Toxocara genettae sp.nov. and Toxocara sprenti sp.nov. from viverrid hosts in Africa and S.E. Asia respectively are described. Seven Toxocara spp. from viverrid hosts are differentiated. The writer proposes that Toxocara canarisi Puylaert, 1967, from a feline host, become a species inquirendae requiring further study.

Plasmodium vinckei chabaudi (which has a 24 h cycle with high synchronicity) has a peak of schizogony in the early morning at about 02.00–04.00. This cycle is orientated to the cycle of the host (mouse or thamnomys). The male gametocytes become ripe for exflagellation in a well-marked wave from 22.00 to 08.00 with peak about 00.00–04.00. This timing presumably corresponds to the hours when the vector mosquitoes are most likely to suck blood, and it is adapted to facilitate transmission. The male gametocytes remain ripe for exflagellation for a mean period of about 6 h and then apparently degenerate.

A 37-spined Egyptian echinostome, Echinostoma liei sp.nov., is described in adult and larval stages. The parasite develops readily in the laboratory in chicks and ducklings, hamsters and rats. Its natural final host in or near irrigation ditches of the Nile delta involves the roof rat, Egyptian giant shrew and aquatic bird hosts. Developmental forms are described from infection of the NIH strain of Biomphalaria glabrata in the laboratory. B. alexandrina, is infected in the normal habitat in Egypt and contains both developmental stages in the heart or aorta and the hepatopancreas, and metacercariae encyst in the pericardium and kidney. E. liei sp.nov. is one of six very similar species characterized by 37 collar spines with a pattern of (3 + 2) corner spines in each lappet, six laterals on each side, and 15 dorsals in alternating rows; two pairs of dorsoventral and one small pair of ventro-lateral finfolds on the cercarial tail; and rodlike cystogenous material filling the cercarial encystation glands. In addition to distinctive intermediate-host specificity, differentiating characteristics of E. liei cercariae include presence of six sets of three flame cells each per side (total 36), seven oesophageal cells, eight penetration gland outlets on the dorsal lip of the oral sucker, and an absence of paraoesophageal gland cells as determined by intravital dyes. Significance of these and other cercarial traits is emphasized to aid in defining highly similar, but none the less distinct, sibling species.

Echinostoma liei, a newly described 37-spined eehinostome from Egypt, was tested against two trematodes in paired infections in the snail host, Biomphalaria glabrata (NIH strain). E. liei, when matched with the highly predacious Brazilian echinostome Paryphostomum segregatum, was dominated by the latter's predatory rediae. Pre-existing E. liei infections were destroyed, although the P. segregatum infection was itself delayed in development by an unidentified ‘indirect antagonism’ elicited by the E. liei larvae. In concurrent exposures with the two species, or with E. liei challenge of an established P. segregatum infection, the E. liei miracidia penetrated the snail, but the infection did not become established. When E. liei and S. mansoni were paired, the former species dominated. Exposure of snails already infected with E. liei to miracidia of S. mansoni slowed growth of the latter and the schistosome sporocysts eventually disintegrated without producing cercariae. When E. liei miracidia were exposed to snails with S. mansoni infections of different ages, the echinostome became established but developed slowly. Subsequently, however, it destroyed the schistosome infection. Although E. liei is itself quickly eliminated by P. segregatum, the two species appear almost equal in anti-schistosome capacity. This can be credited in part to a deleterious or lethal effect of the E. liei-schistosome combination on the host snail, as well as to a direct anti-schistosomal effect. Greater knowledge of this host-inter-trematode balance may permit the use of trematodes to attack infected snails and their parasites in regions hyperendemic with human schistosomiasis.

The effect of host age on the course of infection of Raillietina cesticillus in the chicken has been investigated. It was found that male hosts become resistant to the cestode with increasing age. This resistance manifests itself in an increased rate of destrobilization and consequent loss of scolices and in a decreased rate of growth of the worms. The cestodes are distributed over a greater length of intestine in old than in young birds. In female hosts age resistance develops more rapidly than in males until the birds are 84 days old and from this age onwards the manifestations of resistance decline. The possible factors responsible for age resistance to R. cesticillus are discussed.

The course of infection of Raillietina cesticllus in the chicken has been studied and information is presented on proglottid output, the dynamics of infection and the distribution and growth of the cestode. A posterior migration of young cestodes during the first 7 days of infection was confirmed and a progressive destrobilization of the worms was observed with complete destrobilization occurring 70 days after infection. No regeneration of strobilae occurs and the scolices are eventually eliminated. A marked difference in the rate of destrobilization in the two host sexes was noted.

A trypanosome identified as Trypanosoma (Schizotrypanum) dionisii Bettencourt & França, 1905, has been isolated from Pipistrellus pipistrellus (Chiroptera) in England. At least five out of eight P. pipistrelhis were infected. 2. In the blood of P. pipistrelhis, the parasite closely resembled T. (S.) cruzi. When grown in vitro in monophasic or diphasic media at 28°C, epimastigotes and trypomastigotes developed. The latter were of two types — very long, thin forms and less numerous shorter individuals. 3. The trypanosomes multiplied as amastigotes within HeLa and mouse L cells in vitro. After 6–9 days in HeLa cells at 37°C, they transformed into small trypomastigotes and emerged from the cells. Higher infection rates (up to about 4%) were obtained in cell cultures inoculated with flagellates from older monophasic cultures, which contained more of the long, slender trypomastigotes. 4. Trypanosomes also entered (or were phagocytosed by) up to 60% or more of mouse peritoneal macrophages in vitro. Multiplication occurred by binary and multiple fission of amastigotes in at least some of the parasitized macrophages and transformation into trypomastigotes was seen after 7 or more days at 37°C. Development in macrophages was less synchronous than in HeLa cells.

When ring-stage parasites are grown to the late trophozoite stage in vitro, the incorporation of [3H]adenosine into parasite DNA and RNA is in the ratio of ~ 1:1·5 and not 1:4 as expected from direct biochemical analysis of the parasite. A method is described by which large quantities of infected blood can be grown in vitro from the ring to the trophozoite stage thus allowing direct biochemical analysis of parasites grown in vitro. The results of direct biochemical analysis indicated that parasites grown in vitro have similar DNA and protein contents to those grown in vitro but that RNA contents are much less in vitro. Quantitative histochemical studies also indicated a deficiency in RNA in parasites grown in vitro. It is concluded from the evidence of three distinct methods that RNA synthesis is defective during the first asexual cycle in vitro. In the second cycle all three macromolecular biosyntheses studied are reduced when compared to the first so that the actual rate of RNA synthesis is further reduced when compared to that in vitro. It is suggested that the successive decrease in RNA synthesis parallels the reduction in multiplication obtained on subculture of the parasite.

Chicks hatched from eggs laid in the third and fourth weeks after inoculation of the hens with oocysts of E. maxima excreted fewer oocysts in response to a challenge inoculum of E. maxima given at 1 week of age than controls hatched from the eggs of uninfected hens. A λ-livetin fraction prepared from the yolks of eggs laid by hens 14–22 days after a single inoculation of oocysts of E. maxima and injected subcutaneously into 2-week-old chicks caused a similar reduction in oocyst yield from a challenge inoculum. The serum of the donor hens, obtained at the corresponding time intervals was protective. These results confirm that immunity to infection with E. maxima is, at least in part, mediated by humoral antibodies.

Goldfish were experimentally infected with different population densities of the acanthocephalan Pomphorhynchus laevis, and maintained at different temperatures. The density of infection had no effect upon the establishment of the parasite, but a 12°C rise in water temperature reduced the recovery after one week by 30%. Thereafter there was a continuous loss of parasites during the course of infection. The rate of this loss was independent of worm burden and temperature, but increased under conditions of host starvation. Both male and female parasites attached themselves in the same region of the alimentary tract, with a mean position about 19% along its length. They remained in that region throughout the course of infection, and the population did not migrate down the intestine with increasing age. In starved fish, the region of attachment was nearer the oesophagus, at low temperatures nearer the rectum, and when crowded the occupied region extended anteriorly. Male worms were unable to establish as easily as females, but once established survived better, and the sex ratio after two weeks was in favour of males. The results are compared with the results of studies on other acanthocephalans and on fish-cestode systems. It is recognized that although the establishment of fish acanthocephala is affected by temperature to a lesser extent than that of some fish cestodes, temperature in conjunction with changes in fish diet is a major control upon the flow of parasites through acanthocephalan-fish parasite systems. The significance of the results to the interpretation of data based on field observations is discussed.

The immune reaction of larvae of O. caesarion against the nematode H. autumnalis is characterized by melanization of the cuticle of the parasite and the accumulation and fusion of host haemocytes to form a homogeneous, multinucleated capsule around the parasite. The immune reaction is manifested as a change in the haemocyte picture of the host long before there is any visible evidence of melanization and encapsulation. Differential haemocyte counts from host larvae at various stages of infection showed a decrease in the number of oenocytoids. These data, together with histological studies, indicate that oenocytoids play an important role in the melanization and encapsulation of the nematode. The apparent increase in the number of circulating haemocytes in parasitized larvae suggests that the haemocytes are stimulated to move out of areas where they are normally located and to react against the parasite.

Ultrastructural observations on Moniliformis dubius, combined with measurements of envelope volume and composition at various stages during the parasite's development, suggest that production of envelope material is essentially complete by the stage at which elevation occurs. Elevation is associated with the production of an inner layer. In vitro observations on acanthors show that membranous coat material can be produced in the absence of haemocytes.

The structure of the various stages of Eimeria tenella grown in the chorioallantoic membranes of the chick embryo has been shown to be similar to the stages in the caecum of the bird. The effects of the anticoccidial drug, Robenidine, on the fine structure of the various stages of E. tenella, grown in the chick embryo and in the caecum of the bird, have been described. The first noticeable change occurs in the endoplasmic reticulum, including the nuclear envelope, and in the Golgi complexes of all stages. The nucleus itself, and the mitochondria, do not appear to be affected by the drug until much later, and this effect is probably due to the degeneration of the cell. It is suggested that the drug may have a direct effect upon protein metabolism of the parasite, resulting in swelling of the granular endoplasmic reticulum and Golgi complexes, or that it may have a primary effect upon some other organelle or metabolic process, and that the swelling of the endoplasmic reticulum and Golgi complexes is a secondary or tertiary phenomenon.

The ultrastructural morphology of selected microfilariae from four genera is described and compared. 1. The sheath is composed of a thick layer of material not limited by membranes. 2. The cuticle is composed of a trilaminate membrane, a dense cortical layer and an inner fibrous layer. The outer leaflet of the trilaminate membrane is covered with a dense surface layer. 3. The hypodermis is formed of four components, and the outer membrane of each component is castellated. 4. Muscle cells are located in the four quadrants of the worm; each cell is divided into a contractile and a non-contractile region. Anterior muscle cells are probably involved in the movement of the hook. 5. A buccal capsule is situated at the anterior tip of the microfilaria; it is connected to the pharyngeal thead. The thread is already surrounded by the future oesophageal cells. It is not yet known whether these structures are functional in the microfilaria. 6. Three kinds of sensory organelle have been identified; they all contain modified cilia. The hook is associated with one of the amphids. 7. The excretory vesicle opens through a pore in the cuticle and is surrounded at its base by an elongate cell. The apparatus may possibly have an excretory, secretory or osmoregulatory function. 8. The inner body is composed of dense, granular material; it is already surrounded by the future intestinal cells. The inner body is thought to represent some kind of reserve material. 9. Apart from its size the G1 cell shows no unusual characteristics. 10. The anal vesicle opens through a pore in the cuticle and is surrounded at its base by the three R cells. The anal apparatus may be instrumental in the removal of waste materials, or it may be involved in some secretory activity.

The relationship between changes in the temperature of storage of infective O. cuniculi larvae and the proportion that become inhibited in a subsequentinfection was studied. Prolonged storage at 5°C resulted in an initial inhibitionfollowed by acclimation to this temperature and subsequent normal developmentin the host. After acclimation to low temperature raising the temperature ofstorage produced no appreciable increase in the proportion of worms inhibited atthe early 4th stage. Maintenance of infective larvae at 15°C followed by a suddendecrease in storage temperature to 5°C resulted in rapid onset of inhibition. This inhibition was not reversed even after 25 days at the lower temperature. These temperature variations and the consequent pattern of arrested development werecompared to seasonal changes of spring and autumn occurring to nematode larvaeon pasture. An increase in the number of larvae given from 5000 to 15000 perrabbit had a slightly significant effect upon the proportion that remained inhibited. The need for careful assessment of the methods used for determining the extentof such inhibition is discussed.

A simple semi-mechanical sieving apparatus is described which rapidly concentrates helminth eggs from relatively large volumes of faeces. Tests showed the percentage recoveries of N. battus eggs after sieving 500, 750 and 1000 ml of diluted ovine faeces were 94·1, 88·1 and 84·8 respectively; for T. suis, Oesophagostomum spp. and H. rubidus eggs from 1000 ml. of porcine faeces, the percentage recovery was 94·8 for T. suis and 94·7 for the latter two worms. T. trichuira eggs have also been separated from human faeces using this apparatus.

An unusual new species of bopyrid parasite is described: unlike other bopyrids, the new species is attached on the dorsal surface of the abdomen of its host, a pontoniinid shrimp Periclimenes hertwigi Balss. A new genus has been erected for the parasite, Filophryxus dorsalis. It is distinguished from other genera by the presence of pereiopods I and II on the longer side of the body and pereiopods I, IV-VI on the shorter side, by three pairs of uniramous pleopods and no uropods on the abdomen. The specimen was collected off the Coast of Queensland, Australia, at a depth of 275 m.

Among the functional changes observed in L. truncatula infected with F. hepatica were those of growth, reproduction and mortality. For the first 3 weeks after infection there was no difference between the growth of infected and uninfected groups of snails. Thereafter there was a temporary accelerated growth which occurred between the fourth and seventh weeks after infection. The onset of this period of rapid growth in the different age groups of infected snails coincided with the time of migration of the rediae into the hepatopancreas. Of more significance was the influence of infection on the reproduction of the snail. There was a sharp decline in oviposition 2–3 weeks after infection, followed by a complete cessation of egg production at the end of the fifth week. Once oviposition ceased, it was not resumed and there was no self-cure. Contrary to general belief, infected groups of L. truncatula have been found to live longer than the uninfected controls. With isolated snails, however, there was a tendency for the uninfected snails to live longer than the infected ones. The possible interpretation of the discrepancies between isolated and mass cultured snails are discussed. The hepatopancreas and the gonad (ovotestis) were the two structures directly affected by the infection. Establishment of the rediae in the hepatopancreas invariably resulted in parasitic castration.