A description is given of a new species of notodelphyoid copepod which has been designated as Notopterophorus ionthus. It is parasitic or commensal in the branchial cavity of the tunicate Phallusia mamillata Cuvier.

In a former paper (Baylis, 1944) an account was given of some observations on the life-history of Mermis nigrescens, and of its occurrence, naturally and experimentally, in earwigs (Forficula auricularia). As stated in that paper, the material then available did not seem to warrant an attempt to describe the larval development. Further material has now been obtained and studied, and it seems desirable to place on record some of the observations made, although many points still remain obscure.

Infection by a variety of species of intestinal nematode infection gives rise to a wide variation in parasite load within a host population. There has been much investigation into the basis of this variation and is thought to involve several factors. Studies of infections of gut dwelling nematodes in laboratory rodents has clearly demonstrated that this variation may be due to the production of cytokines produced as part of the host immune response to infection. More specifically, activation of distinct T helper cell subsets leads to the generation of effective or ineffective responses resulting in clearance of the parasite load or maintenance of chronic infection. The induction of differential responses remains to be determined but is likely to be influenced at a number of levels including involvement of accessory cells and activation of co-stimulatory molecules on antigen presenting cells. Moreover, it appears that these parasites may actively interfere with the host cytokine response to promote their own survival. This review concentrates on recent findings of cytokine mediated control of intestinal nematodes highlighting a central role for the immune system in regulating both acute and chronic infection by these parasites.

The cercaria of Trichobilharzia ocellata finds and identifies its duck host with a seriesof different behavioural phases. Dispersal and selection of the water surface as microhabitat is achieved by an intermittent swimming behaviour, which is governed by the interplay of passive dropping with forward and backward swimming movements and includes a positive phototactic and a geonegative orientation. Then the cercariae tend to cling to the water surface in an energy-saving resting position. A movement towards the duck feet as the site of entry occurs when shadows evoke forward swimming movements, which are directed away from the source of light, i.e. normally downwards. Forward swimming movements are also stimulated by touch, but only in free-swimming cercariae and not when these are in the resting position. Attachments occur only when a substrate is touched during forward swimming movements. Attachments are stimulated by warm substrates (1 °C temperature difference triggers a nearly maximal response) and by chemical components of duck-foot skin, and the readiness to attach is increased when the forward swimming movement is started by shadow stimuli.

1. Nearly a quarter of a million eggs of Sialis lutaria were collected at Cambridge in 1936. About 0·6 per cent of them were attacked by a parasite.

2. The egg-parasite of Sialis is distinct from Trichogramma evanescens, and is to be called T. semblidis (Aurivillius).

3. The male of Trichogramma semblidis occurs in two forms. Neither consists merely of imperfect or degenerate individuals of the other, for the two forms are equally large and differ constantly and fundamentally in several characters. The species, therefore, exhibits true dimorphism.

4. Rearing experiments involving isolated pure lines show that it is principally the host that determines which form of the parasite shall emerge. Males reared on Sialis are of the apterous form; those reared on three species of Lepidoptera are of the winged form.

5. The dimorphism of T. semblidis is discussed in relation to other examples of dimorphism in the Hymenoptera. It is shown to have several features of special interest.

The object of the present investigation was a more complete description of the structure, and the elucidation of the life cycle, of Cercaria mehrai Faruqui, 1930, which was found to infect about 50% of snails, Indoplanorbis exustus, in the Allahabad district during the months of July to December.

Serum-free media were used to culture Plasmodium falciparum. A commercial preparation, Daigo's GF21 developed as a growth-promoting factor for many kinds of mammalian cells, and consisting of the 55–70% ammonium sulphate fraction of adult bovine serum, insulin, transferrin, ethanolamine and sodium selenite, was found to sustain growth of the parasite when Daigo's T was employed as a basal medium. The optimal Daigo's GF21 concentration for parasite growth was between 5 and 20% (v/v), with the best results at 10%. Differential counts indicated that Daigo's GF21 is essential for schizogony. Established serum-free medium, GIT, consisting of Daigo's T basal medium and Daigo's GF21, yielded good parasite growth without any supplementation. Growth-promoting factor derived from adult bovine serum in Daigo's GF21 was shown to be crucial to parasite growth. The results presented here will not only be of practical value, but will provide important information about the developmental requirements for the parasite.

The problems caused by tick and tick-borne diseases for livestock particularly cattle on the African continent are described and discussed. The control of ticks and tick-borne diseases must receive high priority in Africa with regard to both research and control application because of their widespread distribution in areas of high livestock potential and productivity. The conventional methods of tick and tick-borne disease control are discussed and are found to be inadequate in the conditions prevailing in Africa. Methods of integrated control are suggested and discussed in light of recent development in control methods and those still under development. Any one of these methods may not be adequate to control the problem on its own but when several of the methods are combined an economic and robust integrated control is likely to result. Encouragement is given to attempt this approach in Africa to solve what must be the largest animal health problem of livestock remaining in the world.

A new haemogregarine, Schellackia landauae sp.nov., is described in the Brazilian lizard Polychrus marmoratus (Linn) from Pará State, north Brazil. Sporozoites are found principally in the red blood cells (84%) in the peripheral blood but also occur in lymphocytes and monocytes. Experimental transmission to three uninfected P. marmoratus was achieved after feeding them with laboratory-bred Culex pipiens fatigans which had engorged on an infected lizard 14 days previously. The cycle of development in the small intestine of P. marmoratus takes approximately 30 days: schizogony, gametogony and fertilization of the macrogametocytes is in the epithelial cells of the gut, with zygotes penetrating the lamina propria, where the mature oocysts develop. Living oocysts average 14·3 × 13·3 μm, and are approximately 10·0 μm as seen in histological sections. During the period of intestinal development, the parasite also undergoes asexual multiplication within cells of the spleen and liver by a process which appears to be endodyogeny. The exact time required before the first invasion of the peripheral blood by the sporozoites remains to be ascertained, but is some time within 30–45 days after the lizard ingests the infected mosquitoes. Morphology of the sporozoite in the vertebrate host is variable and depends on the host cell occupied; there may be 1 or 2 refractile bodies. Reduction or fusion of these to a single refractile body in those sporozoites within the gut cells of the infected mosquito suggests that the bodies may represent some form of energy source that is used up during this latent phase in the insect vector. Accumulation of sporozoites takes place in the reticulo-endothelial cells of the viscera, in particular the pigmentladen cells of the liver and lung. Attempts to infect other species of lizards, Tropidurus torquatus (Iguanidae) and Ameiva ameiva (Teiidae) failed.

1. In an alkaline inorganic solution containing borate, no bacterial disintegration of tissues occurs in a week.

2. Survival is prolonged by adding sugars to this solution, but not by the addition of bile salt or peptone. Monosaccharides are more effective than disaccharides, and both may enter the worm through its body wall.

3. The effect of variations in certain physicochemical conditions was studied. Wide ranges of osmotic pressure, of the K/Naratio, and of the Ca/Na ratio, have little effect on the worms. The optimum pH is c. 8.4, and t h e optimum temperature c. 36° C. Approximately anaerobic conditions decrease the survival time.

4. The effect of various bactericides, bacteriostatics and anthelmintics upon the worm were investigated in a preliminary manner. Many bactericides are toxic, certain anthelmintics are not. Survival is prolonged by 1/5000 trypan blue.

5. A satisfactory medium for large-scale ‘culturing’ is: NaCl 150 mM., KC1 10 mM., CaCl2 1 mM., borax 6 mM., glucose 30 mM. (pH 8.6). In this the worms survive for c. 60 hr. at a temperature of 36° C.

The reaction of Balb/c mice to primary and secondary subcutaneous infection with chinoeoccu.s granulosus protoscoleces (PSC) is described. From 3 to 14 days following primary exposure to PSC, draining lymph nodes increase in weight and there is expansion of T and B lymphocyte populations, enhancement of in vitro lymphocyte transformational responses and production of PSC-specific 1gM and IgE antibodies. Despite the persistence of viable PSC in host tissues, lymphocyte responses decline to pre-infection values over the period 3–8 weeks post-infection. Secondary exposure to PSC immediately induces lympho proliferation, enhancement of transformational responses, production of IgE antibody and encapsulation of PSC by inflammatory cells. Although specific antibody levels remain high until at least 8 weeks after challenge infection, lymphocyte activity begins to decline after 4 days and is profoundly suppressed by 10 days. Parasite viability appears to be significantly reduced in secondary, as opposed to primary, infection and is associated with the accumulation of large numbers of eosinophils, mast cells and macrophages in infected tissues.

The cirrus of a monogenean Diplectanum aequans was isolated by treatment with sodium carbonate solution and studied with a scanning electron microscope. The method may be used in studies of the functional morphology and taxonomy of other organisms.

Mating was observed in populations of Gyrodactylus turnbulli from guppies. Copulation took place between older (post-1st birth) flukes and resulted in the insemination of spermatozoa into the seminal receptacle. New-born flukes, and flukes which had only recently given birth for the first time (in which the penis was absent or developing), were never inseminated. Flukes were promiscuous, copulating with several partners in succession. The occurrence of mating was related to the size, age and crowding of the G. turnbulli population, taking place most frequently when the parasites were most densely crowded upon the peduncle of the fish on days 5 and 6 of the infection. Maximum population size was positively correlated with the number of flukes initiating an infection. As a result, mating began earlier, and continued for longer in populations founded by several parasites rather than those begun by single flukes. These observations are discussed with respect to the population biology of G. turnbulli: it is likely that sexual and asexual reproduction alternate, with sex being important only during phases of epidemic population growth. The significance of sex in gyrodactylids is discussed, and the potential importance of continuous sexual reproduction in G. turnbulli infections on cultivated guppies is noted.

For the purpose of present study, Ceylon may be regarded as presenting two definite climatic zones—the hot low plains and the damp cool tea-bearing area of the central provinces, a district lying between the isothermal lines of 70–75° F. (vide map 1); these two zones are probably the main factors in influencing the distribution of malaria in the island.

The Leptomonas described in this paper has been studied principally in the gut contents and faeces of the larva of the fly, Leia sp., and in moisture obtained from the decaying vegetable matter within which the larvae grow and pupate. The incidence of infection of the larvae has been found to be almost 100 %, only one or two very young specimens being found unparasitized among the hundreds studied.