1. Observations were made on the development and hatching of eggs of Aspiculuris tetraptera in different media, preparatory to experiments investigating the possible occurrence of retrofection in this Oxyurid. Eggs of Enterobius vermicularis were studied under similar conditions.

2. Infective eggs of A. tetraptera were applied to the anal opening of clean mice which were immobilized in cages specially designed to prevent the possibility of oral infection. Of 12 mice treated thus evidence was obtained from 6, by the finding of immature or adult worms in the intestine, that retrofection had taken place. This constitutes the first experimental proof of the occurrence of retrofection in a non-human Oxyurid.

Tests were conducted using a capillary microbalance to estimate the errors introduced as a result of weighing out replicate cyst batches in place of counting.

Experiments with differently sized samples showed that the normal relationship between sample size and accuracy applied to such cases, the error for samples of 100 cysts being usually of the order of less than 10%. There is some evidence that the errors in cyst number introduced as a result of weighing is reflected by an increased error in the larval count, although under the conditions of experiment the increase was barely significant. It is suggested that if replication is increased by 50% or 100% then errors due to inequality in cyst numbers are more than counteracted.

Four samples of D-D were tested at six dosage levels for their nematicidal activity against the potato-root eelworm Heterodera rostochiensis; the treatments were carried out on naturally infested soil in 5-in. pots, viability being estimated by hatching in root diffusate. There was no evidence of there being significant differences between the samples at 50–60% kills, but at higher and lower kills they did appear to differ appreciably from one another in nematicidal activity.

The original McMaster slide (Gordon and Whitlock, 1939) has been extensively used for investigations involving dilution counts on helminth ova in faeces. In view of the simplicity inherent in its design and use, attempts have been made to utilize it for obtaining estimates of the viable egg contents of cysts of Heierodera rostochiensis, the use of a modified McMaster slide for this purpose being described by Fenwick (1942). Fenwick's slide differed from the original in that the counting area was marked on the floor of the counting chamber instead of its roof; this modification resulted from the use of water as a diluent instead of semi-saturated brine as used in faecal examinations. The capacity of the original McMaster slide (0·15 ml.) was, however, found to be too small to give a reasonably large count from a batch of 100 cysts unless the degree of dilution was so small that efficient agitation before the withdrawal of a sample for counting was difficult.

1. The investigation shows that the spring increase in worm egg output of Scottish hill sheep is correlated with an increase in worm burden.

2. The increase is mainly due to members of the Trichostrongylidae, and of these the stomach worms, Ostertagia spp. and Trichostrongylus axei, are the most important.

8. This increase in the worm burden in the spring is due to larvae picked up at that time, and there was no evidence that any were lying dormant throughout the winter in the mucous membrane of the abomasum and small intestine.

1. An experiment in bush-clearing was carried out at a small endemic focus of onchocerciasis in South Kavirondo district with a view to observing its effect on the adult population of S. neavei.

2. The clearing consisted of the complete removal of undergrowth and partial removal of trees, from the banks of fly-infested portions of two confluent rivers, the Riana and the Yabe.

3. In the first year of the experiment the clearing was carried out on the infested section of the Riana River, after which there was a decrease in the incidence of S. neavei on this section compared with that on the uncleared Yabe River.

4. In the second year a similar clearing was effected on the infested section of the Yabe River, after which the S. neavei incidence on both sections came together again and during the third year showed a steady increase.

An account is given of further observations on the distribution of the beet eelworm (Heterodera schachtii Schm.) in the period 1944–1950. Scattered infections occur in eastern England from South Yorkshire to the Thames and outlying infections suggest that the eelworm may be more generally dispersed. As yet, there are no records of beet eelworm occurring in Scotland. The limitations of the method of field survey are briefly discussed.