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 sensory organelles and some components of the nervous system of the adult filarial worm Dipetalonema viteae have been studied by means of electron microscopy.The sensory organelles contain modified cilia innervated by nerve axons. The cilia lie within cuticle-lined channels. The amphids each contain nine such cilia, but the phasmids and the papillae contain only one cilium. The amphidial and phasmidial cilia are exposed to the external environment and it is suggested that I they function as chemoreceptors. The cilia within the cephalic and caudal papillae are modified so as to produce a greater area of sensitivity. The ciliary channels in the cephalic papillae do not open to the exterior and these papillae therefore probably function as mechanoreceptors. The caudal papillae of the male worm are structurally similar to the cephalic papillae, except that the ciliary channels are open to the external environment. It is suggested that these papillae function both as mechanoreceptors and chemoreceptors. The terminal pair of caudal papillae differ from all the other papillae. The ciliary channels of all the sensory organelles are surrounded by supporting cells, but multivesicular cells are only associated K with the amphids, phasmids and cephalic papillae.The nerve-ring encircles the muscular region of the oesophagus; it is composed entirely of nerve axons. The nerve axons contain two kinds of vesicle. The nervering is surrounded by an ensheathing cell. The major nerve bundles are carried by the hypodermal cords, but they are not embedded in the hypodermal cytoplasm. The nerve axons at the surface of the cord form synapses with the innervation processes of the somatic muscle cells.Electron cytochemical techniques have been used to investigate the distribution of cholinesterases in the structures described. Acetylcholinesterase has been identified in the amphids, phasmids, cephalic papillae and nerve-ring; it is suggested that acetylcholine functions as a chemical transmitter at these sites. Pseudocholinesterase has been identified in the amphids, phasmids and cephalic papillae, but not the nerve-ring; it is present in considerably smaller quantities than acetylcholinesterase.

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.

Six species of South African parasitic copepods belonging to the family Chondracanthidae were restudied. A redescription was given of Acanthochondria lepidionis, Ghondracanthus colligens and Ch. neali. Ch. lophii reported by Barnard (1955a) is actually a new species; it was named Ch. barnardi and redescribed. Ch. congiopodi Barnard, 1955, is conspecific with Ch. tuberculatus Nordmann, 1832. A redescription of this species was given based on Barnard's collection. Ch. merluccii was only mentioned and not redescribed.

A technique is described for obtaining consistent reinvasion and multiplication of the erythrocytic stages of Plasmodium falciparum from humans in vitro. Subsequent to this, P. falciparum was subcultured through almost three cycles in vitro, during which multiplication of the parasite was obtained in the first but maintenance or only slight increase in numbers was obtained in the second subculture. The effect of sera from adult Gambians on the reinvasion of P. falciparum was measured in vitro both morphologically and by the incorporation of [14C]isoleucine into parasite protein and by the incorporation of [3H]adenosine into parasite DNA and RNA. Two sera reduced the amount of reinvasion.

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.

The ultrastructure of the body wall of the redia of Sphaeridiotrema globulus is described. The tegument, which possesses numerous microvilli, is shown to be a syncytial, cytoplasmic layer connected to underlying subtegumentary ‘cells’ by cytoplasmic processes. Between the subtegumentary ‘cells’ are located the normal parenchyma cells of the body wall, which are believed to be important in carbohydrate storage.Mitochondria, Golgi complexes, endoplasmic reticulum and beta glycogen granules are located in the tegument and subtegumentary ‘cells’. In addition, large whorled bodies and dense secretory granules appear to be formed within the subtegumentary ‘cells’ prior to their passage into the outer tegument. It is suggested that these whorled structures are contributing to the growth of the tegument. Small membrane-bound ‘vesicles’ are also seen in the tegument and some of these may be pinocytotic in nature.Following incubation, horseradish peroxidase tracer was localized within ‘vesicles’ in both the tegument, subtegumentary ‘cells’ and parenchyma cells, which indicates that the redial body wall may be important in the uptake of nutrients.Phosphatase enzymes are abundant within the tegument, particularly in association with the plasma membranes and microvilli. These enzymes, which appear to have their origin in the endoplasmic reticulum of subtegumentary cells, are believed to be associated with the uptake of nutrients through the redial tegument.

No external signs of activation of cystacanths in the alimentary tract were observed until 25 min after oral ingestion. Peak percentage evagination was observed after 60 min.Activation and establishment of cystacanths were never found in the ventriculus or anterior to it, but several crushed specimens were found in the ventriculus, which is a mechanical hazard to the parasite.Infections established by cannulation at the yolk-stalk are greater than infections produced by ingested parasites; thus the ventricular environment does not need to be experienced by the freed cystacanth for activation to take place.

A comparison was made of the immunogenicity of normal worms, derived from a primary infection, and immune-adapted worms, derived from a trickle infection, after surgical transfer into previously uninfected rats. Exposure to 300 normal worms for 2 days was sufficient to induce resistance to challenge infection 3 weeks later in four of eight rats. The immune-adapted worms were, however, significantly less immunogenic, only one rat in ten developing resistance to challenge after 21 days exposure to 300 worms.These results offer further evidence that the protective antigens produced by normal worms are in some way altered in adapted worms, so that adapted worms have a reduced immunogenicity.

The initial pattern of oogenesis after a feed is similar for mated and unmated A. persicus. The peak number of mature oocytes within the females occurred on the seventh day at 30 °C. Both groups ovulated but only mated females oviposited.At the end of the first week the mature eggs of unmated females began to undergo dissociation and resorption. The early onset of this process seems to exclude the presence of unlaid eggs as a factor inhibiting ovarian maturation.Many more eggs matured within the mated than the unmated female. After oviposition, the ovaries appear as in the unfed virgin except oocytes are fewer.When the male was mated consecutively to the 7–8th virgin female, there was a decrease in the number of eggs laid. This indicates that the male factor(s) effecting oogenesis and oviposition act on a quantitative rather than an ‘all or none’ basis.To determine whether a female was effectively mated, the ampulla must be checked for sperm. The reason for this is that the spermiophore capsules may be resorbed or may lack sperm.Spermless spermiophores enhanced fecundity but did not effect oviposition.There was evidence of mechanical influence on oocyte maturation when beads were introduced into the vagina of A. persicus. An increase in the number of beads increased the number of mature oocytes.Chemical influence on oogenesis was demonstrated by injection of male gland complex into the body cavity of unmated females.

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.