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.

Opistholebes diodontis n.sp. is described from the intestine of the porcupine fish, Diodon hystrix, and development from the metacercaria to the adult is outlined. In that process, the ventral sucker shifts from near the mid-level to the posterior end of the body and other rearrangements occur as a result of differential growth. Hence in the Opistholebetidae and probably the Gyliauchenidae and Cephalo-poridae as well, the amphistome plan is considered to be secondary in phylogeny. None of those families belongs in the Paramphistomoidea. Instead, each is believed to be a distinct family of aberrant trematodes derived from a separate line of more generalized distomes. Representing one such line of descent are the Opistholebetidae and Opecoelidae which are more closely related to each other than either is to any other group. Hence a superfamily, Opecoeloidea, is proposed to include the two families and set them apart as a natural group distinct from the remainder of the allocreadioid complex which is discussed. The genus Pachycreadium is transferred to the Opistholebetidae, family diagnoses are revised, and a key to the species of Opistholebes is given.

This contribution is intended to be the last of this series. As one who may claim to have revived interest in these crustaceans from this region since the days of Bassett-Smith just prior to the beginning of the century, I find it particularly gratifying that several Indian zoologists are now steadily engaged in adding to our knowledge of these forms. Altogether some forty-three genera containing about 120 species have now been recorded from the Indian Ocean. This must form only a small fraction of the total number of forms that actually occur on the wide variety of hosts inhabiting this region.

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.

The alimentary tract of female Culicoides nubeculosus is simple. There is much similarity between it and that of other nematoceran and brachyceran bloodsucking flies.

Among the interesting features observed are the following:

1. The mid-gut is composed of two portions, a tubular anterior segment and a dilated stomach, which show structural differences.

2. The peritrophic membrane, which is absent in the unfed female, forms around the ingested blood. Its substance is secreted by the epithelium of the stomach.

3. A simple rectal valve guards the opening of the small intestine into the rectum.

4. The Malpighian tubules are two in number, and they give attachment to muscular branches from different sources.

5. There are six accessory glands arranged in a rosette around the mouth of each salivary gland proper. Some of them may sometimes function as reservoirs for the secretion of the salivary glands proper.

In one specimen, tumours at the base of the stomach and abnormal features in the Malpighian tubules were observed.

The microsporidian described in this paper is parasitic in the fat-body of Gono-cephalum arenarium (Order Coleoptera; Family Tenebrionidae), a root-feeding beetle which is usually found sheltering under stones or fallen leaves and in lawns in South Africa. During the present investigation only adult insects were available for study as the earlier phases of the life history doubtless occur beneath the surface of the soil.

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.

1. An account is given of the history, synonymy and host-range of Toxocara cati.

2. Eggs of T. cati were fed to various animals, and the second-stage larvae were found in the tissues of earthworms, cockroaches, chickens, mice, dogs, lambs and cats.

3. Cats were successfully infected by feeding eggs of T. cati and by feeding mice harbouring larvae in the tissues.

4. In egg-infected cats the larvae were found in the liver, lungs, muscles and tracheal washings as well as in the digestive tract, indicating that they migrate through the tissues.

5. In mice the larvae were found in the liver, lungs and muscles, but did not reach the alimentary tract. Changes occurred in the mouth region of the larvae in mouse tissues between 8 and 11 days after infection, but no actual moult was observed. No significant growth of the larvae was observed in mouse tissues.

6. In mouse-infected cats the larvae were mostly confined to the wall and contents of the digestive tract.

7. It appeared that the second moult occurred in the stomach wall of egg-infected cats at 3–10 days after infection; moulting larvae measuring 0·353–0·423 mm. in length; in a mouse-infected cat moulting larvae (length 0·459–0·765 mm.) were observed at 6 days after infection.

8. In both egg- and mouse-infected cats the third-stage larvae grew in the stomach wall and moulted for the third time at a length of 0·9–1·2 mm. This occurred at about 10 days in mouse-infected cats and at about 19 days in egg-infected cats.

9. The smallest fourth-stage larvae were found in the stomach contents whence they passed into the intestine. Probably they are at first attached to the wall and later become free in the intestinal contents.

10. The fourth-stage larvae have lips resembling the adult; sexual differentiation occurs during this stage, being first evident at 1·5 mm.

11. The fourth moult occurs in the intestine at a length of approximately 4·5–5·5 mm.

12. In the adult stage the lateral alae gradually disappear and the cervical alae reach the adult form at a length of approximately 45 mm. The smallest female observed containing eggs in the vagina measured 55 mm. in length. Eggs were first observed in the faeces at 56 days after infection by eggs.

13. The evidence from experimental and natural infection indicated that infection of cats with T. cati always takes place after birth.

14. No larvae were found in the alimentary tract of dogs following experimental infection either with eggs or with infected mice.

15. The relationship of the life history of T. cati to that of other ascaridid species, to the feeding habits of the definitive hosts, and in relation to the occurrence of human infection with this parasite is discussed.

1. Suspensions made from infected caecal material, derived from chickens which had been artificially infected with Histomonas meleagridis by the administration of embryonated Heterakis ova, can be used to transmit the organisms to other chickens when administered per os.

2. Infections with histomonad suspensions can only be obtained in chickens that have been starved, or in chickens that are feeding but have received an alkali mixture immediately before the suspension is administered. The highest incidence of infections is obtained by administering suspensions to starved chickens that have received 1 g. alkali mixture beforehand.

3. Successful infection appears to depend upon the pH of the gizzard and, possibly, of the upper intestine. The incidence of lesions produced by feeding suspension is increased as the contents of the gizzard become alkaline. It is also suggested that the consistency of the food may play a part, as coarse food, along with the infective material, is retained in the gizzard until it is completely ground up and mixed with the gastric juice.

4. In one series of passages the suspension became attenuated after fourteen passages through chickens. In other cases suspensions became attenuated after only six passages through chickens.

5. The courses of infections produced by histomonad suspensions and Heterakis ova are compared.

6. The advantages of the method of using histomonad suspensions are discussed in their relation to the screening of chemotherapeutical agents.

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.

While human schistosomiasis is hardly a problem in India, schistosomiasis in domestic animals is a problem of considerable importance. Blood-flukes infect almost all the species of Indian domestic animals, and often seriously undermine their health and usefulness. Seven species of schistosomes are known to occur in Indian mammals, viz. Schistosoma indicum Montgomery (1906a), S. spindalis Montgomery (1906b), S. incognitum Chandler (1926), S. nasalis Rao (1933), Bivitellobilharzia nairi (Mudaliar & Ramanujachari, 1945) Dutt & Srivastava (1955), Orientobilharzia dattai (Dutt & Srivastava, 1952) Dutt & Srivastava (1955), and Orientobilharzia bomfordi (Montgomery, 1906b) Dutt & Srivastava (1955). The reported occurrence of Schistosoma bovis (Sonsino, 1876) Blanchard (1895) in India needs confirmation.

1. Of thirty-four Apodemus sylvaticus examined from in and near Exeter, thirteen were infested with varying numbers of the dicrocoeliid trematode, Corrigia vitta.

2. The worms live in the interlobary canals of the pancreas, sometimes singly, but up to eight have been found in a single mouse.

3. The dimensions of the more important organs are stated and compared with the measurements provided by other authors.

4. The taxonomic status of the species is briefly considered.

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 egg-shell in many trematodes and pseudophyllidean cestodes is a quinone-tanned protein; and histochemical methods for polyphenol oxidase or for phenols may be used to demonstrate regions producing or containing shell material (i.e. the vitellaria, its ducts and the uterus) in whole mount preparations.

2. Specimens so treated may be further stained by routine whole mount methods. Gower's carmine is particularly recommended.

3. 70% alcohol was found to be the best general fixative for these methods.

4. These histochemical methods—with certain modifications—may also be used for demonstrating the egg-shell producing regions in sections.

5. Because of their affinity for basic proteins, bromo-phenol-blue and malachite green are suitable for staining these regions in sections. These stains are unsuitable for whole mounts.

6. There is some evidence to suggest that all trematodes and pseudophyllidean cestodes do not form and harden their egg-shell by quinone tanning; consequently, some forms may give negative or unsatisfactory results with these methods.

1. Cysts, formed in a strain of E. invadens growing with a mixed bacterial flora, were sterilized of all but one species of bacterium (organism x), by treatment with chemicals. Strains of E. invadens derived from these cysts were prepared, growing with organism x and either Bact. coli or B. megatherium.

2. A monobacterial strain of E. invadens, growing with Bact. coli alone, was obtained by maintaining a dibacterial strain, growing with organism x and Bact. coli, for 72 days in medium containing gentian violet.

3. A monobacterial strain of E. invadens, growing with Staph. albus, was prepared from cysts, produced in the monobacterial strain of E. invadens + Bact. coli, and sterilized by treatment with chemicals.

4. An axenic strain of E. invadens was prepared by maintaining the monobacterial strain of E. invadens + Staph. albus, in saline-liver medium containing antibiotics. This axenic strain has now been maintained for over 14 months in saline containing untreated, sterile liver, but no antibiotics.

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.