1. As an intermediate host of the hydatid tapeworm in boreal North America, the moose is of relatively greater importance than other indigenous cervids (white-tailed deer, wapiti, barren-ground caribou) primarily because of a higher rate of infection in different individuals and the fertility of the hydatid cysts.

2. The European reindeer introduced into north-western Canada is of considerable importance as an intermediate host where it occurs locally.

3. Timber wolves are the important definitive hosts; no infections occurred naturally or were produced experimentally in the bobcat, Canada lynx, raccoon, fisher, marten, striped skunk or European ferret.

4. A description using biological and morphological criteria is presented for Echinococcus granulosus granulosus in dogs, sheep and other domestic animals, E. g. borealis subsp.nov. in timber wolves, moose and other cervids indigenous to North America, and E. g. canadensis Webster and Cameron, 1961, in dogs and reindeer introduced into north-western Canada from Laplandic Norway.

5. The rate of cystic growth, scolex production, infectability of timber wolves and dogs and prepatent period are similar for all three subspecies.

6. E. g. borealis reached a gravid state in experimental red foxes (Vulpes fulva).

7. Hydatid cysts developed only rarely in sheep fed eggs of E. g. borealis or E. g. canadensis.

8. Eggs of E. g. granulosus produced only one viable hydatid cyst in a series of experimental red deer (Cervus elaphus) and fallow deer (Dama dama).

9. E. g. granulosus, E. g. borealis and E. g. canadensis are morphologically distinct, the most distinctive characters occur in E. g. canadensis.

10. Besides the above and E. multilocularis, other species in Echinococcus are little known. Those recognized as being currently valid are E. lycaontis, E. ortleppi, E. felidis, E. cameroni, E. oligarthrus, E. cruzi and possibly E. patagonicus.

The writers wish to thank Sir Charles Hercus and the other members of the Hydatid Research Committee for their interest and encouragement in the present study. Valuable discussion in the early stages of this work was had with Prof. A. M. Fallis, Director, Department of Parasitology, Ontario Research Foundation. Much of the field work was done with various members of the Ontario Research Foundation; Institute of Parasitology, McGill University; Canada Department of Agriculture; and Canada Department of Northern Affairs and Natural Resources, to whom we extend our thanks. Norwegian material was kindly provided by Dr Sven Skjenneberg, Statens Veterinaera Laboratorium for Nord-Norge. Technical assistance was provided by Messrs G. D. Page, D. V. Weston, Miss L. A. Duncan and Mrs B. R. Clarke.

1. A 12·8% incidence of hydatid infections occurred in 709 horses examined in England. By contrast, hydatid cysts do not occur in horses in New Zealand where Echinococcus granulosus granulosus is common in sheep, cattle and swine.

2. Experimentally, scolices from hydatid cysts from English horses reached a gravid state in laboratory dogs. It was not possible to infect horses with E. g. granulosus of sheep-dog origin, and only one of two sheep became infected with two cysts following the ingestion of eggs of English horse-dog origin.

3. Our observations, together with those of others on secondary hydatid cyst formation, indicate that the two types are not only biologically but morphologically distinct.

4. In the horse-dog worms, the cirrus sac tilts anteriorly at an acute angle; the testes (about 35) are distributed throughout the proglottid with two or three rows posterior to the vitelline gland, and persist in proglottids when some mature eggs are present; the average length of the rostellar hooks is greater than in E. g. granulosus.

5. It is proposed that the horse-dog material be named E. g. equinus subsp. nov.

6. Rostellar hooks from cysts in British cattle resembled morphologically those from horses, while those from a British sheep and from man were like the hooks from hydatid cysts in man and livestock in New Zealand.

7. A red deer, hedgehog and European rabbit were not infected artificially following the ingestion of eggs of E. g. equinus.

Mr J. T. Briggs, Chief Public Health Inspector, Public Health Department, Bently, Doncaster, England, was responsible for the inspection of the British horses reported in this paper. We are indebted to Mr Briggs for this courtesy and for sending us fresh hydatid cysts from horses for experimental purposes. Mr N. Aitken was responsible for maintaining the experimental horses in an area of New Zealand known to be free of E. granulosus. Our thanks are also due to Messrs G. D. Page, D. V. Weston, Miss L. A. Duncan and Mrs B. R. Clarke for their able technical assistance.

Between January 1961 and March 1962 the writer made a parasite survey of twenty-three Wilson's Snipe, collected in Northern Colorado. Eleven birds were found to be infected with a previously undescribed species of hymenolepid cestode. The following description of a new species is based upon twenty-seven complete specimens recovered from the small intestines and caeca of these snipe.

A list of the genera of the family Caryophyllaeidae known from India is given. Crescentovitus biloculus gen.nov., sp.nov. from the coelom of the siluroid fish, Heteropneustis fossilis, is described and its systematic position discussed. An up-to-date key to the genera of the subfamily Lytocestinae is included.

I desire to express my deep gratitude to Professor M. A. Moghe for his helpful criticism in the preparation of this paper, and to Mr N. A. Shastri, Principal M.M. College of Science, Nagpur, for the kind co-operation extended to me. My thanks are due to Mr S. C. Theophilus, Head of Botany Department, Hislop College, Nagpur for helping me in various ways.

1. An account is given of the seasonal occurrence and maturation of Triaenophorus nodulosus, based on the examination of the worms from 104 pike taken in Llyn Tegid from December 1957 to October 1959.

2. The plerocercoids of T. nodulosus were found in the livers of the perch of Llyn Tegid. Infective plerocercoids were found throughout the year, and it is considered that invasion of the pike, also, occurred throughout the year.

3. The annual cycle of maturation of T. nodulosus described by other workers is confirmed. Currently, five arbitrary stages of maturity were recognized, and the incidence of each of these stages during each month of the investigation is given. During June to September the worms were of plerocercoid-form, from October to December genital development occurred and the first eggs were observed in the uteri in December. Egg liberation was at a peak from April to May, and by June the population of matured worms was lost.

4. A non-linear relationship was found between the length of the pike and the numbers of worms occurring in the intestines of these fish. This phenomenon was related to the feeding habits of the pike; the medium-sized most heavily infected pike were eating the largest number of the perch containing the plerocercoids.

5. It was found that although invasion of the pike by plerocercoids of T. nodulosus occurred throughout the year, there was no increase in the numbers of worms in the pike intestines, to a maximum, at any time of the year, rather there was a more or less constant number of worms in pike of given length at all times of the year. It is suggested, therefore, that a dynamic equilibrium exists between gain of plerocercoids and loss of worms from the pike intestines at all times.

6. Factors affecting the change from plerocercoid to a mature worm are discussed. It is suggested that an experimental approach is needed.

I am grateful to the Welsh Land and Agricultural Sub-Commission for permission to net Llyn Tegid, and to Captain G. H. A. Boyle of the Sub-Commission for his help in the capture of the pike. I also wish to thank Professor R. J. Pumphrey in whose Department this work was carried out, Dr P. M. Sheppard for statistical analyses, Dr J. W. Jones and Mr S. Prudhoe (British Museum, Natural History) for discussion of the manuscript. The work was carried out during the tenure of a Department of Scientific and Industrial Research studentship.

The form of the egg, the structure of the oncomiracidium and the subsequent development of Entobdella soleae, a monogenean skin parasite of the common sole, are described. The reproductive organs develop in a constant sequence and the parasite is protandrous. Glands of Goto were observed in post-oncomiracidia of all ages.

The early embryo of E. soleae possesses eight pairs of marginal hooklets and two pairs of hamuli. One pair of hooklets, centrally situated on the adhesive organ, undergoes metamorphosis and becomes the pair of accessory sclerites associated with the hamuli in the adult.

My thanks are due to Dr J. Llewellyn for continued advice and criticism. The work was conducted during the tenure of a Fishery Research Training Grant from the Development Commission.

The anatomy of the oncomiracidium of Capsala martinieri, a monogenean skin parasite of the sun fish Mola mola, is described and compared with that of the oncomiracidium of Entobdella soleae, a skin parasite of the common sole Solea solea.

The oncomiracidium of C. martinieri is characterized by the occurrence of an extensive bilaterally symmetrical and constant pattern of body pigment of unknown function.

Both individuals of a pair of Diplozoon paradoxum Nord., 1832, when parasitizing the gills of Rutilus rutilus, are normally attached to the same hemibranch but never to the same surface of one primary lamella. A preference is shown for attachment to certain gills and also to particular locations on the gills.

Diplozoon paradoxum displays asymmetry of its haptor when attached to the gills of the roach but the haptor assumes bilateral symmetry when unattached. As in Discocotyle, this impermanent asymmetry is facultative to the left or right, dependent upon the incidence of the gill-ventilating current, so that the body of a worm will present the least amount of resistance to the water as it passes across the gills. It is probable that impermanent, facultative asymmetry occurs in other species of the genus Diplozoon, and the usefulness of the asymmetrical nature of the haptor as a taxonomic criterion is therefore extremely limited.

It is a pleasure to record my thanks to Dr F. G. Rees, University College of Wales, Aberystwyth, for her encouragement and guidance and to Dr J. Llewellyn, University of Birmingham, for his valuable help and critical reading of the manuscript. I am indebted to Mr D. Haigh for supplying me with fishes. This work was done while receiving a grant from the Department of Scientific and Industrial Research.

The adhesive apparatus of Diplozoon paradoxum consists of four pairs of clamps and a pair of small hooks which apparently persists from the larval stage. The sclerotized framework which supports each clamp bears great resemblance to that of a Discocotyle clamp but certain differences, particularly in the fair-lead region, may make it mechanically more efficient.

A clamp of Diplozoon paradoxum operates on an extrinsic muscle-tendon-fair-lead-hinged-jaws principle as do the clamps of Discocotyle, Plectanocotyle and Kuhnia. It appears likely that other species of Diplozoon will be found to possess this clamping mechanism despite statements to the contrary.

It is a pleasure to record my thanks to Dr F. G. Rees, University College of Wales, Aberystwyth, for her encouragement and guidance and to Dr J. Llewellyn, University of Birmingham, for his valuable help and critical reading of the manuscript. This work was done while receiving a grant from the Department of Scientific and Industrial Research.

Outdoor observations were made on the rate of development of the free-living stages of H. contortus at different times of the year, and on the migratory activities and longevity of the larvae in faeces, on herbage and in soil.

The effects of temperature and humidity on the survival and development of eggs and larvae, both in faeces and when separated from the faeces, were studied in the laboratory.

The results of these observations are discussed in relation to the heavy mortality of the free-living stages of H. contortus and to the transmission of infection in the field.

Strongyloides papillosus is found to be very common in the Lucknow area where 90% of the sheep are infected. The life-cycle is predominantly indirect, or heterogonic. The development of mature free-living adults takes place between 20° and 37° C., and 34° C. is the optimum temperature. At a temperature of 25° C., the percentage of free-living adults is 60–65 in summer (March to November) and practically 100 in winter (December to February). Immature females can develop at 40° C. in summer, but not in winter, under laboratory conditions.

Inhibition experiments in a hot oven incubator with varying percentages of humidity, and in a humidity chamber incubator with constant 100% humidity, maintained at temperatures varying from 40° to 50° C., show that in the humidity chamber incubator mature free-living adults develop at 34° C. after incubation for 12 hr. at 40° C., after 4 hr. at 42° C., after 2 hr. at 45° C. and after 15 min. at 50° C. The hot oven incubator allows mature free-living adults to develop at 34° C. after 8 hr. at 40° C., after 2 hr. at 42° C., after 1 hr. at 45° C. and after 15 min. at 50° C.

The present paper is concerned with the description of six species of gregarines which are all parasites of British earthworms; they are: Apolocystis herculea (Bosanquet, 1894), A. lavernensis sp.nov., A. perfida sp.nov., A. rotaria sp.nov., A. spinosa sp.nov., A. villosa (Hesse, 1909) Cognetti, 1923. The observations upon which these descriptions are based form part of a larger survey of the monocystid fauna of several British earthworm species from the Cardiff area. The methods used are fully described in a previous paper (Rees, 1962).

1. An account is given of the intensity and incidence of infestation of the scorpaenid redfish, Sebastes marinus and S. mentella, by the parasitic copepods Peniculus clavatus, Sphyrion lumpi and Chondracanthopsis nodosus on three fishing grounds in the eastern North Atlantic, namely Iceland, Bear Island and the Barents Sea.

2. Peniculus clavatus was found to be a rare parasite on both species of redfish in the eastern North Atlantic. Adult female parasites were found during the months from September to February only; they were usually attached to the pelvic or dorsal fins of the host causing little damage.

3. Sphyrion lumpi was found to be a comparatively rare parasite on the deep-water Sebastes mentella throughout the eastern North Atlantic but it was found on S. marinus in the vicinity of Bear Island only. It seems justifiable to regard the Bear Island grounds as a centre of abundance of Sphyrion lumpi in the eastern North Atlantic. Adult female S. lumpi tended to infest medium-sized redfish more often than smaller or larger fish.

4. The infestation of Sebastes marinus and S. mentella by Chondracanthopsis nodosus has been examined in some detail and attention directed to the influence on infestation of the host species, geographical distribution, body length, age and sex of the host, and seasonal variations. The distribution of female C. nodosus within the gill chamber of the two species of redfish is described; it appears to be related to the need of the parasite to secure a protected and spatially limited habitat out of the mainstream of the ventilation current through the gill chamber.

5. The ecological relationships between Sebastes marinus and S. mentella and the three species of parasitic copepod are described together with the possibility of using these and other parasites as indicators of the host's mode of life. It is concluded that Chondracanthopsis nodosus and Sphyrion lumpi merit more detailed and extensive study as possible parasitological indicators of different stocks of redfish.

I wish to express my thanks to Messrs Jackson Mills Ltd., Fish Merchants and Curers, Hull, and to the Officer-in-Charge, D.S.I.R., Humber Laboratory, Hull, for their generous assistance in making redfish available for examination. I am also most grateful to Miss E. C. Howard, Librarian, Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, for her invaluable assistance in providing certain otherwise unobtainable references in the literature.

1. Defence reactions to metazoan parasites have been reported in fourteen orders of insects. The observations are brought together and reviewed in the first part of the paper.

2. Examination of the various accounts that have been given shows that blood cells are always involved in insect defence reactions. They act by forming a cellular capsule, from which a connective-tissue envelope is usually developed, and in which melanin is often deposited.

3. The reaction of the epidermal cells at perforations made by parasites is of the nature of wound-healing, and plays no part in defence against metazoan parasites after they have entered the body.

4. Although several other tissues have been implicated, there is insufficient evidence to show that any of them make defence reactions, their response being limited to processes of regeneration.

5. It is concluded that the blood cells of insects are their only known agents of defence to internal metazoan parasites.

6. The principal groups of metazoan parasites infesting insects are considered in the third part of the paper, in order to see how the defence reactions made to them are related to their mode of attack and to the nature and consequences of their parasitism.

7. Most parasites elicit a defence reaction when they are in unusual hosts.

8. Some parasites, at certain stages of their life-history, are able to avoid eliciting a defence reaction in their usual hosts.

9. Some parasites elicit a defence reaction in their usual hosts but are able either to endure it in a dormant state or to resist it.

10. General problems of host specificity in relation to defence reactions are discussed. It is concluded that analysis of the stimuli that produce defence reactions has not yet gone far enough to explain the phenomena.

11. The effects of insect defence reactions on metazoan parasites range from no perceptible effect to destruction of the parasite.

12. The defence reactions of insects are influenced by the species, genetic strain, stage, instar, size, health and physiological state of the host; and by the species, genetic strain, physical and physiological activity, and health of the parasite. Environmental temperature and the presence of other parasites of the same or different species also have effects on the reactions.

13. A brief survey of defence reactions made by invertebrates other than insects shows that encapsulation has been reported in Annelida, Mollusca, Crustacea, Acarina, and larval echinoderms. So far as it goes, the survey does not reveal in these other groups any reaction to metazoan parasites of a kind radically different from the reactions observed in insects.

14. The historical development and present state of our knowledge of insect defence reactions is traced.

15. The reactions made by insects to innocuous parasites are of theoretical interest but of little consequence to the species concerned. It is their effect on potentially dangerous parasites that determines the value of defence reactions. Consideration of the evidence suggests that the protection afforded to insects by their defence reactions is greater than has been generally supposed.

16. The review makes apparent many gaps in our knowledge of the phenomena. A few of the outstanding problems are mentioned.

I am indebted to Mr R. T. Hughes of the Balfour Library for helping me to obtain journals not available in Cambridge; to Mr M. J. Ashby for the photography necessary in the preparation of the figures; and to Miss G. M. Edwards for her careful typing from my manuscript. The paper would not have been completed without the goodwill and assistance of two persons: Professor D. Keilin, F.R.S., encouraged me to continue and finish it when my effort flagged; my wife not only gave me positive help in many ways but also exercised great forbearance in allowing me to devote vacations and spare time to it.

1. Different shapes and forms found in Toxoplasma gondii are associated with reproduction and growth. The functions of the toxoneme and the conoid are discussed.

2. A new structure, ‘lamella spiralis', is described in relation to the nucleus and the endoplasmic reticulum.

3. T. gondii reproduces either by dividing into two (binary fission) or by multiple division (schizogony), and by a type of endogenous budding. In the latter case small portions pinched off from the nucleus are rounded up to form several small organisms named ‘morulae'.

The author gratefully acknowledges the interest and valuable suggestions of Dr G. A. Gresham, M.D., who supervised this work; Dr J. M. Davis and Mr F. Allen, who were kind enough to read the manuscript critically, and Mr W. A. Mowlam for his technical help and advice on fixation techniques.

This work was carried out during the tenure of a research scholarship awarded by the United Kingdom Department of Technical Co-operation and the Eastern Nigerian Government.

Since its discovery in France by Mégnin (1878), Cheyletiella parasitivorax has been found in many countries—on rabbits (Oudemans, 1906; Pillars, 1925; Ford, 1944; Mykytowycz, 1957a; Womersley, 1941), on the dog (Humphreys, 1958), fox (Kuscher, 1940), cat (Niggli & Teuscher, 1959; Davies, 1941), man (Olsen & Roth, 1947) and even in phoretic association with fleas (Cooper, 1946). Hirst (1917) was the first to find the species in Britain and there have been several more recent records from this country.

Sulphaquinoxaline fed at 0·0125%, w/w, in the food principally affects the development of the second generation schizonts of Eimeria adenoeides in turkey poults. Amprolium, at the same concentration, acts on the first generation. Both drugs appear to exert some effect on gametogony. The activity of sulphaquinoxaline against this species is inhibited by p-aminobenzoic acid, and the activity of amprolium by thiamine.

We are grateful to Mrs B. M. Mitchell and Miss C. Hitchcock for technical assistance and to Mr A. D. Speed for the histological preparations.

1. Certain aspects of the general morphology of Polymorphus minutus are described together with a detailed description of the body wall.

2. An additional layer of the body wall, the epicuticle, has been demonstrated. It appears to consist of acid mucopolysaccharide and may have a function of protecting the parasite from the enzymes of its host.

3. A histochemical investigation has been made of the layers of the body wall and it is concluded that lipoprotein is one of the main structural components.

4. The distribution of the activity of the two enzymes, non-specific esterase and alkaline phosphatase, has been studied throughout the animal and the activity of a third enzyme, leucine aminopeptidase, has been detected in the body wall.

5. It is suggested that all the layers of the body wall, with the exception of the cuticle and epicuticle, are of metabolic importance. The striped layer may be connected with absorption and the felt and radial layers may be involved in the further metabolism of absorbed compounds.

6. The results obtained are used to formulate a possible structure of the surface of the parasite which would facilitate the absorption of nutrient substances through the body wall.

I am grateful to Dr P. Tate for advice and encouragement during this work, Dr R. J. Tatchell for helpful discussions, and Dr D. L. Lee for criticising the manuscript and Mr T. M. Warwick, Department of Zoology, University of Edinburgh for providing material.