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. The functional anatomy of the ducts associated with Mehlis's gland in the echinostome Artyfechinostomum mehrai (Faruqui) recovered from a girl has been described.

2. The mechanism and histochemistry of egg-shell formation are described and discussed.

Appreciation is extended to Dr V. S. Raghunathan, M.D., Physician and Superintendent, and Dr T. Sreenivasan, M.D., of King George Hospital, Visakhapatnam, for their kind co-operation and the gift of specimens of A. mehrai. My thanks are due to Professor P. N. Ganapati for facilities and encouragement.

The development of Amplicaecum robertsi has been followed from the egg to the adult stage using laboratory mice and rats as intermediate hosts. The eggs were found to be resistant to desiccation and would develop under water; they were infective to mice after culturing for 18 days after removal from the uterus.

Completion of the first moult occurred after hatching of the eggs in the intestine. Within 6 hr. of infection second-stage larvae had reached the liver. They also appeared in the lungs and carcass, but after 2 days were mostly confined to the liver.

At 5–7 days after infection larvae underwent a period of lethargy followed by the second moult and the third-stage larvae commenced a period of growth reaching a length of 79 mm. at 28 weeks after infection in the liver of mice. In rats the growth of the larvae was slower for the first 2 months, but eventually they reached more or less the same proportions as in mice. The intestinal caecum appeared at a length of 3–4 mm., but there was no development of the reproductive organs throughout the third stage and no evidence of the third moult in rodents.

Fifty carpet snakes were autopsied and searched for larvae and adults of A. robertsi; in two snakes third-stage larvae were found in the aorta; in one snake the third moult was observed in the wall of the stomach and oesophagus; in three snakes the fourth moult was observed in the wall of the stomach; in twenty-six snakes adults were found.

Experimental infection of laboratory-reared carpet snakes showed that infection with embryonated eggs resulted in second-stage larvae in the tissues which did not develop further. Infection with third-stage larvae, resulted in two distinct migratory patterns depending upon the maturity of the larvae administered. Larvae from the liver of laboratory rats which had been infected less than 12 weeks previously, migrated to various tissues, especially the aorta, of the snake, where they remained coiled in cysts filled with clotted blood for periods up to 112 days. Growth occurred within these cysts, but no evidence of moulting was observed. In contrast, larvae from the liver of laboratory rats infected 12 weeks or more previously, and from mice infected for 8 weeks or more, underwent the third moult in the wall of the oesophagus and stomach of the snake.

With the onset of the fourth stage, the development of the reproductive organs became evident and continued during the fourth stage. It appeared that the fourth stage may occur in two phases, possibly depending on the size of the third-stage larva at the time of ingestion. Some experimental infections indicated that third-stage larvae may give rise to attached fourth stage larvae, probably capable of active growth. Other observations indicated that fourth-stage larvae may remain encapsulated in the wall of the stomach or oesophagus until sex differentiation is completed, after which the fourth moult occurs and the adult parasite emerges, leaving two sheaths of the same length within the capsule.

The functional significance of each of the larval stages is discussed and it was concluded:—that the first-stage larva is one of tissue differentiation, whereby development proceeds to the infective stage; that the second stage represents a migratory phase without structural changes; that the third stage represents a growth phase, characterized by considerable increase in size, but without further radical changes in differentiation.

In contrast, the fourth stage is characterized by absence of growth, inability to migrate, and by marked structural changes in the reproductive organs, whereby the sexes are differentiated. Evidently this development may take place while the fourth stage is attached to the wall of the stomach or oesophagus, or while the larva remains in the capsule in a state of quiescence.

The fourth moult may occur in the attached state, but usually occurs within the capsule. After it is completed, the adult may remain for an indefinite period within the capsule with the two sheaths of the third and fourth stage. The emergence of the adult worms may be influenced by the arrival of food in the stomach. Once this phase is initiated, both growth and reproductive activity ensue during the adult stage.

This work was financed by a research grant from the University of Queensland. The writer wishes to acknowledge the valuable assistance of Miss Ann Pritchard.

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.

The paper records the description of the morphology and taxonomy of a new genus and species of a Heterotrichous ciliate (family Clevelandellidae) found in the gut of the non-xylophagous termite Capritermes incola Wasm. (Termitidae) from Dharwar (India).

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.

Notocotylus is reported in Indian domestic fowl and the specimen assigned to the species N. attenuatus. The literature on this monostome genus is briefly reviewed and need for an examination of type specimens of some of its species is stressed.

Thanks are due to the Principal of the college for facilities provided and to the head of the Zoology Department, Lucknow University, for loan of some literature.

The morphology of the adult blood fluke Schistosoma hippopotami sp.nov. from Hippopotamus amphibius L. is described and compared with that of other species of the genus Schistosoma.

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.

Common (1952, 1954) found a mermithid that parasitized the bogong moth, Agrotis infusa (Boisd.) during its resting period on the walls of caves in Australia. Nematode material that he collected was given to Dr J. B. Goodey, Rothamsted Experimental Station, Harpenden, Herts, England, who found it to contain two species. This material subsequently was given to me, and on examination each species was found to be undescribed. A description of each follows with a suggested life cycle and some remarks on the unusual parasitism of adult insects by the mermithids. This material permitted a re-examination of the taxonomy of the genus Amphimermis Kaburaki & Imamura, 1932.

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.

A study of the changes in the worm burden in calves receiving daily doses of infective larvae of Ostertagia ostertagi indicates that the following processes occur:

(1) A constant loss of adult worms at a rate depending on the number present.

(2) An inhibition of development in the early fourth stage which depends partly on the presence of adult worms. This inhibition is not irreversible; larvae resume their development, the number which do so depending on the number present.

(3)A stunting of adult worms, those developing late in the infection failing to grow as large as those which developed earlier.

(4)An inhibition of ovulation, distinct from the stunting, which prevents worms developing later from becoming as prolific as those which developed earlier.

(5)A resistance to the establishment of newly acquired worms, which begins to operate after prolonged exposure to infection.

The loss of adult worms and their replacement by the further development of fourth stage larvae leads to a frequent exchange of populations of adult worms.

The effect of these phenomena in determining the course of the infection is discussed.

Whilst examining amphibian helminths collected from Pahang, Malaya, a hitherto undescribed species of Oswaldocruzia was found among them. In a previous paper (Yuen, 1962), I have recorded the only other Malayan species of Oswaldocruzia: namely O. hoepplii Hsu from Bufo melanostictus Boulenger, Rana macrodon Boulenger, and R. cancrivora Gravenhorst from various parts of Singapore.

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.

This paper records two new species of Amplicaecum from Malayan amphibians for which the following names are proposed: Amplicaecum communis sp.nov. and A. sandoshami sp.nov. A. communis is a common parasite in a number of Malayan amphibians, but A. sandoshami has been found only in Megophrys sp.

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.

This work contains the description of two new Coccidia parasitic in the South American lizard Cnemidophorus lemniscatus lemniscatus. One is identified as Eimeria flaviviridis americana subsp.nov., which is described and discussed in relation to the other species recorded from sauria. The other is Hoarella garnhami gen.nov., sp.nov., whose position in the family Eimeriidae necessitated a revision of the classification of the Coccidia Eimeriidae.

I wish to acknowledge the help and encouragement I received from Professor P. C. C. Garnham, in whose department this work was carried out. My thanks are also due to Dr Cecil Hoare for his private communications and assistance in the interpretation of histological specimens. The author is grateful for co-operation of the School's Photograph Staff and to members of the staff of the Department of Parasitology, especially to Mr P. E. Nesbitt for his valuable sections. Finally, the author is indebted to the Consejo de Desarrollo Cientifico y Humanístico de la Universidad Central, Caracas, for their assistance in the form of a scholarship during the tenure of which this work was produced.

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.