The clamp sclerites of Pricea multae and other higher monogeneans was fuchsin-positive in Mallory's and Masson's triple stain, and the staining was not affected by detanning agents, suggesting some form of stabilization in the protein. The sclerites were positive in Millon's, Morner's and Xanthoproteic tests for aromatic amino acids, but negative in tests for sulphydryl and disulphide groups. Quinone, phenol and phenol oxidase were absent. They stained with basic dyes such as toluidine blue and methylene blue in the pH range of 3·5–9·5, and also exhibited bluish fluorescence in u.v. light which was not affected by lipid solvents, indicating the presence of dityrosine and recalling the protein present in the ligament cuticle of insects. These features indicate that the clampprotein is stabilized by the formation of dityrosine. It is suggested that this protein may be responsible for the biological properties of the clamp sclerites. This mode of stabilization by tyrosyl residues of the protein, resulting in the formation of dityrosine, is the first record of its kind to be reported in platyhelminths.

Two ascaridoid nematodes occurring in rodents in South-East Asia, namely Porrocaecum ratti and Toxocara mackerrasae, were compared; the former was redescribed. These and other ascaridoid species occurring in rodents were classified and it was suggested that relative to the other mammalian orders, the rodents are well endowed with ascaridoids. There is, as yet, insufficient evidence for conjecture as to whether species occurring in rodents represent primitive forms from which the species occurring in predatory animals may have been evolved through host—succession—extension, or whether they have been secondarily derived through loss of a predatory definitive host through host—succession—reduction.

The behaviour of Eimeria acervulina in relation to macrophage activity in chickens was investigated by in vitro and in vivo techniques, with special consideration of the excystation of sporozoites and the fate of intact oocysts and sporocysts inoculated parenterally. In vitro: macrophages obtained from peritoneal washings phagocytosed mechanically released sporocysts or previously excysted sporozoites after 30 minutes incubation. In vivo: phagocytic activity of macrophages against intact oocysts and sporocysts in diffusion chambers implanted subcutaneously and intraperitoneally was observed as early as 4 h after implantation. Changes in the oocyst wall (corrugation, thinning, indentation and increased. fragility) as well as activation and excystation of sporozoites in situ was observed 24 h after implantation. Interaction in vivo between the invasive sporozoite and the phagocytic cell was recorded. Disintegration of the parasite was noticed 72 h after implantation.

798 cattle from the Ikoma area, Musoma district, were examined for evidence of trypanosomiasis and the predominant trypanosome species involved.

From the results, the extent of cattle trypanosomiasis in Ikoma and the predominance of congolense-type infections as compared with vivax-type infections was established.

The need to use more than one method in the diagnosis of animal trypanosomiasis is emphasized from the results presented in Table 3.

The direct relationship between the poor health of the cattle and T. congolense infections demonstrates the economic importance of this trypanosome species as compared with T. vivax. This relationship also supports results of earlier work showing that in East Africa congolense-type infections produce more serious clinical trypanosomiasis in cattle than do vivax-type infections. This is important when drawing up a treatment programme.

Sheep in which abomasal fundic pouches had been made were infected with Ostertagia circumcincta (150000 larvae in one sheep, 100000 in three sheep). Subsequently studies were made on pouch secretion, food intake, plasma pepsinogens and abomasal pouch secretory responses when the sheep first ate. A functional abomasal lesion was apparent within 4 days of infection judged by the changes in plasma pepsinogen levels and the sodium concentrations of abomasal contents. Whereas the secretory activity of the abomasal fundic pouches (never exposed to parasites) was maintained or increased, the pH and sodium concentration of contents taken from the infected part of the abomasum were indicative of either a failure to secrete or of a permeability reabsorptive lesion. Ultrastructural studies demonstrated that parietal cells of the pouches had the appearance of cells subjected to strong secretory stimuli, but those of infected abomasa were similar to cells of gastric mucosa subjected to agents suppressing secretion. Factors which might operate, on the one hand, to stimulate secretion from separated fundic abomasal pouches, and on the other to inhibit or modify the secretory activity of the fundic mucosa of the infected abomasa, are discussed.

The embryonic epithelium in Hymenolepis diminuta appears in the early preoncosphere stage. Inside the embryo there is a binucleate cell connected by a cytoplasmic strand with an epithelial layer spreading over the embryonic surface. After the embryo has become covered by tine epithelium the latter delammates into three layers. A basal layer resting on the basal lamina accumulates dense bodies. These bodies are spheroid and membrane-bound in the early embryo. In the late preoncosphere stage rodlike bodies remain in the basal epithelial layer. The basal membrane forms long invaginations into the basal layer. The intermediate epithelial layer is rich in polysomes and it is postulated that secretes extracellular material which cements the intermediate and peripheral layers and the ‘oncospheral membrane’. The continuity in embryonic, larval and adult cestode epithelium is discussed.

Hepatojarakus bandicoti sp.nov. has been described from Bandicota bengalensis (type host), Millardia meltada, Tatera indica and Mus musculus bactrianus. The genus Hepatojarakus Yeh, 1955, has been retained in the family Trichostrongylidae Leiper, 1912. This is the second record of Hepatojarakus and the first from India.

The series of egg envelopes around the acanthor in the mature egg of the palaeacanthocephalan, Polymorphus minutus, has been investigated with light and electron microscopy. An attempt has been made to characterize the macromolecules from which the envelopes are constructed using histochemistry, an analysis of stabilizing bond types and comparisons of envelope fine structure with that of other structural protein systems. The outermost envelope (I) of the mature Polymorphus egg is a fertilization membrane. It is produced by membrane-bounded inclusions in the cytoplasm of the unfertilized oocyte which discharge their contents into the extracellular space around the egg. Envelope II is composed largely of keratin, and its subzones consist of different packing arrangements of 8 nm diameter electron-lucid filaments in an electron-dense matrix. The electron microscopical appearances which this filamentous keratin can present due to section orientation artefacts are discussed. The innermost envelope (III) is 20–30 nm thick and highly corrugated. The spaces between envelopes I and II and between envelope III and the inner surface of envelope II contain material with a granular or fibrous ultrastructure. These spaces show histochemical evidence for the presence of acid mucopolysaccharides.

In a survey of animal trypanosomiasis in Musoma District, carried out in October and November 1970, 6344 G. swynnertoni were collected from six different localities of the Ikoma-Serengeti area and 623 G. pallidipes from Ikoma. These were dissected and examined for trypanosome infections. The mean infection rates of vivax-type in G. swynnertoni and G. pallidipes were 12.6% and 7.5%, respectively. The congolense group infection rates were 2.0% in G. swynnertoni and 1.8% in G. pallidipes. No salivary gland infection was encountered. The incidence of vivax- and congolense-type infections in general increased with age of both the tsetse species, suggesting that the latter can become infected with these trypanosome types at all ages. The infection rate among female tsetse was higher than among males in the six wing-fray categories. This was due to the slower rate of fraying of the wings with age of the former, so that at each wing-fray category the females were generally older than the males. Vivax-type greatly exceeded congolense-type infection rate in both G. swynnertoni and G. pallidipes. It is suggested that this probably reflects the known greater infectivity of the former group of trypanosomes to Glossina. It is concluded that in Ikoma, where game functions as the reservoir of animal trypanosomiasis and where infected tsetse are abundant, the domestic animals are exposed to a continuous trypanosome challenge.

The immune reaction of larvae of D. algonquin against P. bochei was characterized either by the melanization and encapsulation of the parasites or by the production of melanized particles. In successful host reactions the eggs of the parasite were killed before they were completely melanized and encapsulated by haemocytes. When host larvae were transferred during the early stages of infection to a diet that contained phenylthiourea (PTU), the incidence of melanization and encapsulation of the parasites was significantly reduced. However, if the hosts were transferred to the diet just before the eggs of the parasite were normally melanized, PTU had virtually no inhibitory effect, and the immune reaction rate remained very high. These results suggest that the biochemical reactions associated with melanization constitute an important part of the immune reaction of D. algonquin. The data provide additional evidence to support the idea advanced by other workers that the phenoloxidase system plays an important role in insect immunity against some internal metazoan parasites. It is suggested that, during infection, the phenoloxidase system of the haemocytes is activated by hormonal imbalance.

Experiments to study the effect of extrinsic factors on the copulation of normal adult Nippostrongylus brasiliensis are described. Worms copulated when in contact with the rat small intestine, whether it was ligatured, maintained inside or outside the peritoneal cavity, slit open or its lumen obstructed, provided that the blood supply remained intact and the temperature was within a few degrees of normal. Copulation did not occur in the colon, pleural cavity, peritoneal cavity, pregnant or non-pregnant uterus of the live rat or under a variety of in vitro conditions. These results indicate the importance of extrinsic factors for successful copulation since all the worms used in the experiments were intrinsically ready for immediate copulation in their normal environment. Worms observed during in vitro experiments were more vigorous and erratic in their movements than worms in their normal environment. The possible significance of this observation is discussed both in the context of in vitro reproduction experiments and in vitro experiments to study the physiology and biochemistry of the worm.

Trypanosomes were isolated before and after the formation of infected detectable antibody from various brain sites and the blood of Microtus montanus. All isolates were serotyped by the agglutination reaction, and the isolates obtained prior to antibody formation were serologically identical to the original inoculum. Later isolates obtained from separate sites of an infected animal were serologically different from the original inoculum and also from each other. It was therefore concluded that in a single chronically infected animal there are numerous different antigenic populations of trypanosomes each occupying separate brain sites. A hypothesis to account for this antigenic diversity is given.

Lipid levels of infective larvae of Ancylostoma tubaeforme are reduced and their behavioural activity declines with age. We have measured behavioural activity using the percentage active, rate of activity, and the percentage of larvae able to penetrate a membrane. Neostigmine bromide, a cholinergic drug, increased larval activity in all tests. Larvae, stored at 4 and 10 °C and in hypertonic saline, were inactive but consumed lipid. When returned to isotonic saline at 26 °C, these larvae were no more active than those at 26 °C throughout. We found no evidence that such inactive larvae had entered a state of quiescence. All our results, and those of other workers, have been used to emphasize that larval ageing is related directly to decreased metabolic rates, and not primarily to lipid levels.

The free pool amino acids of Taenia crassiceps metacestodes (advanced larvae) were analyzed quantitatively. In addition, the uptake of L-glutamic acid, L-proline, L-phenylalanine, L-lysine, and L-methionine was studied. Proline and glutamic acid absorption followed straight-line kinetics with respect to substrate concentration, and were not inhibited by their own molecular species. Lysine, phenylalanine and methionine were found to enter larvae by a combination of diffusion and mediated processes. Lysine absorption was inhibited only by lysine, arginine and ornithine. Phenylalanine and methionine uptake was not inhibited by lysine or arginine, but was inhibited by several other amino acids. The data suggested the presence of a basic amino acid transport locus and two distinct transport loci for methionine absorption. In addition, both immature and advanced larvae were found to be impermeable to [14C]inulin (M.W. ca. 5000). These results are discussed and compared with the results of earlier investigations of protein and amino acid absorption by T. crassiceps larvae.

Fourth-stage larvae of Toxocara canis were introduced directly into the intestine of previously immunized puppies after laparotomy. They developed normally to the adult stage. In general 46–60% of the introduced larvae completed their development. By contrast the second-stage larvae introduced into similarly immunized puppies did not develop any further. No fourth-stage larvae or adult stages were noted in the nonimmunized controls. The post-immunization sera of puppies formed precipitates at the oral orifices of the second-stage but not of the fourth-stage larvae and antibody response was detected following infection with large doses of infective ova but not small doses of infective ova or fourth-stage larvae.

The phenomenon of self-cure, as it occurred under field conditions in East Africa, was studied in Merino sheep infected with Haemonchus contortus. The onset of self-cure, as judged by a dramatic fall in faecal egg counts, was found to be simultaneous in sheep grazing on infected pasture and in sheep grazing on parasite-free pasture. Furthermore the results of autopsies carried out before and after self-cure showed that a marked and equal loss of adult worm burdens had also occurred. These results indicate that self-cure of H. contortus infections under natural conditions occurs in the absence of reinfection and is apparently non-immunological in origin. Since the phenomenon was always associated with a period of significant rainfall, it is suggested that new growth of pasture may be a significant aetiological factor.

The encapsulation of Trichinella spiralis larvae in host striated muscle was studied.

Capsule formation starts at 13 days post-infection. Between days 20–50 p.i. the largest increase in capsule formation was observed. The capsule is exclusively, or almost exclusively, formed from and by the infected muscle fibre, as might be concluded from the presence of the sarcolemmal basal lamina surrounding the capsule substance during the initial stages of capsule formation. A collagen nature of the capsule cannot be excluded.

Cysticercoids of three species of Tatria have been recovered from the haemocoele of two species of damsel-fly nymphs from a lake in Mid-Wales. This is the first record of Tatria in Britain. The cysticercoids are enclosed each in a transparent capsule of host origin permanently attached to the midgut of the host. The cysticercoids of the three species are indistinguishable superficially. Specific diagnosis depending on the armature of the scolex. Tatria octacantha sp.nov. differs from the other eight species by the presence of eight apical rostellar hooks and 48 small spines on the rostellar surface. One mature adult was found in a little grebe Podiceps ruficollis ruficollis (Pallas) from the same lake and is described briefly. The cysticercoids are described in general terms and the scolex of T. octacantha in detail including the mode of operation of the rostellum and the ultrastructure of the surface layers. A layer of fibres occurs below the superficial longitudinal muscles of the rostellum providing additional support for this mobile organ. A revised key to the nine species of Tatria is included.

The structure and development of the spermatozoon of Dipetalonema viteae has been studied by means of electron microscopy. Spermatogonia are developed from a syncytium in the terminal region of the reproductive tract. The syncytium grows along the length of the testis as an anucleate rachis, carrying with it the developing germ cells. The gametes become detached from the rachis when they have become secondary spermatocytes. The chromosomes which appear in the primary spermatocytes at the onset of meiosis persist throughout all subsequent stages of development. The nucleus is not reconstructed. Cytophores are produced by the spermatids at the end of the second meiotic division. The spermatid is an elongated cell, but the mature spermatozoon, within the male tract, is amoeboid. There are only minor differences between the sperm found in the male and female tracts. The male gametes contain complex membraneous organelles which are developed from the Golgi bodies and endoplasmic reticulum of the primary spermatocytes. These organelles are suggested to have similar origins and functions to the acrosome of the typical mammalian spermatozoon.

A strain of E. tenella which had been passaged serially in 42 batches of chick embryos appeared to have lost its ability to produce the characteristically large second-generation schizonts in both the embryonic chorioallantois and in the chicken caeca. Numerous small schizonts (10–16 µm in diameter), which contained 8–30 small merozoites, replaced the large second-generation schizonts characteristic of this species. The small schizonts were numerous 3–5 days after inoculation and were restricted to epithelial cells of the embryo allantois when sporozoites were inoculated via the allantoic cavity. These schizonts also occurred in epithelial cells of the caeca of chickens given oocysts via the crop. Cell reactions in the chicken caeca in response to infection were minimal. Numerous minute lesions were present in the chorioallantois 4–6 days after inoculation; these were associated with the small schizonts and later with gamonts and oocysts. The strain reproduced well in the embryo but failed to induce gross pathogenic effects and no mortality resulted from the infection.

Only two passages of this strain in chickens were needed to restore a high degree of pathogenicity. This change was accompanied by the reappearance of the characteristically large second-generation schizonts in the tunica propria of the caecal wall.