This paper describes a modification of the model for the transmission of schistosomiasis proposed by Macdonald (1965), which allows the snail host-locating efficiency of the miracidium to be taken into account. The modified model allows for a choice of miracidia efficiency. If it is assumed that the miracidia are inefficient hunters then the resulting model is very sensitive to perturbations; relatively small changes in snail numbers not only cause appreciable changes in the percentage of snails infected but result in attainment of the threshold (the point at which schistosomiasis ceases to be endemic). If, however, the miracidia are efficient snail hunters then the model is much less sensitive to perturbations; here the percentage of snails infected is much less affected by changing snail numbers, and the threshold is much more difficult to reach by reducing snail numbers. It is argued that, on the whole, the empirical data give more support to the latter model, although there are some circumstances under which the former model might apply. However, even with these modifications it is considered that the Macdonald model does not provide a satisfactory explanation of field observations.

In this study we examined the influence of salinity and temperature on egg development and miracidial emergence of the digenean, Himasthla militaris. In the range 2·1 to 34‰ salinity the eggs developed normally (i.e. no significant difference in the percentage embryonation), and miracidial emergence was only markedly inhibited in water with a salinity of 34‰. At 12 °C embryonation ceased; at 20 and 30 °C egg development as well as miracidial emergence occurred, but at 20 °C both processes progressed at a slower rate than at 30 °C.

The effect of temperature on the behaviour of the infective larvae of Trichostrongylus colubriformis has been investigated. Larvae acclimatized at 3°C or 20°C respond to sudden or gradual increases in temperature by coiling. Increased temperature may indicate a risk of exposure to desiccation and elicits a behavioural response which optimizes survival. Larvae are straight when inactive; coiling is an active response to specific stimuli. Larval activity is initiated by exogenous stimuli. Mechanical disturbance is a major stimulus, the response being affected by changes in temperature. Larvae acclimatized at 3°C or 20°C show a peak of activity at temperatures between 15 and 25°C.

Two tapeworms, Taenia saginata and Echinococcus granulosus, cause serious economic and human health problems in several parts of the world. Some of these Problems might be solved if a cheap, easy and safe vaccination could be developed. Before a vaccination against adult tapeworms can be developed it is necessary to know how intestinal tapeworm populations are controlled by immune mechanisms. For this purpose laboratory modeis have been used involving mainly species of Hymenolepis in rodents and especially H. diminuta in mice and rats, which will be referred to below.

There are few, if any, authenticated records of fossil helminths or even of the hard parts of ectoparasitic monogeneans. This means that theories of helminth evolution can be based only on indirect evidence and are unlikely to be confirmed or refuted by palaeontologists.

Currently three main areas of study provide evidence of evolutionary trends: (i) morphology, in its broadest sense; (ii) life-history studies; (iii) host spectra and geographical distribution.

The variation in the development of the reproductive system of female Schistosoma mansoni from single sex infections is described. Vitelline cell development was assessed by staining for phenolic substances and the development of Mehlis' gland and the ovary by electron microscopy. Although there was considerable variation in the development of worms from individual mice harbouring infections of the same age, the mean values indicated that there was a low level of differentiation and turnover of vitelline cells in worms 30–200 days post-infection. The proportion of females which possessed mature vitelline cells showed a general increase with age. The ovary was always in an immature stage but the development of Mehlis' gland showed some variation. The results suggest that the stimulus given by the male to the female is not necessarily to initiate development of the reproductive system but to increase the rate of development of the vitelline gland and to co-ordinate the development of the entire reproductive system.

The influence of genes in the major histocompatibility complex (MHC) of the guinea pig on the susceptibility to infection with the parasitic nematode Trichostrongylus colubriformis was investigated. Back-cross analysis of 2 lines of guinea pigs suggests that genes that map in or near the I region of the guinea pig MHC influence susceptibility to infection by the parasite. However, other genes, possibily not linked to the guinea pig MHC, may also be required for the full expression of susceptibility.

Coxal secretion of adult female Ornithodoros erraticus was found to contain a sex pheromone that induces in males of this species a mating response towards nymphs smeared with this secretion. Heterospecific coxal fluid from O. tholozani and O. moubata also elicited a mating response from O. erraticus males. Adult O. erraticus females did not evoke courting behaviour when immobilized or killed, but normal mating behaviour was regained when the immobilized females were freed – proving that both pheromone and recognition of a behavioural pattern are essential components of mating behaviour. Secretion of the sex pheromone appears by the 4th day after a blood meal and accumulates with time, thus increasing the number of attempted matings.

Studies on the multiple compact testes of Schistosoma mansoni have revealed 2 principal cell types: germinal and non-germinal cells. Two morphological forms representing different stages in the cytomorphosis of the sustentacular cells have been considered. The polymorphic sustentacular cells which are conspicuously stained with potassium permanganate contain abundant ribosomal endoplasmic reticulum, glycogen particles and ribosomal masses in comparison with the germinal component of the testes. Golgi complexes with associated secretory bodies and vacuoles are present in the cells. The cytoplasm of the sustentacular cells interdigitate between other cells in the testes. Based on their morphology, nutritive, supportive and phagocytic functions have been attributed to the sustentacular cells. The possible recycling of nutrients by the cells is discussed. It is suggested that the cells regulate the production of spermatozoa from a nutritive viewpoint and also that the translocation of nutrients from the parenchyma to the testes is facilitated by these cells whose cytoplasm extends directly adjacent to the basal lamina.

Corynosoma spp. (Acanthocephala) infection in ringed seals (Pusa hispida) is compared in spring and in autumn in the Bothnian Bay, northern Baltic Sea. The material consists of more than 13400 specimens: 7590 from the intestines of 13 seals captured in April and May 1978 and 5850 from 29 seals captured in October and November.

Corynosoma strumosum infection had approximately the same intensity in spring and autumn (mean 76 and 66 individuals/infected seal, maxmum 313 and 324 individuals, respectively). C. semerme specimens, on the other hand, were 37 times more numerous in spring than in autumn (504 compared with 136/infected seal, maximum 1700 and 1230 individuals, respectively). The ratio of C. strumosum to C. semerme was 1:6·3 in spring and 1:2·0 in autumn, as calculated from the total material. Corynosoma infection was more recent on average in spring than in autumn, as judged both from the proportion of males and immature females and from the distribution of C. semerme in the intestine. The feeding habits of the ringed seals and the rate of development of Corynosoma infection are discussed.

The genus Ostertagia, created on the basis of the presence of an accessory bursal membrane by Ransom (1907) and later placed in the family Trichostrongylidae Leiper, 1912, did not require reorganization until its revision by Orloff (1933). Although other related genera were described around this time the systematics of the whole group remained workable.

Irradiation doses of 800 rad. or less had no detectable effect on the subsequent development of unfed nymphal Rhipicephalus appendiculatus ticks. Doses of 1600 rad. or above impaired feeding and moulting and delayed the subsequent development of unfed nymphs. At 6400 rad. no ticks completed their moult. Unfed nymphal R. appendiculatus irradiated at 0, 400, 800 and 1600 rad. were applied to 3 cattle infected with T. parva (Kiambu 4). The Theileria infections in the salivary glands of the resultant adult ticks were assessed and it was found that irradiation doses of 800 rad. or less had little effect on the Theileria infections, but an–irradiation dose of 1600 rad. greatly reduced the level of infection. The numbers of salivary gland acini in ticks of this group were reduced but the percentage of infected acini was similar.

In 1979 the French population included 4200000 foreigners. While many came from European countries, mainly Spain, Portugal and Italy, a considerablc percentage came from the warmer belts of the earth: 20 % Algerians, 8 % Moroccans, 4 % Tunisians, 2 % black Africans. The total number has been on the decrease since 1978. However, metropolitan France has recently received, for political reasons, large groups from the Near East (Lebanese) and Southeast Asia (up to now 100000 Cambodians, Laotians and Vietnamese).

The structure and development of microgametocytes of Eimeria maxima from chicks killed during the 6th day of infection were examined using transmission and scanning electron microscopy. Initially, nucleoli disappear and the surface of the microgametocyte invaginates. This is followed by a condensation of the chromatin which then lies at the periphery of the nuclei. Concurrent with this, the flagella are formed and they project into the parasitophorous vacuole and internal invaginations. Eventually, the nuclei become more dense and are seen to protrude from the periphery of the gametocyte. The surface view of mature microgametocytes consists of a large number of closely packed flagella.

The histology of the reproductive system of male Moniliformis dubius has been studied by a variety of microscopical techniques. The system includes 2 testes from each of which arises a vas efferens. Products from the testis enter the vas efferens through openings present in the wall of the vas efferens. The testes are contained in a ligament sac and each testis is enveloped separately by an outgrowth of the ligament sac wall. There are 8 unicellular cement glands. The cement substance contains spherical electron-dense droplets presumed to be lipids. Saefftigen's pouch appears to be a hydraulic mechanism to regulate the turgidity of the wall of the bursal cap to effect successful copulation with female worms. The muscles attaching the genital sheath and bursa to the body wall are likely to be concerned with bursal eversion and inversion. Stimuli receptors connected to the genital nervous system are located in the penis and bursa.

A new form of parasitic copepod, Coelotrophus nudus gen. et sp. nov., is described based on the specimens recovered from the coelomic cavity of a species of Sipuncula, Phascolosoma scolops (Selenka and Be Man), at Sado Island in the Sea of Japan. The new genus is distinguishable from its closest allies, Akessonia, Siphonobius and Staurosoma, in the complete absence of appendages in the female and the absence of a mouth in both female and male. The incidence of infection is fairly high (34·1%) in this population of P. scolops at Sado Island. Histological studies of the gonads and microscopical examinations of the coelomic fluid of P. scolops collected monthly from April through December, 1979 have revealed that the presence of C. nudus causes sterility in its host. Some infected P. scolops also showed a marked decrease in the number of corpuscles in the coelomic fluid.

Biozzi mice of Selections 1 and 3, each exhibiting either high- or low- antibody responses to a wide range of antigens, were exposed to primary, secondary and tertiary infections of the nematode, Nematospiroides dubius. The course of these infections was followed by monitoring egg output and by examination of the worm burdens on the 14th day after each exposure to the parasite. When exposed to a primary infection, high and low responders were equally susceptible to the parasite, and the egg production of the infections was similar in all groups. However, when the mice were exposed to a 2nd infection of N. dubius, marked differences in the susceptibility of the hosts were seen. The high-responder mice of both Selections 1 and 3 were significantly more resistant to infection, far less adult worms being found in these. Resistance to a 3rd and final infection of the parasite was amplified appreciably in all groups but, again, the high-responder mice were significantly more resistant than the low responders. These results imply that host antibodies play an essential role in immunity to this parasite and that resistance cannot be attributed solely to non-specific macrophage activity or cell-mediated immune reactions, since the latter are equivalent in high and low lines and the macrophages of the Ab/L line of Selection 1 are hyperactive.

I feel greatly honoured to have been asked to speak to you about Alphonse Laveran. Professor Garnham wondered if I had met Laveran and what was the State of his relations with Professor Emile Brumpt my father. I have known many Pastorians: Emile Roux, Mesnil, Marchoux, Roubaud, Charles Nicolle, but unfortunately not Laveran.

A rapid method is described for preparing and staining salivary glands of Rhipicephalus appendiculatus ticks infected with Theileria parva. The technique, involving the use of a modified methyl green pyronin stain, minimizes the risk of losing material and allows examination of stained glands within minutes of preparation. The technique was applied in a series of studies in which ticks were either infected with T. parva under different conditions, or maturation of parasites in adult ticks was stimulated by different means. When nymphal ticks were fed on the ears of cattle the subsequent infection rate of the adult ticks showed no correlation with the parasitaemia of the cattle at the time of nymphal engorgement. There was no difference in infection rates between adult ticks in which parasite maturation had been stimulated either by incubation at 37 °C or by feeding on rabbits. However, parasite maturation took about 1 day longer in incubated ticks than in rabbit-fed ticks. Female ticks were consistently more highly infected than males, both in terms of the percentage of ticks infected and the mean number of infected acini/tick. Ticks were infected with T. parva by injection of nymphs with parasitaemic bovine blood, but the resultant adult infection was lower than that in ticks which had been infected naturally by feeding on cattle.

Parasitologists are fond of alluding to the possible antiquity of their chosen group. They may even place the origin in a specific period of geological time and trace its co-evolution, or lack thereof, with the hosts. These speculations usually make only passing comments on the actual fossil record, but a critical examination suggests that this area can throw much light on both the origins and evolution of parasitism. This review is concerned primarily with the fossil record and its immediate implications. It does not appraise parasite evolution in the light of evidence from sources, often of excellent quality, such as comparative anatomy and physiology or ecology. As some parasitologists may not be entirely familiar with the geological column and time scale, Table 1 depicts these and indicates some records of parasitism mentioned here, together with the major events in this history of life.