Fourth-stage larvae of Ascaris suum, recovered from piglets at 11–22 days post-infection (p.i.), were examined by light microscopy for changes in the somatic musculature. During this time the estimated total number of muscle cells in the body increases from approximately 600 to 21 000 cells. This non-eutelic development appears to occur by division of platymyarian muscle cells into coelomyarian cells, thereby increasing the number of muscle cells/quadrant from 5 to 85. The incompleteness of these divisions results in sarcoplasmic connections among muscle cells, and between muscle cells and nerve chords. At 11 days p.i., immediately after the 3rd moult, the variation in muscle cell length in a quadrant, with the longest cells being at the lateral chords, has been established. The average muscle cell length at this point is 0·101 mm, the longest is 0·164 mm. These values have increased to 0·365 mm and 1·122 mm, respectively, by 22 days p.i. At 18 days p.i. those cells in the posterior section of the larva are still the shortest in the body.

The choniostomatids parasitic on Crustacea have been exhaustively studied by Hansen. To the six genera and forty-three species he had described in 1897, he added a new genus and three more species in 1904, and seven more species in 1923. Scott (1904, 1905, 1907) described seven more species, Fraenkel (1915) three new species, Monod (1930) one, and Blake (1929) two. In 1929, however, Connolly described a new genus Choniosphaera and its type species C. cancrorum, from parasites found on American crabs Cancer amoenas, C. irroratus and C. borealis. In the present paper a new species Choniosphaera indica, parasitic on the edible crab Neptunus sanguinolentus of Madras, is described.

The effects of parasitization by Hyposoter exiguae on the nutritional physiology of Trichoplusia ni were influenced by the dietary sucrose level. The results confirmed that host nutrition plays a significant role in the manifestation of parasitic infection during the insect parasite-host association. Increased dietary sucrose level resulted in an increase in haemolymph trehalose concentration in both control and parasitized insects, but the increase was greater in the latter group. However, when the sucrose level was increased without energetic compensation and the dietary casein level was maintained constant, the haemolymph trehalose concentration was affected very little in unparasitized individuals but was markedly elevated in parasitized hosts. This result suggests that the de novo synthesis of carbohydrate in parasitized T. ni may not be regulated by dietary sugar intake.

Male and female congenitally athymic nude (nu/nu) mice infected with a single cysticercoid of Hymenolepis diminuta at 6 weeks of age retain the infection for at least 33 days. In the males of their phenotypically normal litter-mates, however, a single cysticercoid infection establishes and grows but is expelled between days 11 and 17. The unresponsiveness of the nude mouse to single H. diminuta infection is evidence that the immune rejection from normal mice is thymus-dependent.

It is probably a truism to say that what seems to be a single organism is, in fact, an assemblage of organisms – for there can hardly be an individual living outside a specialized laboratory that does not have commensals or parasites living within. The insects, the most diverse and numerous group of organisms on earth are no exception, and with micro- and macro-parasites from a wide range of taxa generate a remarkable range of interspecific associations. In some cases the insect is the sole host, in others it is an intermediate host or vector. It is the latter relationship which attracts much attention when insects and arachnids transmit infectious agents to humans, their animals or crops. Knowledge of the parasites of insects provides us with an opportunity to develop novel control methods for pests. Despite the diverse and widespread nature of insect infections, their impact on human well-being and the opportunity they give us to understand the complexity of the natural world, the subject remains a surprisingly neglected field. In this volume we endeavour to draw the veil from the 'black-box' approach to the insect stages of parasite life cycles to reveal some of the complexities of these relationships and how they are currently being analysed.

The parasitic worm fauna of domesticated animals in India has in the past been greatly neglected as a subject for research by zoologists working in that country. The increased interest in Helminthology during the last few years has been world-wide, and has led to greater attention being paid to Indian parasitic worms, such attention has, however, been largely devoted to the Roundworms, the Flatworms, with the exception of the Trematodes, receiving but scant attention.

The capillariid nematodes present in passeriform hosts collected in Taiwan are recorded and described. Two new species are established, Capillaria parusi sp.n. from Parus monticolus insperatus and Sitta europaea formosana, and C. madseni sp.n. from Corvus macrorhynchus colonorum, and their affinities are discussed. Capillaria tridens, C. longifila and C. contorta are recorded from a number of new hosts.

After 24 h desiccation at 28–29 °C and approximately 50 % relative humidity about 70 % of B. microplus larvae drank sufficient solution containing 1·5 mCi of 32P per ml for their movements on the host to be followed with a portable G-M counter. Reduced viability of the labelled ticks could not be detected when they were kept for 24 h on the host and either allowed to feed or prevented from doing so. When feeding was continued for 72 h or when larvae were incubated for 3–4 weeks, adverse effects were found, the severity of which could not be directly related to the amount of 32P label. Desiccation, handling of larvae and exposure to radiation in the drinking solution may have contributed to their reduced viability.

Since resistance to the tick is manifest within the first 24 h after infestation labelled larvae could be used to compare development on different hosts during this time. Even after feeding for 72 h, larvae were more adversely affected by host resistance than by labelling damage.

We would like to thank Mr C. A. Schuntner for helpful advice and Mrs J.Galligan for technical assistance. The financial support of the Australian Meat Research Committee is gratefully acknowledged. Messrs D. Hancox and S. R.Henderson assisted with some of the experiments.

Ultrastructural changes associated with exsheathment of the infective juveniles of Haemonchus contortus are described. Hyaline ring formation occurs associated with annulations 10 and 20 and consists of the dissolution of the basal zone and the inner electron-dense layer resulting in the rupture of the sheath. These changes are consistent with the action of a protease-exsheathing enzyme. There is a significant reduction associated with exsheathment in the size of the excretory cells and the number of excretory granules contained within them. No changes in the oesophagus were observed associated with exsheathment. These, and the observations of earlier workers, suggest that it is the excretory cells and not the oesophagus which are the source of exsheathing fluid during exsheathment.

The daily rate at which a young lamb acquired keds from its mother was studied. Keds applied themselves closely to the skin of the lamb, many on the under, sheltered parts of the body. It is concluded that there was almost completely oneway traffic of keds from the ewe to the lamb. A fall in the rate of transfer of keds to the lamb was attributed to declining frequency of contact between the latter and its mother, associated with transition from a wholly milk diet to one in which pasture became of increasing importance. It was found that during the hours of darkness and some hours of daylight few, if any, keds were acquired by the lamb. Keds tended to accumulate on the lamb in greater numbers during periods of many hours of bright sunshine and little rain than those of few hours of sunshine and much rain. The running totals of keds acquired by the lamb more nearly paralleled the running totals of hours of bright sunshine than other meteorological factors. It is concluded that the connexion was indirect and that sunshine raised the temperature of the fleece of the mother in the regions directly exposed to the rays, causing greater numbers of keds to appear on the surface, so that the lamb was exposed to a risk of heavier infestation. At one stage of the experiment a greater proportion of the males than females transferred from the ewe to the lamb. This is explained in terms of there being a higher proportion of males in the hinder part of the body of the ewe, a region with which the lamb, in feeding, came more frequently into contact. The higher ratio of males to females in the posterior half of the lamb than in the anterior is explained by the more pronounced habit of males than females to migrate through the fleece.

The rich material of Ixodoidea in our Museum, which I have recently studied, enables me to give records of the geographical distribution of some genera. The genus Dermacentor of the vast Russian territory, as I have shown elsewhere, is represented by two widely distributed species, D. reticulatus and D. niveus. The collection contains specimens from the following localities.

In the autumn of 1917 the writer received several letters from Mr L. C. Peters describing his experiences with flies hibernating in a large and very old house, situated in a large park at Frampton, near Kirton, Boston, Lincolnshire. Mr Peters' attention was directed first to the matter towards the end of October. On removing the window sashes the frames were found “black with flies.” After fumigation a bucketful of dead flies was removed from a single window frame, and about six bucketfuls from other infested windows. Only one side of the house was affected, but on that side the flies were found in the window frames on all three stories. “Ladybirds” were also present in large numbers.

Hosts face mortality from parasitic and environmental stressors, but interactions of parasitism with other stressors are not well understood, particularly for long-lived hosts. We monitored survival of flour beetles (Tribolium confusum) in a longitudinal design incorporating cestode (Hymenolepis diminuta) infection, starvation and exposure to the pesticide diatomaceous earth (DE). We found that cestode cysticercoids exhibit increasing morphological damage and decreasing ability to excyst over time, but were never eliminated from the host. In the presence of even mild environmental stressors, host lifespan was reduced sufficiently that extensive degradation of cysticercoids was never realized. Median host lifespan was 200 days in the absence of stressors, and 3–197 days with parasitism, starvation and/or DE. Early survival of parasitized hosts was higher relative to controls in the presence of intermediate concentrations of DE, but reduced under all other conditions tested. Parasitism increased host mortality in the presence of other stressors at times when parasitism alone did not cause mortality, consistent with an interpretation of synergy. Environmental stressors modified the parasite numbers needed to reveal intensity-dependent host mortality, but only rarely masked intensity dependence. The longitudinal approach produced observations that would have been overlooked or misinterpreted if survival had only been monitored at a single time point.

We analysed data on the abundance and distribution of 26 species of mesostigmate mites with different feeding habits collected from bodies of small mammalian hosts in 2 geographical regions (West Siberia and Argentina). We tested whether prevalence of a mite can be reliably predicted from a simple epidemiological model that takes into account mean abundance and its variance. We theorized that the difference between prevalence predicted from the model and observed prevalence would be smallest in obligatory haematophagous mites, intermediate in facultatively haematophagous mites and greatest in non-haematophagous mites. We also theorized that prevalence of mites from the region with sharp seasonality (Siberia) would be predicted accurately only if host number would be taken into account. We found that the success of a simple epidemiological model to predict prevalence in mites was similar to that reported earlier for other ectoparasitic arthropods. Surprisingly, the model predicted prevalence of obligatory exclusively haematophagous mites less successfully than that of mites with other feeding habits. No difference in the model performance between mites occurring in the 2 geographical regions were found independent of whether the model took the number of hosts into account.

Seasonal life cycle of body cavity dwelling (BCD) Philometra ovata (Nematoda: Philometridae) has been reported in southern and central European countries, but its swim bladder dwelling (SBD) stage and northern populations have remained unstudied. In this study, we investigated the seasonal life cycle and infection ecology of P. ovata in both swim bladder and body cavity in the European minnow (Phoxinus phoxinus) in Finland. The larval P. ovata infected the swim bladder of minnows mainly in August. Female SBD P. ovata emigrated to body cavity mostly in September, grew to their full size by the end of the next June, and evacuated from minnows in July. In addition, female SBD P. ovata retarding their development and staying in swim bladder were found commonly in minnows, thus the mean monthly prevalence (6·7 ± 3·9%) and mean intensity (1·4 ± 0·8) of BCD P. ovata was lower than that of SBD P. ovata (37·8 ± 15·1% and 2·0 ± 1·5, respectively). Finally, despite the large size of BCD individuals, infection of P. ovata did not impair body condition and relative gonad size of minnows, but increased the mortality and caused physical damages in their hosts during the evacuation period.

Extraordinary as any of the Mallophaga are when compared with conventional insect forms, there are some species of the order which are still more peculiar than the majority of their fellows. Among these unusually strange forms is that here to be dealt with, a species that seems to combine within itself the characteristics of two otherwise trenchantly separated groups, that possesses striking specific peculiarities and that in addition is decidedly aberrant in its choice of host. It has but once been recorded. The availability of further specimens makes possible additions to our knowledge of its structure and a reconsideration of its relationships.