An attempt was made to determine if blocking antibody is involved in protecting cysticerci of Taenia taeniaeformis against a host immune response. Immunoflourescence microscopy confirmed that host antibody is present on the parasite surface within the capsule. To test if the larvae can still survive after such a coat of blocking antibody is removed, the larvae were trypsinised and then implanted into recipients. The results indicate that blocking antibody could be involved in the survival of 1 year old established larvae. Untrypsinised larvae were normal 14 days after implantation into control or immunised rats. Trypsinised larvae implanted in control rats were alive but showed on intense cell adherence on their surface. On the other hand, trypsinised larvae implanted into immunised rats were dead and completely encapsulated. However, experiments with 1 month old larvae were inconclusive.

The egg shell of Dipetalonema viteae separated from the oolemma and became highly convoluted at an early stage of development. No second oolemma or trilaminate membrane was seen. Channels containing electron dense material (thought to be nutrient material from the uterine wall) were formed between adjacent embryos. Many developing embryos died.

Microvilli were formed by the uterine wall and developing embryos were closely apposed to these (again presumably to obtain nutrient).

Embryos emerged from the egg in the uterus and were born as unsheathed microfilariae.

The offspring from hybridization experiments between Schistosoma intercalatum, Cameroun (intermediate host Bulinus forskalii) and S. intercalatum, Zaïre (intermediate host B. globosus) was investigated. Reciprocal crosses between the two forms were performed.

F1–and F2– miracidia developed in both parental intermediate hosts. The minimum prepatent period was 24 days at 26°C, an average of the prepatent periods for the two parental strains.

The total cercariae production per 100 exposed snails decreased sharply from 121 000 for the parental strain from Cameroun in B. forskalii to 21 000 and 5000 from the F1–and F2–generations, respectively. The figures for S. intercalatum, Zaïre in B. globosus were 270 000, 134 000 and 3000, respectively. F1–and F2–generations were from the cross between males from Cameroun and females from Zaïre.

The viability of the four cross-breeding experimentas carried out (two with each combinations of the parental strains) were low. It was only possible to obtain F2–cercariae. No miracidia were hatched from eggs produced by the F2–generation.

Diplozoon homoion gracile from the southern barbel (Barbus meridionalis) displays an egg-laying and an egg hatching rhythm, the latter being more clearly defined. Egg laying continues both day and night but significantly more eggs are laid at night. The oncomiracidia hatch at dusk. If parasite eggs are eaten by the host they pass through the gut undamaged and hatch normally.

Allometric growth of body proportions and organs is determined for three species of digenetic trematodes of marine fishes from Belize: Apocreadium mexicanum Manter, 1937 (Apocreadiidae), Pseudocreadium lamelliforme (Linton. 1907) Manter, 1946 (Lepocreadiidae), Paracryptogonimus americanus Manter, 1940 (Cryptogonimidae). These are compared with three other species in which allometric growth has been studied. In all species only the hindbody shows positive growth, whereas the forebody, suckers, and pharynx are consistently negative. The body width, posttesticular body, testes, and ovary are positive in some species and negative in others. In some instances the body proportion or organ is growing at the same rate as the body length.

Viktorocara torea and Sciadiocara tarapunga n. spp. are described from specimens from the gizzards of Haematopus ostralegus finschi and Larus novaehollandiae scopulinus respectively. All hosts were collected in the South Island, New Zealand. V. torea is characterised by the possession of the doubly bifid apices to the long spicule and absence of a subterminal spicular spur; presence of six preanal papillae, the first and second widely spaced: the muscular region of the oesophagus constituting about one quarter of the total length of the oesophagus. S. tarapunga is similar to S. umbellifera, but differs in having the muscular region of the oesophagus shorter than the glandular region, a more slender body in both sexes, much smaller spicules (78–91 μm and 275–359 μm) with the right spicule not more than one-third as long as the left one. The long spicule bears a pair of similar, rounded, laterally placed spatulate apices. It is suggested that Sciadiocara umbellifera of previous authors may encompass more than one species.

The life history of Allocreadium fasciatusi which occurs in the intestine of a freshwater fish Aplocheilus melastigma has been worked out in detail. The snail Amnicola travancorica acts as the first intermediate host. The miracidium hatching out from the eggs attacks the snail and passes through two generations of rediae. Cercariae are of ophthalmoxiphidiocercous type with very long tail and are identical to Cercariae Indicae XLIX Sewell, 1922. The cercariae penetrate and develop into metacercariae in the haemecoel of the copepods Mesocyclops leuckarti, Microcyclops varicans and Marcocyclops distructus. Upon ingestion by the definitive host, the metacercariae excyst and develop into adults. All the stages in the life cycle are described and the life cycle is compared with other allocreadiid life cycles. The original description of A. fasciatusi is revised and Psilostomum chilkai Chatterji, 1956 from Lates calcalifer is synonymized with it.

A study was made on the host-finding capacity of Fasciola hepatica miracidia in relation to time, number of miracidia per snail, and several physico-chemical environmental factors. Specimens of Lymnaea truncatula were exposed to radiolabelled miracidia and the subsequent snail-bound radioactivity was used to measure the host-finding capacity of the larvae.

Maximum snail-bound radioactivity was achieved after 45–60 minutes exposure to miracidia in a volume of 80 ml water. The efficiency of the snail-location was unaltered up to a volume of 4.5 liters. A linear proportionality was demonstrated between the number of miracidia and the amount of radioactivity obtained in exposed snails. After 4 hours exposure snails placed in darkness took up the same amount of radioactivity as snails placed in bright illumination. Additional experiments showed that miracidia preferentially scan the lighted zone of a given environment, but if no snails are available in this zone, snails in shade are also effectively located.

The host-finding capacity was unaltered up to a salinity level of 3.79%. At 4.74% and 5.68% the snail-location proceeded at a slower rate, but the final levels reached after 3 hours were comparable to that obtained at low salinity. The over-all host-finding capacity was reduced at a salinity level of 7.58% and at 9.47% the capacity had ceased. The host-finding capacity was unaltered in the pH range 5.4 to 8.4, but it was reduced at pH 8.9. Further studies showed that the host-finding capacity was clearly inhibited in water with a high turbidity level.

Microfilariae of Onchocerca sweetae are broadly distributed in the superficial layers of the dermis of the water buffalo (Bubalus bubalis). A total of 2855 insects representing 20 species were collected from O. sweetae-infected bait buffaloes. Only one species, Culicoides sp. “M”, ingested microfilariae from buffalo skin. Larval development of O. sweetae was observed in the thorax of this species. A total of 829 insects, representing 7 species and including 749 parous Culicoides spp. were collected from light and Manitoba traps. Developing filarioid larvae were observed only in Culicoides sp. “M”. It is concluded that Culicoides sp. “M” is a natural intermediate host of O. sweetae in the Northern Territory of Australia.

The activity of maltase, saccharase, cellobiase, trehalase and lactase was estimated in the intestinal contents of non-infected pigs and pigs infected with several gastrointestinal nematodes and in the nematodes themselves.

Enzyme activities in the intestinal contents of pigs infected with Hyostrongylus rubidus were similar to those in uninfected control pigs. However the enzyme activity of the contents of the whole intestine was increased in Strongyloides ransomi infections and moderately increased in Ascaris suum infection. In Trichuris and Oesophagostomum infections activity was only increased in the large intestine contents.

Ascaris suum contained high activity of maltase and saccharase in its intestine and lower levels in other organs, while levels were much lower in other pig nematodes. Hyostrongylus rubidus and its third-stage larva did not contain any disaccharidases activity.

The disaccharidases in the pig nematodes, especially in Strongyloides, were more sensitive to high temperatures (70°C) than those in the contents of the pig intestine.

Some disaccharidases were demonstrable in embryonated Ascaris and Trichuris eggs and in third-stage larvae of Strongyloides and Oesophagostomum.

A new species in the genus Goezia is described from aquatic reptiles of the northern shores of Australia, west of Cape York Peninsula. It was collected from Crocodylus porosus, from a file snake (Achrochordus granulatus), and from sea snakes (Lapemis hardwickii, Enhydrina schistosa, Hydrophis elegans, and H. caerulescens). The new species is compared with G. fluviatilis from Australian freshwater fish, with G. minuta from marine fish of the east coast of North America, and with G. spinulosa and G. intermedia from South American freshwater fish. The host-relationships of the genus are discussed.