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.

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.

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.

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.

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.

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.

Oogenesis and fertilization in the filarial worm Dipetalonema viteae have been described. The female gametes are developed from a syncytium situated at the posterior tip of the ovary. The syncytium grows along the length of the ovary as an anucleate rachis carrying the germ cells with it. In the germinal region of the ovary the rachis is a central axial structure, but in the growth region it becomes very branched. The female gametes retain their attachment with the rachis until they have become mature primary oocytes; they acquire a surface coat whilst in the growth zone of the ovary. At fertilization the successful spermatozoon produces numerous ribosomes. Residual spermatozoa are apparently destroyed by the oocyte. The fertilized oocyte divides meiotically to yield an ovum and two polar bodies. In species destined to be unsheathed in the blood the surface coat and the original oolemma separate from the surface of the ovum. A new oolemma is produced, presumably under the stimulus of fertilization.

An account is given of the structure and mode of action of the opisthaptor of the monogenean Pseudobenedenia nototheniae Johnston, 1931, from the skin of the fish Notothenia neglecta, caught in December 1969 at a depth of 40 m offSigny Island (60° 43′ S., 45° 36′ W.), South Orkney Islands. The opisthaptor has a roughly hexagonal central loculus surrounded by a septum which is continuous with six radiating septa. It is armed with 14 marginal hooklets and three pairs of sclerites which function as anchors. The opisthaptor obtains adhesion through gripping the host's skin with the muscular rim, and through close contact by the marginal membrane. These form a water-tight seal, the surface area of which is about one-quarter of that of the ventral surface of the opisthaptor. The seal enables the opisthaptor to function as an underwater sucker. Contraction of muscles associated with the opisthaptor, in particular the extrinsic muscles, can generate a pressure difference across the wall of the opisthaptor some 50 times greater than that required to support the weight of the parasite, thus suggesting that reserves are available to resist dislodging forces such as increased water flow. The instability and tendency to slide of the sucker is counteracted by anchorage from the hooklets and sclerites. The structure and mode of action of the opisthaptor of P. nototheniae are discussed in relation to studies made by other authors on similar adhesive organs.

The functional organization of the tail musculature of two species of cercariae has been studied by examination of serial sections in the light and transmission electron microscopes. A three-dimensional reconstruction of the tail has been established. The fine structure of the muscle cells has been investigated and the complexity of organization is related to the requirement for a fast contracting system in the cercarial tail.

Perforated plastic cylinders (hair curlers) were implanted subcutaneously in rabbits for the collection of tissue fluid. Using this technique, a study was made of the chemical constituents of tissue fluid and serum in rabbits infected with Trypanosoma (Trypanozoon) brucei, as compared with uninfected, control animals. Changes were caused by the infection in the concentrations of proteins, electrolytes, urea, creatinine, cholesterol and pyruvate, and in the activities of the enzymes aspartate transaminase, creatine phosphokinase and alkaline phosphatase. Antitrypanosomal antibody, detectable by the indirect fluorescent antibody technique, was shown to penetrate the tissue fluid and to reach a titre of about one-fifth of that in the serum. Renal failure, probably resulting from allergic reactions, was shown to be a contributory cause of death in rabbits infected with T. (T.) brucei.

Mesophryxus, a new genus of phryxid isopod is described. The only species, M. ventralis, is a parasite of Harpiliopsis beaupresi (Audouin) to which it is attached on the ventral aspect of the sixth abdominal segment, behind the fifth pair of pleopods. Mesophryxus is most closely related to the genus Anomophryxus Shiino, from which it differs in the arrangement of appendages on the abdomen.

The kinetics of uracil, thymine, 5-bromouracil, hypoxanthine, guanine and adenine uptake by Hymenolepis diminuta were studied using shortterm (2 min) incubations. The effects of other purines and pyrimidines on the uptake of these compounds was determined. The data suggest that the purine-pyrimidine transport system of H. diminuta contains at least three distinct transport loci and that two of these loci contain multiple substrate binding sites. The three loci are characterized as follows: (1) A thymine-uracil locus which is responsible for the absorption of thymine and uracil via allosteric mechanisms and, therefore, apparently contains two binding sites for these pyrimidines. Adenine and hypoxanthine are non-productively bound to this locus; purine and 6-methyluracil are also bound to this locus, but it is unknown if binding is productive. (2) A locus which transports hypoxanthine (denoted as hypoxanthine locus no. 1), guanine, and adenine. The latter purine is apparently transported by an allosteric mechanism and, therefore, this locus apparently contains two adenine binding sites. Uracil and 5-bromouracil also bind to this locus, however, the nature of binding is uncertain. (3) A second hypoxanthine locus (hypoxanthine locus no. 2) can also be demonstrated which nonproductively binds adenine. Purine is also bound to this locus, but it is unknown if this binding is productive.

Rhipicephalus appendiculatus ticks, infected with Theileria parva, were fed on rabbits and removed at daily intervals for 9 days. Half of the ticks removed were dissected and their salivary glands processed and examined for parasites. The remaining ticks which had been removed were ground up and aliquots of the supernatant fluid thus obtained were injected into East Coast fever susceptible cattle. Cattle injected with supernatant fluids from ticks fed for 4–9 days became infected, and this could be correlated with the histological detection of mature parasites in the corresponding ticks. The most highly infective supernatant fluids were prepared from 5-day-fed ticks. In a second experiment it was shown that female ticks of a variety of weights contained infective particles of T. parva.