1. 24: rats were infected with 5,000 N. brasiliensis larvae and were examined hourly from 12 to 24 hours after infection for larvae in the blood and the lymph nodes.

2. Larvae were found in small numbers in the blood and the lymph nodes; the maximum number of positive blood samples occurring sooner after infection than the maximum number of positive lymph nodes.

3. These results were discussed particularly in relation to the timing of the skin to lung migration, and it was concluded that the larvae of N. brasiliensis migrate mainly in the blood but also in the lymph.

1. The morphology of the infective larvae of Cardiofilaria nilesi and Pelecitus sp. in Mansonia crassipes is described in some detail, and sex differences have been noted in them.

2. Infective larvae of C. nilesi can be distinguished from those of Wuchereria bancrofti by the form of the caudal papillae.

3. A brief description is given of four unidentified larvae from other wild-caught mosquitoes in Ceylon.

As a result of their feeding habits, birds of 36 or more families have proved to be susceptible to a large number of dicrocoeliine trematodes living principally in the bile ducts and gall-bladder of their hosts (Faust, 1966). As more species of avian hosts are examined and their liver flukes studied, additional species are described and previously recognized species are reported from new hosts and new geographical areas (Lumsden and Zischke, 1963).

In 1958, Yamaguti differentiated Dicrocoeliinae Looss, 1899 into 8 tribes, one of which he named Lutztrematini, having as cardinal characters an acetabulum much larger than oral sucker and testes tandem or diagonal; single genus Lutztrema Travassos, 1941 and L. obliquum (Travassos, 1917) as type species. The avian dicrocoeliine species described in this communication has important morphological characters agreeing with the Lutztrematini and others lacking agreement. In consequence, it has seemed necessary to create a new genus, Paralutztrema, related to, but generically separate from Lutztrema.

The paper discusses the occurrence of nematodes of the genus Rhabditis in man and reports the finding of specimens of what appears to be Rhabditis (Rhabditella) axei in the urine of an African female in Rhodesia. A discussion is included on the possible method of infection.

Two experiments were undertaken to assess the role of the mouse in the life-cycle of Aelurostrongyhis abslrusus. In the first, 18 mice were fed first stage larvae and killed one month later. At post-mortem and histopathological examinations larvae were not demonstrated and attempts to extract larvae from a proportion of the mice were also negative. In the second experiment, 24 mice were fed heavy doses of first stage larvae. Subsequent examinations failed to reveal the presence of larvae and post-mortem and histopathological examinations performed on two cats, each of which had been fed with six of the mice, failed to reveal the presence of lungworms. It is concluded that mice do not act as intermediate host for Aelurostrongyhis abstrusus.

After five to six weeks, and for a varying period thereafter, cats infested with Aelurostrongylus abstrusus evacuate first stage larvae in their faeces. Hobmaier and Hobmaier (1935), Blaisdell (1952) and MacKerras (1957) collected larvae for eight weeks, two years and seven months, respectively, after patency. Cameron (1927) found that larvae, extracted from faeces, lived for 11 days but were killed by freezing. Since the fate of such larvae is of importance with regard to the incidence of lungworm disease in the cat and because of the divergence of opinion concerning the viability of first stage larvae, it was considered necessary to establish the life-span of such larvae under various controlled conditions.

It has been suggested (Hammond, 1967) that Acanthocephalus ranae absorbs a large proportion of its nutrients through the surface of the trunk, while lipids may be excreted through the surface of the proboscis. The performance of these functions by the proboscis and trunk may well be affected by the mode of attachment of the parasite, and by its behaviour within the host.

The working of the proboscis apparatus of Acanthocephalus ranae has been described (Hammond, 1966a), but its operation in attaching parasite to host has been outlined only briefly (Hammond, 1965).

1. Two new species (Postharmostomum ntowi and Eptsthmium ghanense) and one previously described species (Episthmium africanum) of digenetic trematodes are recorded from the domestic fowl in Ghana.

2. A key has been provided for identification of all the species of Postharmostomum occurring in chickens.

3. Episthmium africanum is recorded for the first time from the domestic fowl.

During the last two decades a number of species have been described in the already large genus Oxyspirura Drasche in Stossich, 1897. Twenty four new species have been described from India alone ; 2 by Singh (1948), 9 by Ali (1960), 4 by Rasheed (1960), 8 by Sultana (1964) and one by Siddiqi and M. S. Jairajpuri (1964). Recently, Oliveira Rodrigues (1962, '63) added 5 species from Brazil and Barus (1963, '65) 2 species, one from U.S.S.R. and the other from Czechoslovakia.

A survey of avian nematodes of Uttar Pradesh in India and Shagunu, Northern Nigeria yielded a number of worms from the orbital cavities of different birds. They represent 14 unidentified species of Oxyspirura and are here described as new.

All measurements are in millimetres unless otherwise stated.

1. The filarial worm Brugia patei was brought to London from East Africa in the larval stage developing in Mansonia mosquitoes. Subsequent transmission to domestic cats was possible in London through a laboratory colony of Mansonia uniformis and the worm was very infective to this species of mosquito. The worm was much less infective to Aedes togoi and Anopheles gambiae.

2. Subsequent passage of the worm through Aedes togoi has increased its infectivity to this species of mosquito. The infection rate has risen from 43·6% in females of A. togoi fed on the cat original- ly infected by larvae from Mansonia mosquitoes, to 59·2% in females fed on a cat containing the first generation of worms to pass through A. togoi, to 79·1% in females fed on cats containing the second generation of worms to pass through A. togoi, to 86·7% in females fed on cats containing the third generation of worms to pass through A. togoi, to 89·8% in females fed on cats containing the fourth generation of worms to pass through A. togoi.

3. The distributions of infective stage larvae in female mosquitoes were negative binomial distributions. These were related to the distributions of microfilarial intake immediately after infection which were also negative binomial. From one generation of worms passed through the new mosquito host to the next the mean and the k value of the negative binomial of the infective stage larvae approached the same parameters for the distribution of microfilarial intake. By the fourth generation of worms passed through A. togoi the distributions of microfilarial intake and infective stage larvae developing in A. togoi were similar, suggesting close adaptation to the new mosquito host. A similar relation between these distributions was found originally in Mansonia. There were however considerable differences in these distributions between the two species of mosquito.

4. The experiment extended over a period of 6 years. The change in infectivity did not appear to be related to the microfilarial density, age of infection, or sex, in the mammalian host. Neither could it be related to the genetics of susceptibility in the mosquito, nor to mosquito culture techniques, nor to mosquito mortality.

5. It is concluded that the observed change in infectivity is best explained by a change in adaptation of the worm to the new intermediate host by selection within the mosquito of those microfilariae adapted to it. No major change in infectivity to the original intermediate host, Mansonia, was found during the experiment.

6. These findings are examined with reference to changes in adaptation to mosquito hosts in the history of Bancroftian filariasis.

Investigations of acquired immunity to Fasciola hepatica in calves, sheep and rabbits are described. With injections of extracts of imma- ture parasites retarded growth of the challenge infection was observed between the 6th and 7th week. Following a previous experience of a natural infection or viable fluke implants, retardation and reduced take of the challenge infection were observed. Considerable individual variation was present and the level of significance between treatment and control groups was low.

1. Ten species of Capillaria are recorded from eight species of British birds. C. blomei from the pheasant and partridge and C. exilis from the rook are new host records.

2. The identity of C. reseda and the systematics of C. blotnei, C. bursata and C. caudinflata are discussed in the light of observations made upon material in the collection.