The sporozoites of Eimeria acervulina and E. maxima when injected into the caeca of chickens fail to produce infections. Sporozoites of E. mivati injected into the caeca invade the walls and the life-cycle is completed. These observations are discussed in their relation to the fate of sporozoites injected into the allantois of chick embryos. The possible use of these techniques in confirming the identity of a species is discussed.

We wish to thank Mr B. J. Millard for technical assistance with the preparation of the sporozoites.

Two interesting and unusual Spiruroid parasites have been reported from the intestines of marine fish. These are referred to the new genera and species, namely, Bulbocephalus inglisi and Cestocephalus serratus. The former is characterized by a globular head and the muscular oesophagus has two bulbs in its most anterior part. The glandular portion of this oesophagus is 20–25 times as long as the muscular part. The diganosis of Cestocephalus serratus is mainly based on the presence of an oblong head which is covered anteriorly by lobe-like structures in the manner of bothridia in some Cestodes. A new subfamily (family Spiruridae) has been proposed to accommodate Bulbocephalus gen.nov. The family or subfamily diagnosis of Cestocephalus gen.nov. has been restricted at present due to the paucity of material.

The writer wishes to express her gratitude to Professor J. J. C. Buckley for his interest throughout this work.

Previous studies on variation in size in the immature stages of ixodid ticks have been based on the assumption that the progeny of single females constitute a homogeneous population.

From the present work on the immature stages of Hyalomma anatolicum anatolicum, and by following larvae and nymphs to the adult stage, it is clear that there are two size groups of larvae and nymphs which reflect their potential sexuality. Larvae and nymphs which give rise to males are smaller in size than those which produce females. This size difference of the immature stages has other implications, for larvae and nymphs destined to become males imbibe, on average, about two-thirds the quantity of nutrients of those which yield females. Because of these apparent morphological and behavioural feeding mechanisms, which appear to be genetically determined, differences in physiological patterns of activity in the immature stages of the two sexes cannot be overlooked and may prove useful in elucidating the transmission of pathogenic organisms by larvae and nymphs.

We are grateful to Dr R. P. Chaudhuri for providing us with the original ticks from which our culture was started, and one of us (K.S.) to the Science Research Council for the provision of a research grant.

It has been shown that the 5th or adult stage of Trichinella spiralis stimulates strong immunity in mice. This was shown using a transfer technique and irradiated worms. A comparison between the immunity produced by a normal infection and one which has been irradiated is made and explanations offered to explain the fact that less immunity is stimulated by irradiated larvae.

I would like to express my gratitude to H.M. Treasury and to the Agricultural Research Council for financial support during the time that this work was conducted. I would also like to thank Professor W.I.B. Beveridge, within whose department this work was conducted, for the facilities provided. I would also like to record my gratitude to Dr W. C. Campbell for the many stimulating discussions we have had on the subject of Trichinella.

The body wall of the daughter sporocyst of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854, is shown by the electron-microscope to consist of an external syncytial tegument, lying on a basement membrane, and an internal cellular subtegument, which surrounds a body cavity containing developing cercariae.

The syncytial tegument has areas of dense cytoplasm alternating with sparse reticulate cytoplasm. The dense cytoplasm contains nuclei, a few mitochondria and secretory products which probably include a neutral mucopolysaccharide. This may be the precursor of the acid mucopolysaccharide in the sparse reticulate cytoplasm and on the surface of the daughter sporocyst.

Nutrients are probably absorbed through the outer plasma membrane of the tegument, pass through the sparse reticulate cytoplasm in the middle region of the tegument, the inner plasma membrane and basement membrane into the subtegument.

The ultrastructure of the tegument of adult and larval Digenea are compared.

We would like to thank Dr Gwendolen Rees for allowing us to examine the electron-micrographs of Parorchis acanthus. We are also grateful to Professor E. W. Knight-Jones for the provision of excellent working facilities and to the Science Research Council, for a grant to one of us (E.A.B.) which made the work possible.

Three species of the nematode genus Capillaria Zeder, 1800, namely C. exilis, C. ovopunctata and C. similis, are described from material collected from the intestines of four avian hosts—Turdus merula, T. viscivorus, T. ericetorum and Sturnus vulgaris. C. similis is fully described for the first time. A consideration of these species reveals that the original description of C. exilis is inaccurate and that some revision is necessary in the systematics of this and of the other two species.

Four species of Eimeria from fowls were able to develop in chicken embryos following the inoculation of sporozoites. Three species (E. brunetti, E. mivati and E. tenella) were able to complete the whole of their endogenous cycle in embryos. E. necatrix developed to late schizogony, E. acervulina and E. maxima did not develop.

The life-cycles appeared to be delayed, and in the case of E. tenella embryo mortality was associated with heavy parasitism of the chorioallantoic membranes. Oocysts recovered from urate deposits in the allantoic cavity sporulated normally and induced infections in chickens.

Attempts to infect turkey and quail embryos with E. tenella or chicken and turkey embryos with E. stiedae were unsuccessful.

The implications of the findings are discussed.

I wish to thank Dr C. Horton-Smith for his encouragement and guidance with this work; Dr M. E. Rose for help in the preparation of the manuscript and Mr B. J. Millard for careful technical assistance.

Partly developed strobila of Echinococcus granulosus from a 28–38 days infection in a dog have been brought to maturity by culturing in both liquid and diphasic media.

Surface-sterilization of the worms from dogs was achieved by use of antibiotics. Maturation was most successful in a diphasic system consisting of Parker 199+10% inactivated bovine serum over a solid base of coagulated bovine serum and a gas phase of 8% O2+5% CO2 in N2.

In the most successful results in diphasic media, a 28-day-old strobila reached maturity after a further 14 days in vitro culture, and a 35-day-old strobila matured after 6 days culture.

Ova produced in vitro showed activity but were not tested for infectivity. Abnormalities developed in some cultures, especially in monophasic media.

This work was supported by the Australian Wool Board, the World Health Organization and U.S. Public Health Service Research Grant no. E 4707–03.

Chickens which have recovered from an initial Histomonas infection are better hosts for Heterakis gallinarum than chickens which are fully susceptible to Histomonas. Not only do they support more nematodes but the immature worms, measured 12 and 14 days after infection, are larger.

Acknowledgements are due to Miss C. N. Hebert who carried out the statistical analysis and to Mr C. C. Norton for technical assistance.

In the mouse pinworm, Aspiculuris tetraptera, the basic features of the process of osmotic regulation is similar to the process in other nematodes such as Parascaris equorum, Rhabditis terrestris and Hammerschmidtiella diesingi. The ability to osmoregulate is, however, utilized more effectively in a hypertonic than in a hypotonic solution.

The body fluid is isotonic with 35 % sea water. The relative accuracy of this value is confirmed by direct measurements of the depression of freezing point of the body fluid. This is approximately 0.68–0.69 °C, which is approximately 0.12 % NaCl, which is higher than the value for Ascaris (= 0.655 °C).

My thanks are due to Dr D. L. Lee for helpful discussions on some aspects of this study.

Young and old rediae of Parorchis acanthus Nicoll, from the digestive gland and gonad of Nucella lapillus (L.) have been described. The young redia has an anterior collar-like fold and mid-ventral birth papilla the movements of which are controlled by a special arrangement of muscles. The birth papilla is ‘solid’ but in older rediae is replaced by a pore. The pharynx is of fairly uniform size irrespective of the size of the redia and the intestine, in the young redia, is relatively muchlarger than in the older redia which facts suggest that relatively more food may be absorbed by the mouth in the young stage. The redia cavity develops as a slit in the central cell mass. As it enlarges the intestine remains close to the dorsal wall and developing embryos are carried, among the cells, towards the surface dropping into the cavity, later, to complete their development. Up to fifty-five cercariae may be present in a redia. Simple nervous and excretory systems are present.

The tegument consists of one layer; the surface bears numerous unusual branched microvilli. The syncytial protoplasm contains numerous electron dense mitochondria, vacuoles and granules. Half-desmosomes, not recorded for any other parasitic platyhelminth, occur fairly regularly on the lower limiting layer. Below the uninterrupted basement membrane are circular and longitudinal muscles and, lining the cavity, two or three layers of flattened cells containing numerous mitochondria, agranular and granular endoplasmic reticulum and Golgi complexes. Large lipid globules accumulate in the cells.

It is suggested that, in the older redia, active transport of nutrient materials through the tegument may take place.

Studies of the cuticle of Aspiculuris tetraptera with both the light and the electron microscopes have shown that there are three basic layers, namely the cortex, which consists of an outer and an inner layer, the matrix layer and the fibre layer; the latter is made up of three layers. There is, in addition, a thin osmiophilic superficial membrane on the surface of the cuticle; this membrane is seen only with the electron microscope.

It is shown that the major structural protein of the cuticle, although showing no axial periodicity, is collagen; the collagen is associated with hyaluronic-acid- and chondroitin-sulphate-containing mucopolysaccharides.

Evidence is presented for the existence of two centres of protein synthesis (collagen fibrogenesis) in the cuticle of A. tetraptera, Syphacia obvelata and Ascaris lumbricoides. These centres are located in the inner cortex and the hypodermis. The cuticle is thus very active metabolically.

I wish to acknowledge with thanks the facilities afforded me at the Molteno Institute during the course of these studies by the Director, Dr P. Tate. My thanks are also due to Dr D. L. Lee for his encouragement and helpful discussions during the investigations.