Records are presented of 11 species of parasitic helminths recovered from 37 American avocets. Birds were collected in Kansas and Colorado from April 1973 to August 1974. Parasites found included 3 trematodes, 2 nematodes, 1 acanthocephalan and 5 cestodes, 4 of which are new species. Hymenolepis cervotestis sp.n. (Hymenolepididae) is described from the small intestine of 7 avocets. It exhibits extreme protandry with the testes appearing before external segmentation is evident. Sobolevicanthus coloradensis sp.n. (Hymenolepididae) is described from the small intestine of 4 avocets. This species is found to have its scolex embedded in the intest-tinal mucosa of its host. Diorchis recurvirostrae sp.n. (Hymenolepididae) is described from specimens recovered from the small intestine of 5 avocets. Diplophallus coili sp.n. (Acoleidae) is described from the small intestine of all 37 avocets. The family Diploposthidae is suppressed and the family Acoleidae is emended to include the 4 genera previously placed in Diploposthidae. A key to the genera of Acoleidae is presented.

In this paper the history is given of the maintenance away from man of certain strains of T. rhodesiense originally isolated from man in Tanganyika Territory.

Since writing our recent review (Markham, Smith & Lea, 1942) on the sizes of viruses and the methods employed in their estimation, another virus has been added to the list of those concerning which we have concordant information by so many different methods that conclusions as to the size and shape and degree of hydration can be drawn with some confidence. This is the Shope rabbit papilloma virus, electron micrographs of which have been published by Sharp, Taylor, Beard & Beard (1942), and for which data on diffusion, sedimentation, density and viscosity have been published by Neurath, Cooper, Sharp, Taylor, Beard & Beard (1941). These data may be worked up by the formulae given in our review, and this note will serve to illustrate the convenience of our formulae for such purposes.

Nine out of thirty-three specimens of the common shrew Sorex araneus, caught at Rosta in north Norway in August 1953, were found to be infected with Grahamella (Rickettsiales). Nine specimens of Clethrionomys rutilus, nine of Microtus oeconomus ratticeps and one of M. agrestis, caught at the same time and place, were found to be free of Grahamella. No other blood parasites were found in any of the animals examined.

Records by other authors of Grahamella in a variety of hosts are reviewed. The parasite is known to occur in mammalian hosts only: identifications of it in non-mammalian hosts can be discarded. Host specificity, tacitly assumed by most authors, is not proven, and therefore most of the specific names bestowed on Grahamella in different hosts are of doubtful validity. The morphology of the parasite varies little from host to host; and there is little evidence to show that its pathogenic effect on any host is serious. Grahamella has been cultured by a few authors: variations in characters of these cultures may be more reliable criteria for recognition of different species of Grahamella.

These small mammals were collected while I was a member of the University of Edinburgh Expedition to Arctic Norway, 1953. I wish to thank all who were concerned, in particular Dr D. M. Steven, with whom I did the trapping. The rest of the work was done during the tenure of a Research Studentship awarded by the Agricultural Research Council. I also wish to thank Dr P. Tate for his advice and his criticisms of the manuscript.

Laboratory rodents vaccinated with highly irradiated cercariae of Schistosoma mansoni develop significant levels of specific acquired resistance yet effect challenge elimination in different organs. Mice and guinea-pigs are at opposite ends of the spectrum in this respect since, in our hands, vaccinated mice kill challenge parasites in the skin whereas vaccinated guinea-pigs kill challenge parasites predominantly in the liver. To determine whether this phenomenon is host-dependent (site) or parasite-dependent (stage), we have transferred worms harvested from mice or guinea-pigs into vaccinated recipient guinea-pigs. The results show that mouse-derived 5-day lung worms and 9-day liver worms that are essentially refractory to vaccine resistance in mice are indeed susceptible to vaccine resistance in guinea-pigs. Identical levels of susceptibility were recorded for lung-stage larvae introduced via the foot vein so as to experience lung and liver mechanisms, or via the mesenteric vein to bypass the lung, thereby confirming that vaccine resistance in guinea-pigs operates in the liver. Mouse worms and guinea-pig worms exhibited equivalent levels of susceptibility at all stages of development. Thirteen-day-old larvae from either donor species were on the border-line of vulnerability, while 20-day-old worms were totally refractory to vaccine immunity in guinea-pigs. These data show that vaccine immunity in different rodent species is a site-dependent, rather than a stage-dependent phenomenon. There is, however, an upper age limit of schistosome vulnerability which is common to worms harvested from different donor species.

1. The development of exo-erythrocytic parasites of Plasmodium gallinaceum is more rapid and intense in chicks inoculated with blood from birds heavily infected with exo-erythrocytic parasites than in those inoculated with blood from birds in which no exo-erythrocytic parasites can be found.

2. If parasitized blood from a bird heavily infected with exo-erythrocytic parasites is inoculated intravenously into a normal bird and withdrawn 24 hr. later, it produces infections in normal birds characterized by a slow development of exo-erythrocytic parasites.

3. The proportion of birds which survived after inoculation with P. gallinaceum and daily treatment with suppressive doses of quinine, mepacrine or pamaquin, was greater when the inoculum was derived from donors in which no exo-erythrocytic parasites could be found (48%) than in those inoculated with blood from donors in which exo-erythrocytic parasites 'were numerous (15). No birds inoculated with parasitized blood from donors heavily infected with exo-erythrocytic parasites were sterilized of their infections by the action of the drugs, whereas in eleven out of sixty-six of the birds inoculated with parasitized blood from birds in which no exo-erythrocytic parasites could be found the infections were eradicated by the drugs.

4. Blood-inoculated infections of P. gallinaceum may in some cases be eradicated by short courses of treatment with mepacrine, quinine or pamaquin.

5. Whereas blood-inoculated infections of P. gallinaceum derived from donors in which no exo-erythrocytic parasites could be found were sometimes eradicated by prophylactic treatment with quinine, mepacrine or pamaquin, it was not possible to eradicate the infections by curative treatment with similar doses of these drugs.

6. The difference in type of infection produced by parasitized blood from birds in which no exo-erythrocytic parasites could be found at the time of withdrawal of the blood and those in which exo-erythrocytic parasites were plentiful appears to be due to the presence of exo-erythrocytic parasites in the circulating blood of the latter type of donor.

7. Sterilization by the action of quinine, mepa-crine or pamaquin of blood-inoculated infections from donors in which no exo-erythrocytic forms could be found, appears to depend upon whether the erythrocytic parasites are killed before they can become converted into exo-erythrocytic forms.

8. No evidence has been obtained of the intensification of development of exo-erythrocytic parasites by the suppression of erythrocytic parasites with drugs.

After treatment with arsenophenylglycin the number of trypanosomes in an infected animal immediately begins to decrease, and the parasites disappear from the peripheral circulation 6—7 hours after the time of injection, the short stumpy forms being the last to degenerate.

One of the first changes noticed in the trypanosomes after treatment is the rounding up of their posterior extremities caused by the retraction of the protoplasm behind the kineto-nucleus. Meanwhile the tropho-nucleus becomes filled with granules of volutinose, which are extruded into the cytoplasm and pass along the axial filament towards the anterior extremity of the body. In dividing forms the granules form two longitudinal rows, being distributed along the two axial filaments. Finally, the granules lose their regular arrangement and become scattered throughout the cytoplasm, being more abundant, however, at the anterior end.

The kineto-vacuole, when present, enlarges considerably and may become filled with chromatic substance derived from the kineto-nucleus.

The axial filament begins to degenerate soon after treatment, often breaking up into a row of granules. Occasionally, however, chromatic substance from the kineto-nucleus passes along the axial filament, and it then appears as a thick black band extending along the middle of the cell eventually to the anterior extremity. Subsequently it breaks up into granules which dissolve in the cytoplasm of the cell.

Chromatic bodies are given off from the kineto-nucleus both before and after treatment and do not seem to be a characteristic feature of degeneration.

Sometimes the tropho-nucleus completely disappears before the cytoplasm breaks up into fragments, but at other times it preserves its form long after all other parts of the trypanosome, with the exception of the flagellum, have disappeared. These free nuclei resemble the “latent bodies” described by Salvin-Moore and Breinl, but as they, along with the fragments of cytoplasm, granules etc., are ingested by the leucocytes, it seems possible that they are merely one of the results of degeneration and not part of the life-cycle of this parasite.

These investigations have been carried on partly with the aid of a grant from the Tropical Diseases Research Fund (Colonial Office).

1. The larva and nymph of Rhipicephalus pulchellus are described for the first time and comments are made on the degree of variation in structure seen amongst adults of a single generation.

2. Information on various aspects of the biology of this tick and on classification is given.

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.

A new cestode of unusual anatomical characteristics was collected from a group of Gerbillus pyramidum caught in August 1953, in the vicinity of Tel Aviv. It appears to be a new species of a new genus for which the name of Rajotaenia gerbilli n.g. n.sp. is proposed. Thanks are due to Mr M. Costa for collecting the infected rodents.

Males of Nematodirus battus have a body wall composed of a longitudinally ridged cuticle made up of 8 layers, a hypodermis and a layer of longitudinal muscle cells which are divided into 4 sectors by the hypodermal cords. There is a characteristic cephalic inflation of the cuticle in both sexes. The structure of the body wall in the anterior half of the female is similar to that of the male. In the posterior half of the female the cuticle is not ridged and has 7 layers; the longitudinal muscles are reduced in number and the lateral hypodermal cords increasingly extend dorsally and ventrally along the length of the posterior part of the nematode and come to occupy most of the lateral sectors of the body. The possible significance of these modifications in the structure of the female nematode are discussed.

In mice infected with the intestinal flagellates Giardia muris or Spironucleus muris, together with the blood parasites Babesia microti or Plasmodium yoelii, there is a temporary decrease of flagellate cyst output coincident with the peak of the blood parasite infections, followed by a rapid return to normal levels. This decrease in cyst output is correlated with decreased numbers of trophozoites in the small intestine. The effect on S. muris is more marked than that on G. muris. Neither blood parasites has any effect on the total duration of the flagellate infection and the flagellates do not affect the blood parasites. In mice infected with G. muris or S. muris and P. berghei there is also a decrease in cyst output but this is less apparent than in infections with B. microti or P. yoelii because of the fatal nature of the P. berghei infection. It is suggested that the decrease in cyst output is probably due to changes in the contents of the small intestine or to non-specific immunological factors rather than to specific immunological changes.

The mature egg and the acanthor of Moniliformis dubius have been redescribed with special emphasis on the features relevant to the locomotion of this larval acanthocephalan. The movements of acanthors have been analysed by the use of frame by frame study of filmed records of motile acanthors. Acanthors appear to use the same mode of locomotion for hatching, locomotion within the gut of the intermediate host and penetration of the host's gut wall. Movement is produced by a set of spiralled, longitudinal muscles in the body wall of the hind body and two rostellar retractor muscles. This musculature acts both directly on the body wall and indirectly by hydraulic effects via the hydrostatic skeleton of pseudocoelomic fluid. The spiny evertable rostellum and the backward facing spines of the hind body are the means whereby shape changes of the acanthor interact with the immediate environment to produce effective progression.

I should like to thank Professor D. Arthur for the provision of laboratory facilities, Dr D. W. T. Crompton for the initial gift of eggs of M. dubius and Mr R. D. Reed for invaluable assistance with microcinematographic technique. The work was carried out during the tenure of a Nuffield Foundation Research Fellowship.

During the summers of 1969–71, 554 ground squirrels belonging to six species (115 Spermophilus columbianus, 46 S. franklinii, 13 S. lateralis, 327 S. richardsonii, 20 S. tridecemlineatus and 33 S. undulatus) were sampled for trypanosomes. Natural infections were recorded in all but S. lateralis.In 1969 and 1970 the prevalences of infection were approximately equal within, but varied between each species of ground squirrel. In 1971 the prevalences of infection increased for all host species sampled. Trypanosomiasis was detected in twice as many ground squirrels when the haematocrit centrifuge technique was used for diagnosis instead of stained thin blood films.In S. richardsonii the prevalences of infection varied from month to month but showed the same trends in both 1969 and 1970. Prevalence was lowest in May and highest in June. It is suggested that susceptible juveniles accounted for the high prevalence in June.

Five species of acephaline gregarine parasites – Apolocystis pilosa Meier from Lumbricus castaneus, L. festivus, L. rubellus and L. terrestris, Monocystis arcuata Boldt from L. castaneus, Nematocystis gracilis Berlin (= N. anguillula var. gracilis) from L. castaneus and L. rubellus, Zygocystis cometa Stein from Allolobophora caliginosa and Z. eiseniae Loubatieres from Eisenia foetida – identified during the present work are new to the British record.

The characteristics of two other monocystids, N. lumbricoides Hesse and N. lumbricoides var. pilosa Meier are identical apart from the presence of short ectoplasmic hairs on the latter trophozoite's body. Since the presence of ectoplasmic hairs which are projections on the trophozoite's body is often utilized in gregarine speciation, the hairy and the hairless monocystids should be described separately.

Berlin (1924) identified N. anguillula var. gracilis from the seminal vesicles of Lumbricus terrestris, L. rubellus and L. castaneus. This trophozoite should have been described as a separate species, N. gracilis Berlin and not as a variety of a totally different species originally described by Hesse (1909) from a host, Pheretima rodericensis, a megascolecid oligochaete, not found in Europe.

The writer wishes to express his sincere appreciation to Dr Anne Terry for her advice and useful suggestions, and to Mr D. Etherington, the head of department, for his encouragements throughout this research period.

Detailed descriptions are given of the larvae of the three species of British metastriatan ticks, with particular reference to the arrangement and dimensions of setae.

Schizont-infected red blood cells (SI-RBC) from Plasmodium berghei-infected mice contain between 2 and 10 times as much sialic acid as uninfected RBC from the same blood (99–550 μg/1010 RBC versus 33–65 μg/1010 RBC). Total RBC samples from infected animals containing up to 63% ring- and trophozoite-infected cells had identical sialic acid contents to purified RBC samples (of < 3% parasitaemia) from the same blood (52–64 μg/1010 RBC). We conclude that RBC containing immature parasites have the same sialic acid content as uninfected RBC from infected blood and that total cellular sialic acid increases during maturation to the schizont stage. Uninfected RBC from infected blood had 25–50% as much sialic acid as normal mouse RBC (33–65 μg/1010 RBC versus 126 μg/1010 RBC). There were no qualitative changes in RBC sialic acids, all RBC samples having 60–70% N-acetyl neuraminic acid, 30–40% N-acetyl-9-O-acetylneuraminic acid and 5–10% N-gly colylneuraminic acid. The quantitative changes we observed during infection must reflect changes in murine sialoglycoconjugates, as we have shown elsewhere that Plasmodia do not synthesize or contain sialic acids. Since the sialic acid composition of mouse serum glycoconjugates is quite different to that of the RBC fractions studied here, the quantitative data suggest that part of the sialic acids of the uninfected RBC has been transferred to SI-RBC. With higher molar ratios of periodate to substrate than generally used, we were able to radio-isotopically label normal murine sialoglycoproteins on SI-RBC and purified uninfected RBC from infected blood by the periodate/NaB3H4 method. Several new proteins were then tritiated with SI-RBC but these proteins may be intracellular and could even lack sialie acid.

The status of Trypanosoma suis was held in doubt from the time it was first seen in 1905 until it was re-discovered and carefully studied in the Belgian Congo in 1954.

A description is given of the morphology of single and dividing forms of T. suis as seen in stained thin films made from the blood of infected pigs, and a selection of these is illustrated by line drawings. Briefly this trypanosome is short and stumpy with a free flagellum.

A biometrical study was made on 200 organisms, showing a normal length distribution with a range from 8·5 to 18·5μ, and mean = 14·43μ.

The monomorphism of the trypanosome is verified, and—because of its development in the salivary glands of Glossina—its systematic position as a monomorphic subgroup of the Brucei group is confirmed.

I am much indebted to Dr C. A. Hoare, F.R.S., for the loan of the blood films used in this study and for his interest in the work. I am also grateful to Professor P. C. C. Garnham for providing me with accommodation and equipment at the London School of Hygiene and Tropical Medicine.