Showing papers in "Parasitology in 1974"

The tegument of Schistosoma mansoni: observations on the formation, structure and composition of cytoplasmic inclusions in relation to tegument function.

Abstract: Two major cytoplasmic inclusions, multilaminate vesicles and discoid granules, are present in the tegument of Schistosoma mansoni. These are produced at separate Golgi apparatuses in the tegument cell bodies and move up to the surface by a combination of diffusion and fluid flow. The discoid granules contain neutral mucopolysaccharide and are believed to break down to form the ground substance of the tegument. The multilaminate vesicles are rich in phospholipid and the contents, at least superficially, resemble unit membranes. The multilaminate vesicles are believed to contribute their contents to the multilaminate surface of the worm which appears to be continually replaced. These observations are related to current ideas on membrane turnover and the ability of the worm to acquire a disguise of host erythrocyte glycolipid.

Inhibited development in Ostertagia ostertagi infections – a diapause phenomenon in a nematode

Abstract: Experiments are described which show that in a recently isolated field strain of the cattle nematode, Ostertagia ostertagi, the primary stimulus to the induction of inhibited development at the early fourth larval stage (EL4) in the host is chilling of the infective larvae (L3). Thus exposure of L3 to a temperature of 4 °C for 8 weeks prior to their oral administration to calves resulted in a mean of 66% of the established worm burden becoming inhibited at the EL4 stage. This provides an explanation for the seasonal occurrence in Britain of inhibited EL4 stages of O. ostertagi in cattle during the cold climate of late autumn and winter.If the L3 stages were exposed to chilling for a prolonged period (> 19 weeks), prior to infection of calves, then the prevalence of inhibited EL4 stages amongst the worms established declined. After 33 weeks chilling the worm population consisted almost entirely of adults and only 2% inhibited EL4 stages. This suggested that a selective mortality of inhibition prone L3 was taking place and explained why under natural grazing conditions inhibition prone L3 were not available on the pasture in spring.The duration of inhibition at the EL4 stage in calves infected with chilled L3 was consistently between 16 and 18 weeks and maturation of the majority of the inhibited larvae occurred spontaneously after such a period and irrespective of season. This period is equivalent to the duration of a normal winter in Britain when conditions unsuitable for the free living development of O. ostertagi larvae prevail.The induction of inhibition by the environmental stimulus of chilling, the fixed period for the duration of inhibition within the host and the spontaneous maturation of the inhibited larvae are characteristic of a true diapause.

An in vitro investigation of dynamic processes occurring in the schistosome tegument, using compounds known to disrupt secretory processes.

Abstract: The structure of the schistosome tegument can be changed by in vitro incubation of worms in medium containing chemicals selected for their ability to disrupt secretion in other cell systems. The observed structural changes support the hypothesis that the function of the discoid granules is to maintain the integrity of the tegument ground substance. They further support the idea that the multilaminate vesicles and/or their contents are incorporated into or on to the worm surface as part of a mechanism of surface turnover. Vesicle life appears to be similar to that estimated for other trematodes and in cestodes. In addition the worm surface appears to be replaced more rapidly than the worm acquires and loses its disguise of host antigens. It is suggested that the surface channels of the tegument may be a variable feature, and that transfer of fluids between environment and interstitial spaces may occur across the tegument.

Studies on the host specificity of the eyefluke, Diplostomum spathaceum, in brown and rainbow trout.

Abstract: Trout collected from the Hanningfield Trout Farm in Essex, England, were found to be infected with Diplostomum spathaceum. Yearling rainbow trout were blinded with heavy infections of eyefluke, whereas brown trout of the same age carried one-tenth the number of flukes and were clear eyed. Both species were reared under identical conditions, in parallel rearing channels which received water from a common source. Samples showed that young fish exhibited a similar differential in their infestations, and that rainbow trout did not appear to be age-resistant. Laboratory infections produced by exposure of fish to suspensions of cercariae and injection of cercariae into the body cavity reflected the field results, indicating that ecological factors were not involved. Recovery of cercariae from host tissues, and histological observations of similar numbers entering both hosts, indicated that cercariae were able to survive penetration. Excised eye preparations were equally susceptible to infection. Two cm fry of both species were shown to be highly susceptible. Migration in brown trout took 3 h longer than in rainbow trout of the same size, many cercariae being found in the heart during this time. Two mechanisms of insusceptibility were suggested: (1) a greater impenetrability of brown trout tissues; (2) a disorientation of migrating cercariae in brown trout.

Investigations into natural and experimental infections of freshwater fish by the common eye-fluke Diplostomum spathaceum Rud.

Abstract: The range of fish hosts parasitized by Diplostomum spathaceum was assessed. Natural and experimental levels of infection were compared between host species. The accumulation of eye flukes with age was established in one host – Rutilus rutilus. Development of metacarcariae in lenses of naturally infected Gasterosteus aculeatus throughout the year was compared with that of experimentally infected South African clawed toads, Xenopus laevis , maintained at various temperatures (5–30 °C). The importance of temperature changes to this part of the life-cycle of the parasite is discussed.

Humoral encapsulation in Diptera (Insecta): defence reactions of Chironomus larvae against fungi

Abstract: Humoral encapsulation is an effective defence reaction against fungal pathogens. The development of injected spores in the haemocoele of Chironomus larvae may be completely (Aspergillus niger) or partially (Mucor hiemalis) prevented by this reaction. The encapsulation proceeds very rapidly; within 5 min of injection most of the spores are enclosed in a solid capsule. Disintegrating blood cells may participate in the formation of capsule substance, but this is not usually the case. Encapsulation also occurs within the cuticle against invading hyphae of Beauveria bassiana. Histochemical tests show that the capsule substance does not consist of polysaccharides; some tests for proteins and all tests for melanin were positive. The significance of melanin formation and the biochemistry of the phenoloxidase system in insects is discussed in detail. The data presented lead to the conclusion that humoral encapsulation is based upon an activation of phenoloxidases and that the capsule substance represents a polyphenol—protein complex. In contrast to current opinion, the formation of melanin in cellular as well as in humoral encapsulation is not considered to be a secondary process, independent of the actual encapsulation procedure. Instead, the authors interpret the presence of melanin as an indication of the activity of phenoloxidases which cause the formation of a capsule substance on the surface of the parasites.

The effect of the acanthocephalan Pomphorhynchus laevis upon the respiration of its intermediate host, Gammarus pulex.

Abstract: The respiration rates of individual Gammarus pulex infected by larval Pomphorhynchus laevis were investigated with particular reference to the stage of development of the host and parasite and to the water temperature. At 20°C the oxygen consumption of Gammarus of all sizes was reduced by an average of 19·3 % by the presence of cystacanths of the parasite, but was unaffected by the presence of acanthellae. It is considered that the small size of this larval stage, in relation to that of its host, is responsible for the failure to detect an effect. Multiple infections did not exert any greater effect upon host respiration than single cystacanths, nor did it appear that the parasite had different effects upon hosts of different sexes. At 10°C no significant differences were observed between the respiration rates of infected and uninfected gammarids. The parasite was probably still depressing the host respiration rate at this temperature, but the oxygen uptake of G. pulex is so low that the differences between infected and uninfected individuals were too small to be detected. The parasite has a direct effect upon the physiological processes of the host, but neither the mechanism of this nor the reasons for the different effects found in different host-parasite systems are yet understood. Despite the pronounced effect of P. laevis on respiration of individual hosts, its effect upon the oxygen consumption of a natural host population is small since only a small proportion of the population carries infections and water temperatures remain below 10°C for over half the year.

Acquired immunity to Schistosoma mansoni in the rat: measurement of immunity by the lung recovery technique.

Abstract: Acquired immunity to Schistosoma mansoni in the rat can be assayed by the recovery of a proportion of the schistosomula of a challenge infection from the lungs 5 days after the challenge has been given. The recoveries from immune rats, which are significantly less than those from control animals, demonstrate that a proportion of a challenge infection is killed in the lungs or at an earlier point in the pathway of migration.Immunity in the Sprague–Dawley rat can first be shown by the lung recovery technique 3 weeks after an immunizing exposure of 500 cercariae. Immunity reaches a peak between weeks 6 and 7 but then declines to zero by week 12. The PVG inbred Hooded rat shows a similar but delayed development and decline of immunity. When the lung recovery technique shows immunity to be declining, hepatic perfusion demonstrates that immunity to reinfection is partially retained, indicating that at this stage the challenge is killed after the first 5 days.Re-exposure of rats in which immunity has declined induces an anamnestic lung recovery response. There appears to be a relationship between spontaneous cure and the decline of immunity. A factor in the serum of infected rats which kills young schistosomula in culture develops in parallel with immunity, but high titres of this factor are maintained during the decline of immunity.

The role of the foreign surface and female parasitoid secretions on the immune response of an insect

Abstract: Most successful parasitoids are able to avoid the encapsulation reaction of their host A similar avoidance was observed with particles of a weakly acidic cation exchanger which was not encapsulated following its injection into the haemocoele of an insect The ionic nature of the surface of the acidic cation exchanger and the two species of parasitoid eggs appeared to be similar A weakly basic anion exchanger was readily encapsulated following injections into the haemocoele of a host The encapsulation of the basic anion exchanger was prevented by coating the surface with fluid from the calyx region of the female parasitoid ovary The importance of the fluid from the calyx region of the parasitoid and the ionic nature of the surface in avoiding the encapsulation reaction of the hosts haemocytes is discussed

The life-cycle of Bucephaloides gracilescens (Rudolphi, 1819) Hopkins, 1954 (Digenea: Gasterostomata)

Abstract: The cercaria and sporocyst of Bucephaloides gracilescens are described from Abra alba (Wood). Observations were made on the behaviour of the cercaria and the mechanism of release from the first intermediate host. The metacercaria was obtained experimentally for the first time using Ciliata mustela (L.), a species of Gadidae from rock pools, as second intermediate host. It has not previously been recorded from this fish. Unsuccessful attempts were made to infect species of fishes from three other families, namely, Bothidae, Pleuronectidae and Gobiidae, confirming the high degree of host specificity of the metacercaria to Gadidae. The metacercaria, its development and effect on the host are briefly discussed. It was linked with the adult on the basis of comparative morphology and ecology of the hosts.

Parasitic protozoa of the blood of rodents: a revision of Plasmodium berghei.

Abstract: Lowland populations of the Plasmodium berghei group are compared with strains from the highlands of Katanga, Republic of Zaire, and it is concluded that the former warrant separate specific status. It is proposed that Plasmodium berghei yoelii of the Central African Republic be raised to a species, P. yoelii, and the lowland subspecies from the CAR, Brazzaville and Nigeria be moved to this species as P. y. yoelii, P. y. killicki and P. y. nigeriensis. P. berghei from Katanga would then revert to a monotypic species.Differences between P. berghei and P. yoelii are in distribution, hosts, optimum temperatures of sporogony, sizes of mature oocysts and of sporozoites, rates of growth and minimum maturation times of tissue schizonts in the liver of the white rat, the forms of six enzymes and the DNA.Differences between three subspecies of P. yoelii are in distribution, the sizes of mature oocysts and of sporozoites, sizes of tissue schizonts in the liver of the white rat, the effect of tissue forms on the nuclei of infected parenchymal cells and the electrophoretic forms of the enzyme GDH.

The population dynamics of Lepeophtheirus pectoralis (Müller): dispersion pattern.

Abstract: The numerical relationships between a population of Lepeophtheirus pectoralis and its host population (plaice) have been described. There was no significant difference between infection levels in male and female plaice. In most of the monthly samples (75%) there was no significant relationship between host length and either the incidence or intensity of infection. The samples in which significant positive correlations occurred were usually taken within the period November to April. It is probable that the immigration of smaller fish, with lower levels of infection, from shallower water produces this effect.The parasite population was found to have an overdispersed distribution (variance > mean) within its habitat, the host population. The frequency distributions of numbers of parasites per fish were calculated and the negative binomial distribution was fitted to these. The fit was good in 22 of the 24 samples and the value of k, the exponent, was found to be directly related to the mean density of the parasite population. Iwao's (1970) method of dispersion analysis indicated that the observed negative binomial was generated by a model of randomly distributed clumps or colonies of individuals. A possible mechanism of producing this pattern was proposed based on evidence from studies of mortality in the parasite population (which indicated that all-or-none type mortality operates on the clumps at certain periods during the year), the infection process (which demonstrated that a single wave of infection produces an overdispersed spatial distribution) and the examination of parasites from individual fish (which displayed a clumping of parasites at certain stages rather than an even spread over the range of possible stages). The mechanism proposed is that the adaptations for host location of the infective copepodid stage tend to produce aggregations of these larvae in favourable areas of a heterogeneous habitat. Fish moving randomly into these areas will tend to be infected by more than one larva (a clump of larvae) at any one time when available for infection. The fish can be regarded as equivalent to random samples of the free larval population and the aggregated distribution of the parasite population on its hosts is therefore directly related to the aggregated distribution of the free-swimming infective larvae.

Studies on the immunity of sheep to Oesophagostomum columbianum: effects of low-protein diet on resistance to infection and cellular reactions in the gut.

Abstract: Adult Oesophagostomum columbianum populations were larger in sheep fed low-protein diets than in adequately fed animals. Diet did not influence the numbers of larva which became established in sheep. Sheep fed high-protein diets eliminated more worms and were more immunologically competent than poorly fed animals. More encapsulated larvae, showing arrested development, were found in adequately fed sheep than in those fed low-protein diets. Adult O. columbianum produced eggs at an earlier time after infection in poorly fed sheep than worms in well fed sheep. More eggs/female worm were produced in sheep on a low-protein diet compared with the number of eggs produced in well fed hosts over the last week of the infection. The effects of immunity on the behaviour of the worm in both host diet groups is discussed.There was a greater cellular proliferation in the intestines of infected adequately fed sheep than in infected animals on low-protein diets. These changes were most pronounced in the large intestine where the adult parasites were found. The macrophage-lymphocyte series of cells underwent hyperplasia in well fed animals but these changes were reduced, particularly among the plasma cells, in sheep fed low-protein diets. Increased mucin and mast cell counts were observed in sheep on high-protein, but not in hosts on low-protein diets: the intestinal populations of eosinophil and globule leucocytes were also reduced in poorly fed sheep.The relationship of these various cellular reactions and their effect on the protective immunity of sheep to O. columbianum is discussed. It was concluded that the increased susceptibility of protein deprived sheep to O. columbianum infections was associated with malfunctions of the innate immunity of the gut, involving decreased peristalsis and failure of the mucin cell response, and with reduction of the adaptive immune response which was reflected by impoverished lymphocyte and plasma cell reactions, and possibly with poor cooperation between sensitized lymphocytes, antibodies and the mast cell-granulocyte effector mechanisms in protective immunity.

Host skin mucus as a hatching stimulant in Acanthocotyle lobianchi, a monogenean from the skin of Raja spp.

Abstract: When incubated at 13°C in alternating 12 h periods of light and darkness eggs of Acanthocotyle lobianchi rarely hatch. Hatching was not induced by shadowing or by mechanical disturbance. When skin mucus from the host ray was added to eggs which were more than 15 days old, hatching occurred almost immediately in about 60% of all eggs tested. Susceptibility to host mucus increased with the age of the eggs so that after 26–30 days of incubation over 80% of the eggs tested hatched. Some oncomiracidia were found to remain alive for up to 83 days in the egg, although they appeared to be fully developed at 15 days. Lipid droplets in the body of the 15-day-old oncomiracidia gradually disappeared as the eggs aged and it is suggested that these droplets serve as a food store for resting larvae.

The effects of fish skin mucus on hatching in the monogenean parasite Entobdella soleae from the skin of the common sole, Solea solea.

Abstract: Previously it has been shown that eggs of the skin-parasitic monogenean Entobdella soleae, maintained free of host contamination at constant temperature (12 °C) and exposed to alternating 12 h periods of light and darkness, hatch during the first few hours of each period of illumination as a result of endogenous processes in the larva in conjunction with the illumination cycle. Washings, prepared by immersing the parasite's host (the common sole, Solea solea) for 1 h in seawater (just sufficient to cover the body), enhance this ‘morning’ hatching. Furthermore, the application of host washings during the latter half of the period of illumination or during the dark period also stimulates hatching. Experiments have shown that the hatching factor is present in sole skin mucus, is not destroyed by boiling for 5 min or by freezing and is produced by small soles measuring 4–5 cm in length as well as by larger soles (15–21 cm long).When eggs are incubated at about 12°C in the absence of fish washings, hatching begins about 30 days after laying, but there is evidence that some of the larvae inside their shells are fully developed and capable of hatching in response to host hatching factor 1–3 days earlier.When fish washings are added to eggs which range in age from 25 to more than 30 days (at 12 °C) many eggs are stimulated to hatch (in addition to ‘morning’ hatching as a result of endogenous rhythmical processes and the illumination cycle) and others fail to hatch. These remaining unhatched eggs, in the absence of further treatment with host hatching factor, will complete their development and subsequently will hatch during the ‘morning’ hours in response to the illumination cycle. Further contact with host hatching factor is likely to stimulate the hatching of some of these remaining eggs.The host hatching factor is not specific to S. solea; washings from plaice, dab, halibut, whiting and ray induce hatching in E. soleae. In experiments in which oncomiracidia were offered scales from dab and sole, most of the attached larvae were found on sole skin, irrespective of whether the hatching stimulant had been provided by dab or by sole.The relationship between the behaviour of the common sole and hatching phenomena in the skin parasite is discussed; hatching rhythms and the use of host hatching factors adapt the parasite to take advantage of most opportunities to infect the host.

An histological and ultrastructural study of Thelohania contejeani Henneguy, 1892 (Nosematidae), Microsporidian parasite of the crayfish Austropotamobius pallipes Lereboullet

Abstract: An outbreak of the Microsporidian parasite Thelohania contejeani is reported in a population of Austropotamobius pallipes in Northumberland, U.K. Since less than 10% of all crayfish caught were infected it is concluded that T. contejeani has no serious effect on the population studied. The mode of transmission of the parasite from host to host is discussed.The host–parasite relationship and life-cycle of T. contejeani were studied using histological and electron microscope techniques. Spores were observed in some detail, and diplocarya, sporont and pansporoblast stages were identified within the general spore mass that invades host muscle tissue. Using serial sections the sporoblast ‘diplocaryon’ was shown to be a single nucleus with a deep cleft. T. contejeani was found to occur mainly in striated muscle, although it was found in cell bodies in the central nervous system.

Experimental infections with Trichostrongylus colubriformis (Giles, 1892) Loos, 1905 in lambs: worm burden, growth rate and host resistance resulting from prolonged escalating infections.

Abstract: Lambs were infected at daily intervals from 3 weeks of age with increasing doses of infective larvae of Trichostrongylus colubriformis , according to an exponential infection schedule designed to simulate the pattern of infection experienced by grazing lambs during the spring and early summer in Britain. The faecal egg counts and the worm burdens in the lambs followed a similar exponential trend for 12 weeks after initial infection. The T. colubriformis burdens in these lambs appeared to be cumulative during the first 12 weeks, after which the animals developed a resistance to further reinfection, which was very strong by 16 weeks after initial infection. However, even lambs which were refractory to new infection continued to harbour large numbers of adult worms, which caused clinical disease in most of the lambs. There was no evidence to suggest that either a turnover of the worm burden, inhibition of larval development or the sudden loss of established parasites played any major role in the regulation of the burdens of T. colubriformis in these young lambs. The removal of the established burden 16 weeks after initial infection in one lamb appeared to result in a partial loss of resistance to a challenge infection given 10 days later.

The functional significance of scolex retraction and subsequent cyst formation in the cysticercoid larva of Hymenolepis microstoma.

Abstract: The cysticercoid type of larval development, involving the retraction of the scolex and the associated development of a cyst, is of widespread occurrence within cyclophyllidean cestodes, but previously its possible adaptive value has been unexplained. Scolex retraction in Hymenolepis microstoma is an active, muscular process which takes only about a minute to complete. Following its retraction the scolex develops adult structures. The cyst enclosing the scolex also differentiates further, involving the secretion of three layers of collagen fibres and the development of a myelin-like layer adjacent to the retracted scolex. The cells within the cyst, including the muscle, become condensed or are autolysed causing a decrease in thickness of the cyst and an increase in the proportion of fibrous tissue. The collagenous part of the cyst provides mechanical protection for the scolex during grinding by the teeth on entry into the mouse host. The myelin-like layer insulates the scolex from the low pH conditions of the stomach. Values of lower than pH 3·0 are lethal to newly excysted worms. The myelin-like layer loses its insulatory capacity following exposure to bile salts.

Population dynamics of Hymenolepis nana in mice: fecundity and the ‘crowding effect’

Abstract: Young white mice were infected with different doses of eggs or cysticercoids of Hymenolepis nana and the subsequent faecal egg output was measured over a 3-day period. This was then correlated with worm numbers, determined after killing the hosts. The longest worm in each infection was measured and it was shown that crowding decreased the linear dimensions, number of eggs per proglottis and rate of proglottis production of these worms, but that their shape was not affected.The relation between total egg output and worm numbers was complex. In both egg-derived and cysticercoid-derived infections the egg production rose to a peak, fell and then levelled off to a constant rate with increasing worm numbers. Cysticercoid-derived worms were larger than egg-derived worms, but produced approximately the same number of eggs per unit of biomass. The differences in the egg output curves for the two types of infection were interpreted as being due to their size difference; this in turn may be a consequence of the host immunological response.

Further parasites of the family Garniidae (Coccidiida: Haemosporidiidea) in Brazilian lizards. Fallisia effusa gen.nov., sp.nov. and Fallisia modesta gen.nov., sp.nov.

Abstract: Fallisia effusa gen.nov., sp.nov. (Haemosporidiidea: Garniidae) is described in the teiid lizard, Neusticurus bicarinatus, from Para State, north Brazil. Schizogony and gametogony both take place within thrombocytes and white cells of the peripheral blood. There is no development in the red blood cells, by which character the organism is differentiated from Garnia, the other known genus within the family. Another species, Fallisia modesta gen.nov., sp.nov., is described in the iguanid lizard, Tropidurus torquatus hispidus, also from Para, Brazil. It is distinguished from F. effusa by its development principally in the lymphocytes, as opposed to the thrombocytes. There are other, striking morphological differences between the two species. It is recommended that great care is needed in the interpretation of so-called ‘exo-erythrocytic stages’ of saurian plasmodia, which may well really belong to members of the Garniidae, in mixed infections.

The specific immunoglobulin response in cattle immunized with isolated Theileria parva antigens.

Abstract: Cattle were inoculated with purified Theileria parva piroplasm and/or schizont antigen. Two similar inoculations were given 10 days apart. Serum samples were regularly collected and the indirect haemagglutination (IHA), indirect immunofluorescence (IFA), complement-fixation (CF) and immunodiffusion (ID) tests were used to detect T. parva antibodies. Selected sera were separated by Sephadex G 200 and fractions examined for specific immunoglobulin activity. With the IHA test specific antibody first appeared 4 days post inoculation (dpi) and reached high titres by 8 dpi. With the IFA and CF tests specific antibody also appeared 4 dpi and reached high titres by 8–14 and 10–14 dpi respectively. Specific ID activity was detected as early as 6 dpi and persisted for the length of the experiment. On fractionation of the sera both the IHA and CF tests indicated a sequential production of T. parva IgM and 7S Ig. However, in cattle inoculated with schizont antigen only, a significant 7S Ig component was not detected by the IHA test until 16 dpi, but was demonstrated by the CF test 7 dpi. The IFA test, however, detected anti T. parva activity almost exclusively in the 7S Ig fractions. All cattle were challenged 35–42 dpi with infective T. parva stabilate and all cattle proved fully susceptible. The lack of protection by high titres of specific T. parva immunoglobulin is discussed, together with the data on the differential immunoglobulin response, in relation to previous results.

Experiments on insemination in Moniliformis dubius (Acanthocephala).

Abstract: Some effects of insemination on Moniliformis dubius were studied by means of a surgical technique involving the transplantation of worms of known age, sex and reproductive state from one male rat to another. Insemination resulting in the development of eggs was found to have occurred in female M. dubius aged 16 days. An individual male M. dubius was found to be capable of inseminating as many as 17 females of the same age. The duration of the patent period appeared to be related to the length of the period of contact between male and female worms at the start of the course of infection. The evidence indicated that the patent period of a female worm was curtailed in cases where the female was isolated from males sooner than 5 weeks after the start of the infection. Male worms estimated to be not more than 21 days old were found to be capable of inseminating females older than 100 days; in these cases, the patent period was brief. Evidence was obtained to suggest that insemination is followed by further growth of the somatic tissues of the female worms. These results apply to experimental infections, and caution should be exercised in applying them directly to natural infections.

Intermittent egg release by Aspiculuris tetraptera in mice.

Abstract: In order to study egg release by Aspiculuris tetraptera total faecal collections from infected mice were made every 1½ h throughout successive 24 h periods. This was done with the aid of a histokinette machine. The cage containing the mice was suspended from one of the arms of the machine and every 1½ h the cage was moved on by the machine to the next adjacent collecting dish. The faecal pellets passed were counted and then used for flotation egg counts. It was found that eggs were not released steadily and continuously and, in the case of the worms in an isolated mouse, egg output was clearly intermittent. Egg production did not appear to vary with the faecal production of the host in a consistent way but with two groups of 8 mice it was highest when faecal production was at its peak shortly before dawn. For the groups of 8 mice the concentration of eggs per faecal pellet was also highest at this time. In two experiments with an individual mouse, however, the egg counts fell to zero at dawn before the level of faecal production became reduced. It is suggested therefore that egg output by female A. tetraptera may be stimulated by the altered physiological state of the host associated with feeding or general activity.