Earlier schemes of classification of the family Heterophyidae have been based in large part on such features as shape of body, presence of oral spines, number and position of testes, and distribution of vitellaria (Witenberg, 1929; Ciurea, 1933; Mueller & Van Cleave, 1932). Price (1940a) was the first to make extensive use of features of the ventrogenital complex (ventral sucker, gonotyl, genital pore, terminal male duct) and excretory bladder, and produced the first reasonable classification of both the family Heterophyidae and the superfamily Opisthorchioidea. In despite of the obvious significance of the rationale of Price's approach, later authors (Morozov, 1952, 1955; Yamaguti, 1958) have largely ignored the ventrogenital complex and recently discovered life-history data, and have used much the same sorts of features as earlier authors.

A survey of endoparasites of the Red Kangaroo (Megaleia rufa (Desmarest)) has been carried out in three geographically distinct areas of south-eastern Australia.

During a period covering 22 months, 464 kangaroos of different sexes and ages were collected. Alimentary canals and tracheae of all of them and blood and organ smears from 333 were examined for parasites.

A list of endoparasites of the Red Kangaroo encountered during the study and of others reported earlier is given. This includes three species of blood protozoa, two species of coccidia (Eimeria spp.), two species of cestode and twenty-one species of nematodes.

The numbers of some nematode species are analysed in relation to season, sex of host and age of host as expressed by length of tibia.

Two different patterns of age susceptibility of the Red Kangaroo to nematodes are recorded and it is suggested that these may be dependent upon the presence or absence of direct contact of the parasite with host tissue.

Distribution of nematodes in the stomach of the Red Kangaroo has been studied. Different species were found to occupy separate niches within the stomach.

A statistical test aimed at showing the correlation between severity of infection with some nematodes and condition of host expressed by the ratio: body weight — stomach content/tibia length showed only a very weak negative correlation.

Alimentary canals of 100 sheep and thirty-five wild rabbits sampled simultaneously in the same area were found to be infected with only small numbers of worms.

No parasites injurious to domestic stock were found in the kangaroos examined.

Male specimens found with females of Spinitectus oviflagellis Fourment, 1884, in the intestine of Gadus merlangus have been described and compared with two other males of Spinitectus. Considering the differences they are regarded as males of S. oviflagellis.

The histological anatomy of the female reproductive system of an oxyuroid nematode, Aspiculuris tetraptera, Schulz, has been described.

The process of egg-shell formation in this animal has been followed in detail while the structural and chemical characteristics of the egg-shell have been studied by histochemical and other methods. It is shown that there are three layers: a lipoprotein layer, a ‘chitinous’ layer and the so-called vitelline (glycosidal) membrane. Evidence is presented for the exogenous origin of the lipoprotein layer: this being formed by the cells of the upper uterus which are shown to be secretory.

The question of quinone-tanning in the egg-shell of A. tetraptera and in other oxyuroids and ascarids is considered. It is shown that neither a polyphenol oxidase nor a high concentration of phenolic substances (apart from protein tyrosine) exists in this system. The significance of these and other observations is discussed in relation to the mechanism of tanning as elucidated in insects and trematodes.

I have to acknowledge with gratitude the support of many during these investigations. To Dr P. Tate for his encouragement and provision of facilities at the Molteno Institute; to Dr D. L. Lee, for much useful discussion and permission to refer to some of his unpublished electron micrographs of nematodes; to Professor J. D. Smyth, who kindly read through the manuscript; to the Cambridge Philosophical Society for a grant that made possible the translation of Fauré-Frémiet's classical study on Ascaris; and to the Department of Technical Cooperation for financial assistance.

1. The envelope surrounding Polymorphus minutus during its development in Gammarus pulex has been found to be a capsule produced by a wound healing haemocytic reaction of the host. The haemocytic reaction is stimulated when the parasite stretches the connective tissue serosa of the host's gut.

2. The capsule is a thin, acellular structure, consisting of a protein-carbohydrate complex like that constituting host connective tissue. This material is produced and deposited by the haemocytes.

3. The ability of the haemocytes to produce this protein-carbohydrate material is considered to be the mechanism which ensures the growth of the capsule during the subsequent development of the parasite in the haemocoel.

4. A second layer appears within the capsule just before the parasite reaches the cystacanth stage. This layer is believed to be produced by the parasite.

5. The relevant literature is reviewed, and it appears that the envelopes surrounding all developing Acanthocephala, which have been studied to date, are probably capsules originating in the manner described above.

I am very grateful to Dr P. Tate for advice and encouragement during this work, and to Dr George Salt, F.R.S., for helpful discussions and criticism of the manuscript.

One diphyllidean and five tetraphyllidean cestodes from Australian elasmobranchs are described and figured. Echinobothrium heroniensis sp.nov., from Himantura granulata (Macleay, 1883) possesses two groups each of 42 apical hooks, eight rows each of 25 hooks on the cephalic peduncle and ten testes in each proglottid. In Anthobothrium sexorchidum sp.nov. from T. lymna (Forskal, 1775) there are only six testes and the bothridium is irregularly divided into a number of shallow areolae while in Rhinebothrium himanturi sp.nov. from Himantura granulata there are 22 proglottids, 52 loculi and 19–20 testes. Comments are made on the taxonomy of Rhinebothrium sp., Spiniloculus mavensis and Yorkeria parva. The value of some helminths, especially cestodes from elasmobranchs, as an aid to the study of the taxonomy, biology and zoogeography of their hosts is briefly discussed with reference to some previous papers on this topic. Previous work on the cestodes of Australasian marine fishes is summarized briefly.

The structure of the spores of Encephalitozoon cuniculi Levaditi, Nicolau & Schoen, 1923, shows that it belongs to the Order Microsporidia Balbiani, 1882 and that the genus Encephalitozoon is a synonym for the older Nosema Nägeli, 1857. Therefore, the species of Microsporidia described from mammals are now: Nosema cuniculi (Levaditi, Nicolau & Schoen, 1923), Nosema rabiei (Manouelian & Viala, 1924) and Nosema chagasi (Torres, 1927). Another microsporidian in mammals is Thelohania apodemi (Doby, Jeannes & Rault, 1963).

In the intestine of freshwater fishes, two morphologically different types of diplomastigine flagellates have so far been found to exist: Hexamita salmonis (Moore, 1920) specific for fishes, and Spironucleus elegans Lavier, 1936, identical with the flagellate from amphibia.

The identity of the Spironucleus from fishes and amphibia has been demonstrated by infecting Pterophyllum scalare with flagellates from newts per os, per rectum and with contaminated food.

A redescription of motile stages of both Hexamita salmonis and Spironucleus elegans is presented, together with a list of existing findings of fish diplomastigines, and a brief discussion.

1. Pipunculus semifumosus (Kowarz) is an internal parasite of a number of common British Delphacidae. The life cycle and immature stages of the parasite are described.

2. The external and internal effects of parasitism on the delphacid host are described. Reductions in size and genital aberrations are related to the stage at which the host is attacked, and are most marked in female delphacids.