The cestode, Hymenolepis diminuta, and the acanthocephalan, Moniliformis dubius, were found, by Chandler (1939) and Burlingame & Chandler (1941) respectively, to undergo an anterior migration in the intestine of rats after the establishment of the infection. More recently, these results have been confirmed by Holmes (1961, 1962) who stated that it is not unlikely that the worms select optimum sites along one or more of the many gradients known or postulated to exist along the length of the small intestine.

A tissue phase of the nematode A. dissimilis has been demonstrated. The larvae enter the tissue soon after hatching and not, as previously thought, after 7 days.

The growth rate of A. dissimilis in young poults has been studied. Sexual differentiation can be observed from the 14th day and sexual maturity occurs as early as 28 days after infection.

From the recorded figures it is evident that A. dissimilis is not necessarily a smaller species than A. galli. The age of the host influences the development of maturity of the worms and probably the size of the nematodes as well. The largest female recorded here was 128 mm and the largest male was 77 mm when removed from a turkey 76 days after infection.

The infectivity of A. dissimilis ova is not impaired after storage at room temperature in 1 % formalin for up to 237 days. Embryonation is complete in 9–10 days at 30 °C.

It has been shown that chickens are probably refractory to A. dissimilis.

We wish to acknowledge the technical assistance of Mr J. Brownbill, Mrs B. Fisher and Mr P. R. Mills.

Laboratory infections of Polymorphus minutus in domestic ducks have been studied, and the parasites have been found to move posteriorly for a distance of about 4% of the host's intestinal length during the course of the infection.

No evidence has been found for male and female worms having different attachment zones.

Worms which had become attached anterior to a position 60% along the intestinal length were considered to be more likely to move or be expelled from the host before other worms in the population.

Growth of male and female worms was studied by weight measurements. The growth rates of worms of both sexes are similar during the first week of the infection, but by the third week the weight of female worms is more than twice that of male worms.

Mature eggs were first found in the host's faeces from 22 to 25 days after the beginning of the infection. Egg release continued for a variable period depending on the number of female worms present in the host.

The average peak rates of egg production were 1700, 2000 and 700 eggs/day/ worm for the three cases studied.

Eggs were estimated to remain for 50–100 min in the duck's intestine after being released by the worms but before being passed out of the host.

The introduction of a Perspex cannula into the small intestine of a domestic duck does not disturb the environment of P. minutus.

We are most grateful to Dr R. C. Campbell, School of Agriculture, University of Cambridge, for all his help and advice about the statistical analysis employed in this work, to Mr J. A. F. Fozzard, Department of Anatomy, for taking the radiograph, to Dr P. Tate for helpful discussions, and to the S.R.C. for a grant for P.J.W.

A series of observations on the feeding behaviour of a laboratory strain of Rhipicephalus appendiculatus on rabbits and measurements of the fluid consumption during feeding in vitro have been made.

Male and female ticks less than 5 weeks after moulting were less inclined to attach than older ticks.

Female ticks fed slowly during the early stages of attachment until after approximately 6 days of attachment when engorgement proceeded very rapidly and their body weight increased by approximately thirty times. Male ticks fed steadily until they roughly doubled their weight in approximately 7 days.

By an in vitro feeding technique in which whole blood, serum or plasma was offered in capillary tubes placed over the mouthparts, it was possible to measure the volumes absorbed over a period of 24 h. More serum or plasma was consumed than either defibrinated or heparinized blood. After 4 or 5 days’ attachment on a rabbit, females generally consumed greater volumes than males.

Dr G. H. Freeman, Head of the Statistics Division of the East African Agriculture and Forestry Organization, kindly carried out the statistical analysis of the quantitative data on the in vitro feeding.

Acknowledgements are also due to the technical staff who contributed to this work, especially to Mrs D. Backhurst. Mr K. P. Bailey maintained the colony of R. appendiculatus from which the ticks used in this study were derived.

This work was carried out during the assignment of one of us (L.P.J.) by the Food and Agriculture Organization of the United Nations to the East African Veterinary Research Organization.

Sections of salivary glands from the tick R. appendiculatus have been studied to obtain data on the incidence and development of Theileria parva during feeding. Adult ticks previously fed as nymphs on infected cattle were allowed to attach to rabbits after different periods following moulting and removed for dissection after different periods of attachment.

The maximum number of parasites was present from the 3rd to the 5th days of attachment when 30·5–42 % of salivary glands were infected. A small number of undeveloped parasites was observed in the salivary glands of unfed ticks.

The parasites were classified by their appearance into young, intermediate and mature forms and it was shown that the greatest numbers of mature forms were present on the 4th and 5th days of attachment.

It was concluded that with this strain of ticks, reared and infected under the described conditions, the most suitable time for the recovery of the infective forms of T. parva would be the 4th day of feeding.

Acknowledgements are due to the technical staff who contributed to this work, but especially to Mrs D. Backhurst who supervised the processing of the many sections, to Mr B. Wood who prepared the photomicrographs and to Mr K. P. Bailey who maintained the colony of infected R. appendiculatus.

This work was carried out during the assignment of one of us (L.P.J.) by the Food and Agricultural Organization of the United Nations to the East African Veterinary Research Organization.

The growth of an axenic strain of Entamoeba invadens in two media (Trypticase–liver broth and Trypticase–Panmede) is compared with that of a monobacterial strain in diphasic medium supplemented with starch. The axenic strain multiplied more slowly, and produced lower yields of amoebae than the monobacterial strain.

Amoebae multiplied more rapidly and produced higher yields in Trypticase–liver broth than in Trypticase–Panmede.

The effect of certain variations in the basic Trypticase–Panmede medium was investigated. Serum stimulated the growth of the axenic strain in Trypticase–Panmede, so that although the initial multiplication rate was not increased, the maximum yields of amoebae were increased to levels that varied according to the concentration of the serum.

The multiplication of the axenic amoebae was depressed by procedures which probably aerated the medium.

I thank Dr L. S. Diamond for axenic strain NIH:200 of E. histolytica, and Professor E. Meerovitch for axenic strain PZ of E. invadens. I am much indebted to Dr P. Whittlestone, of the Department of Animal Pathology, Cambridge, who examined cultures of strain N for the presence of mycoplasmata. The work was carried out while the author was a member of the scientific staff, Medical Research Council.