseases in another Crustacean, namely, Gammarus pulex, in many parts of England.