Ultra-thin sections and electron microscopy have been used in a study of the empty membranes which occur in the fatbody cells of the larva of T. paludosa infected with the Tipula Iridescent Virus (TIV).

It has been observed that these empty membranes are most numerous in the early stages of infection. Later an apparent ‘primary body’, which may be threadlike in its initial stages, develops in the centre of the membrane. This primary body seems to increase in size until the membrane is filled, and the various steps in this process can easily be seen.

It is suggested that the formation of the empty membranes and the apparent gradual development of their contents are the means by which the virus multiplies.

The remarkable resemblance between the empty virus membranes and the endoplasmic reticulum is pointed out.

1. Blood-stream forms of Trypanosoma brucei ‘O’ strain from infected rats were separated from the blood by differential centrifugation. After washing, the trypanosomes were suspended in modified Ringer-phosphate solution with 0·2m glucose, and normal or immune rabbit serum was added. The oxygen uptake of such trypanosome suspensions was measured at 37° C. for 2 hr. with differential manometers using microflasks of 5 ml. capacity.

2. Immune sera that affected the motility of the trypanosomes also caused a decrease in oxygen uptake.

3. Some trypanosomes appeared to be unaffected by the less active concentrations of immune sera, while other trypanosomes in the same suspension were clumped together or lysed.

4. The most active serum inhibited oxygen uptake less at the highest concentration tested (1/4·5) than at lower concentrations (1/9 and 1/20).

5. This technique was less sensitive than Soltys's method (1957) for demonstrating neutralizing antibodies in the same sera.

1. Two Pseudophyllidea, Bothriocephalus scorpii (Müller) and Clestobothrium crassiceps (Rud.), have been obtained from Scophthalmus maximus (L.) and Merluccius merluccius (L.) respectively, from fishing grounds to the west of the British Isles.

2. The musculature of the scolex in both has been compared relative to the form and mode of function of that organ. All the major groups of muscles are present in both, but their arrangement is modified in C. crassiceps, due to the presence of hemispherical bothria, instead of open grooves, and a sphincter muscle around the bothrial opening.

3. The mode of attachment is discussed briefly in C. crassiceps, and in more detail in B. scorpii, where the structure of the scolex was found to be admirably suited to the form of the host's mucosa. The effect on the mucosa is slight, due to the absence of very powerful muscles and of other specialized adhesive structures.

4. The nervous system of the scolex in both species has been compared, and a fundamental similarity has been found. Modifications in C. crassiceps are associated with shortening of the scolex and the difference in form of the bothria.

5. The excretory system shows the same correlation with the form of the scolex.

The proportion of young honeybees which became infested with Acarapis woodi Rennie rose with an increased degree of infestation of the older bees and increased temperatures. But the most important influence controlling infestation seems to be the frequency with which young and old bees come into contact; this is probably determined by the foraging activity of the bees and the ratio of young bees to old bees; the percentage of infested bees in colonies diminished rapidly during nectar-flows and rose in periods of little nectar-flow.

The mortality of infested bees was only slightly greater than that of non-infested bees and became evident only after the bees had been in prolonged unfavourable circumstances. There were no obvious signs of disease in heavily infested colonies in summer. Colonies with more than about 30 or 40 % of infested bees seemed more likely to die in winter than non-infested colonies, but few colonies became so heavily infested even after a very poor season.