Two new species are described from New Guinea pythons, i.e. Ophidascaris niuginiensis and O. papuanus. The former was from Chondropython viridis and Liasis albertisi, the latter from L. amethistinus. Development of O. niuginiensis in mice involved a primary stage in the liver, a secondary stage in the mesenteric blood vessels and a tertiary stage in the skin, where growth occurred to a length of 50 mm or more. Initial growth, up to 10 mm, of O. papuanus occurred in the liver and body cavity of mice; a secondary growth phase occurred in the body cavity of the python host.

The growth of the three free-living stages of N. dubius was measured in terms of dry and fresh weight. Changes in body water content during moulting were demonstrated by variations in dry weight when expressed as a percentage of fresh weight. The respiration rate of the larvae increased until they became infective, after which time it decreased until five days later no oxygen consumption could be recorded. The inability of all larval stages to withstand anaerobic conditions indicated that their metabolism was essentially aerobic. The relationship between body size and metabolic rate was established for each stage and its significance in relation to the life-cycle discussed.

The biology of the life-cycle of Trichuris suis of the pig is described and discussed together with aspects of the hosi-parasite relationship. Development of the infective L. 1 larval stage within the egg was shown to be influenced by temperature. Following ingestion of infective ova by the pig, all subsequent larval development to the adult stage occurred in the mucosa of the caecum and colon. Eggs hatched in the distal region of the small intestine and throughout the large intestine. Larvae then penetrated the caecum and colonic mucosa via the crypts of Lieberkühn, where they entered the cells lining the crypts. The ensuing histotrophic phase lasted 13 days, during which time a gradual larval migration occurred from the deeper regions of the lamina propria to areas immediately beneath the surface mucosal epithelium. Luminal development was initially seen on day 16 when the posterior extremities of larvae were protruded into the gut lumen; from day 20 the entire posterior body region was exposed, while only the filamentous anterior region of the parasite remained embedded in the mucosal surface. The prepatent period varied from 41 to 47 days. Four moults were observed during development within the host and these occurred on days 10, 16, 20, 32 and 37 (to form the L. 2, L. 3, L. 4 and L. 5 or adult stage respectively). It is suggested that although T. suis may not be an important pathogen in its own right, its activities in the caecal and colonic mucosa may cause sufficient damage to enable secondary pathogenic invaders to become established.

The egg and larval stages of Trichuris suis can be briefly characterized as follows: The egg: barrel shaped, possesses a thick shell consisting of three thick outer layers and an inner thin vitelline membrane, is operculate at each end and is unsegmented and unfertilized when freshly deposited. L. 1 within the egg: presence of an oral spear, a poorly denned oesophagus and an intestinal tract consisting of undifferentiated granulated material. L. 1 within the host: initial differentiation of an oesophagus, cell body, intestine and rectum. L. 2: further differentiation of the body organs and the appearance of the rudiments of the reproductive system. L. 3: initial development of reproductive system and development of a cloaca in the male thus distinguishing the sexes. L. 4: differentiation of reproductive system into vagina, uterus, oviduct and ovary in the female, and testis, vas deferens, ejaculatory duct, spicule and spicular muscle, sheath and tube in the male. L. 5 or adult stage: completed development of the sexual organs including formation of the vulval orifice and eggs in the female and seminal vesicle in the male.

Experiments using chicks of specified strain, age and sex raised under identical conditions on the same diet and infected with known strains of coccidia are described. The relationships between the infection rates and resulting oocyst productions of Eimeria acervulina and E. tenella are presented graphically and are used to demonstrate a crowding effect. Possible contributory factors to the crowding effect and possible reasons for the differences between the E. acervulina oocyst production of unmedicated birds or birds medicated with decoquinate are discussed. It is suggested that standard curves for normal infection rate — reproductive potential relationships under strictly specified conditions may be of value in choosing appropriate infection rates for critical experimental work to assess the effects of anticoccidial compounds on oocyst production.

Alteration of the free amino acid pool of Hymenolepis diminuta was observed following incubation of worms with a single exogenous amino acid in vitro, recovery from which depended upon the initial magnitude of alteration. The free amino acid pool of both rat small intestine and H. diminuta was rendered imbalanced after feeding a single dietary dose of proline. Recovery was more rapid in the host than in the parasite tissues. The quantitative dynamics of amino acid change with time were examined. The effects of amino acid variation upon the uptake and incorporation of lysine-C14 into worm protein were examined in vitro. Four amino acids altered lysine incorporation; aspartate stimulated incorporation while ornithine, arginine and histidine reduced variously the absolute amount of lysine uptake but produced relative stimulation of lysine incorporation. These data indicate that, in the system examined, short term variation of the free amino acid pool is unlikely to affect protein synthesis in H. diminuta. Data were obtained suggesting the possible occurrence of certain amino acid inter conversions in H. diminuta.

Duodenal mucosae of uninfected lambs and lambs inoculated at least 16 days earlier with 85000–140000 Trichostrongylus colubriformis larvae were examined with the scanning electron microscope. Normal duodenum had tall spatulate villi with surface folds upon which goblet cells and a regular pattern of hexagonal enterocytes were seen. Micro villi on normal enterocytes were closely packed and imparted a granular surface texture. In heavily infected areas of gut the villi were atrophic, the mucosa sometimes being composed of irregular masses and ridges, with crypt mouths, often surrounded by collars of cells, opening into the surface. More severely affected mucosae were flat, with protuberant collars of cells surrounding crypt mouths. There were rounded bodies, interpreted as sloughing enterocytes, or inflammatory cells, on the mucosal surface. Apices of enterocytes were domed and microvilli were sparse and irregular. Micro-organisms were numerous on cell surfaces. Nematodes were located in sinuous thin-walled tunnels in the epithelium. The mucosal microtopography is compared with that of coeliac disease of humans, nippostrongylosis in rats and with villus atrophy in pigs.

Semi-defined and defined media for the growth of culture forms of Trypanosoma brucei sspp. have been developed by enrichment of tissue culture medium 199 with additional vitamins, amino acids, salts and other compounds. The semi-defined medium contains an acid hydrolysate of casein: in the empirically devised defined medium the casein requirement has been circumvented by inclusion of additional vitamins and amino acids. Both media are very hypertonic. Control of pH was found to be particularly critical for growth. The optimum temperature for growth in the semidefined medium was between 25°C and 28°C, but cells would undergo one or two division cycles at 37°C.

Daily infection with doses of approximately five oocysts of Eimeria tenella produced an infection with an extended patency which ceased by the time the birds had received about 140 oocysts. Total oocyst production was comparable with that in birds given the same number of oocysts in a single dose, but the immunity to subsequent heavy challenge was significantly greater. Continuous exposure to low-level infections may be more comparable to the field situation and the present results suggest how birds can acquire a strong immunity without showing evidence of clinical disease.

Bucephalus haimeanus is shown to be an estuarine species. The cercaria from Cardium edule is briefly redescribed to include details of the nephridial system. The metacercaria is described for the first time, having been obtained experimentally in Pomatoschistus microps and Pleuronectes platessa. In Pomatoschistus microps it survives at least 10 months, development within this host being completed within 2 months. The main site of infection is the liver. Migration is completed within 1 h and in some instances within 10 min. During this period the metacercaria actively feeds on host tissue, the gut being greatly distended with food on encystment. A hyaline cyst wall is maintained throughout the remaining life of the metacercaria. ‘O’ group plaice are highly susceptible to invasion by B. haimeanus during early summer and 100% infections were recorded in catches from Ynys-las, Dovey Estuary, in June. Experiments showed that only 2% of the metacercariae survived more than two weeks and that ‘l’ group plaice were non-susceptible to infection. Plaice are therefore considered accidental hosts. The metacercaria was linked with the adult stage from Morone labrax on the basis of comparative morphology and the ecology of the hosts, the bass entering the estuarine habitat during the summer months. The adult is considered synonymous with Bucephalus minimus Stossich, 1887.

Samples of approximately five wild rabbits were obtained each week over the 4-year period 1967–70, and their intestines examined for adult tapeworms. Pour species of anoplocephalinae were found, Cittotaenia pectinata, C. denticulata, C. ctenoides and Andrya cuniculi. C. pectinata was found in 29% of the 968 rabbits examined, C. denticulata in 14%, C. ctenoides in 12% and A. cuniculi in 6%. There were 63 double infections, of which 44 involved A. cuniculi, and three triple infections. The most frequent number of worms per infection was one for C. pectinata and A. cuniculi and two for C. denticulata and C. clenoides, although the mean numbers for these species were respectively 7·2, 5·3, 2·7 and 1·8. A. cuniculi, and to a lesser extent C. ctenoides, were very restricted in distribution within the study area, occurring only on the higher, chalk downland (250–550 ft A.S.L.). This finding implies that individual rabbits usually spend their lives within relatively small areas. Considering all the material a seasonal trend in host infection rate was apparent only with C. denticulata, which increased in abundance from July to a peak in September and then declined gradually to a low level, lasting from April to June. Infections, including small specimens of any of the four species, were rare from February to June and it is presumed that infected intermediate hosts were correspondingly rare during this period. Except for C. denticulata, which was found more frequently in male rabbits than females, the sex of the host had no influence on its likelihood of infection. However, except for C. pectinata, the age of the host was important. Thus, C. denticulata and A. cuniculi were significantly more frequent in juveniles than adults whilst the reverse was true for C. ctenoides. Small (‘young’) specimens of C. denticulata and A. cuniculi were more frequent in juvenile than adult rabbits, but the difference was not significant for the other two species. It is concluded that only C. ctenoides survives for more than a year and that this species and C. pectinata are more likely to infect rabbits that are adult than are the other two species.

Prophryxus, a new genus of hemiarthrinid bopyrid from Kenya, is described. The only species, P. globicaudatus, is parasitic upon the shrimp Coralliocaris graminea (Dana). Prophryxus is considered to be most closely related to the genus Hemiarthrus Giard & Bonnier, from which it differs in the morphology of the abdominal appendages. It is most remarkable for the presence of a sucker-like organ on the dorsum of the cephalon, a feature unique in the Bopyridae.

Worms of secondary infections of Raillietina cesticillus established in 10-week-old birds but failed to grow mature strobilae. This was taken as an indication of resistance to the cestode. The resistance was inhibited by the immunosuppressant and anti-inflammatory drug dexamethasone, which prevented the local inflammation around attached scolices characteristic of secondary infections of R. cesticillus. Mast cell hyperactivity and eosinophil infiltration in intestinal tissues and immunofluorescent antibodies in sera of infected birds were also demonstrated. Scolices without strobilae from refractory hosts with both primary and secondary infections regrew their strobilae when transplanted into susceptible hosts.