1. The free-swimming larvae of Mytilicola intestinalis can develop in theabsence of external food. Approximate figures are given for the duration of the free-living and early parasitic stages.

2. Four of the twenty-one samples of Mytilus edulis collected from various parts of Ireland were infected with Mytilicola intestinalis. All the four mussel beds found to be infected were in the neighbourhood of ports.

3. 72·0% of the Mytilicola which were found inhabited the part of the recurrent intestine which is embedded in the digestive gland.

4. There is a significant correlation between mussel length and number of Mytilicola per mussel.

5. There is a significant decrease in the numbers of Mytilicola per mussel between November to December and May to June. It is almost certain that this represents a real decrease in the copepod population, especially in the mussels larger than 55 mm., due to a death-rate which is sufficient to more than offset the increment due to new infection during November to January. In certain chosen size groups of mussels there is also an apparent decrease as a result of mussel growth in the summer, a time when new infection is very small.

6. In the 50–69 mm. mussel group the number of adult Mytilicola per mussel was lowest in September. The number of immature stages was highest in November and December and lowest from May to August. Egg-bearing copepods were found through out the year. There was an excess of males in the adult population throughout the year.

The writer is very indebted to the various people who assisted in collecting mussel samples especially the Irish Sea Fisheries Association; to Miss M. Davidson, B.A., who made a bacteriological examination of a mussel sample; to Dr J. P. Harding for informing him of the specimens of Mytilicola intestinalis in the British Museum collection; and to Prof. J. Brontë Gatenby and Dr J. D. Smyth of Trinity College, Dublin (where this work was carried out), for their suggestions and advice.

Since 1925, when Leigh-Sharpe described Lernaea elegans, the first Asiatic species from Anguilla japonica, four more species were recorded from China and Japan. The species described in the present paper, while differing from these and other known species, forms the first record of the genus from India. Five parasites attached to three fishes (Osphronemus goramy) and twelve removed from their hosts, together with two fish (Catla catla) infested by about eighteen parasites formed the material examined. Colonies of a vorticellid (Carchesium sp.) were found attached to the external portions of the parasites. In some the stalks of the epizoans were woven through by Algae such as Oscillaria, Lyngbya and Calothrix, enmeshing other algae like Cosmaria, Oedogonium and diatoms, and a matted covering was thus formed round the bodies of the parasites.

1. The nauplius, the metanauplius and the first copepodid larva, of Lernaea chackoensis were reared in vitro and are described.

2. The four copepodid larvae obtained by artificial infection of Barbus stigma and Oryzias rubristigma are described.

3. The young females infesting the adult host fishes are described, noting the changes which take place after the copulation of the female larva.

4. The accelerated development of this tropica form and the need for a temporary host to complete the life cycle are discussed.

1. Mytilicola intestindlis (Steuer) was found in 100% of mussels examined from Blyth, Northumberland. These mussels varied in length between 3·5 and 7·5 cm.

2. The degree of infestation varied from two to fifty-nine parasites per mussel.

3. There was an inverse relationship between the condition of mussels of the size group 5·5–5·9 cm. and both the mean number of parasites per mussel and the mean number of parasites over 1·5 mm. in length per mussel.

4. The mean weight of flesh per mussel in the size group 5·5–5·9 cm. (shell length) was 3·206 g. from Blyth (parasitized) and 5·975 g. from Conway (not parasitized).

5. It is concluded that the presence of Mytilicola is associated with a serious reduction of condition in infested mussels.

Two new monogenetic trematodes of the sub-order Polyopisthocotylea Odhner were obtained from the gills of marine fishes. The characters of the first (Vallisiopsis contorta) agree with those of the subfamily Vallisiinae Price (family Discocotylidae Price) except in the presence of accessory sclerites in the clamp skeleton. As the mere presence of accessory sclerites does not justify the creation of a new subfamily, I refer this species to the subfamily Vallisiinae the diagnosis of which should, however, include the presence of accessory sclerites as an additional character. The second species described belongs to the subfamily Gastrocotylinae Sproston (family Microcotylidae Taschenberg).

Five species of lung nematodes of sheep and goats were found in the Levant countries, namely: Dictyocaulus filaria, Cystocaulus ocreatus, Muellerius capillaris, Protostrongylus rufescens and Neostrongylus linearis. Cystocaulus ocreatus is the commonest, while Neostrongylus linearis is very rare. Descriptions of the morphology of the adults and of all the developmental stages of all these species, except the last, are presented. The presence of a small but well-developed bursa of a protostrongylid type in Muellerius capillaris has been established. The life histories of Cystocaulus ocreatus, Muellerius capillaris and Protostrongylus rufescens have been studied and the susceptibility of various snail hosts has been determined. Experimental infections with larvae of Cystocaulus ocreatus and Muellerius capillaris have been induced in eleven species of terrestrial snails and slugs (belonging to seven genera). Only three of these eleven species proved susceptible to infection with larvae of Protostrongylus rufescens. Experimental infections of definitive hosts with these three species have been obtained. Lowering the temperature retards larval development in the snail. The larval development of P. rufescens is especially retarded and its larvae do not develop at all at temperatures lower than 4–8° C. Natural infection of Helicella barbesiana with the larvae of Cystocaulus ocreatus, Muellerius capillaris and Protostrongylus rufescens has been found in the vicinity of Jerusalem.

Two new species of lung nematodes from Near-East mammals are described: Crenosoma lophocara from Erinaceus roumanicus sacer and Stenuroides herpestis from Herpestes ichneumon, the latter species giving rise to establishment of a new genus of the subfamily Pseudaliinae. This species is the only known example of pseudaliin nematode parasitizing a terrestrial host.

1. Activity in Ixodes ricinus was studied by laying down newly emerged ticks in natural clumps of vegetation from which all hosts (with the possible exception of ‘mice’) were excluded. After a period of quiescence the ticks climbed to the ‘active’ position at the vegetation tips. Activity was assessed either by simple observation (in adults which were marked individually) or by ‘brushing’ the vegetation with the hands (nymphs and larvae). 52 % of the adults and 44 % of the nymphs were recovered.

2. The seasonal activity behaviour was followed in three series of ticks set out during May, July and October 1945. The results were used in interpreting the time relations of seasonal activity in ‘wild’ populations. The timing of the activity cycle appears to be largely determined by the availability of unfed ticks rather than by the prevailing meteorological conditions.

3. The diurnal pattern of behaviour in active ticks was closely examined during a 24 hr. period. Many remained at the tips without moving. The others began or ended a phase of activity by night or by day; but among these, the proportion ending a phase at night was significantly greater. This is the main reason for the previously reported diurnal fluctuation of activity in a tick population.

4. Two hundred and seven adult ticks spent, on an average, a total of 9 days at the vegetation tips (individual limits 1 and 54 days). This activity was spread over an ‘active period’ (interval between first and last appearances) averaging 30 days. Very active ticks rarely remained continuously at the tips. The mean number of visits to the tips was 4 (limits 1 and 19), each lasting for an average of 2·5 days. Where long spells of activity alternate with short periods of quiescence, the behaviour is probably regulated by the humidity reaction, the quiescent phase providing an opportunity for restoring the depleted water balance.

5. Newly moulted adult ticks possess reserves of fat adequate for many months of quiescence. During activity these reserves are exhausted in a few weeks or even days. Duration of survival mainly depended on whether the onset of activity was immediate or delayed. Some adults remained quiescent for 1 year before becoming active for the first time.

6. Several types of orientations were observed in the field. In attaining the position at the tips favourable for encountering a host, the gravity response (upward-turning near the tip) is of major importance. The tick avoids wind and direct sunlight by sheltering behind its supporting stem. In sensing the approach of a ‘host’ (the observer's finger) the perception of eddies of warm air is particularly significant. The response (questing, then orientation) is elicited much less readily if the stimulus is applied from the leeward.

Because of its ability to cany diseases, the sheep tick should be classed as one of the most important ectoparasites of British sheep. No reason for the differences between individual susceptibility to infestation has been found.

Commercial arsenical dips are excellent acaricides, but give little protection from reinfestation, and are no better than watery solutions of sodium arsenite at the same concentrations of arsenic. In the work reported, addition of derris to the commercial dip did not improve it.

Coal-tar fractions which were tested were of little value in tick control, and five finely divided inert powders were not acaricidal.

D.D.T. and B.H.C. give promise of being of real value in controlling ticks; since the former is not effective against sheep scab, it is suggested that future research on anti-tick dips be confined to preparations containing B.H.C., the γ content of which is probably about as effective as D.D.T. against ticks when used at a 5 times greater dilution. Two commercial dips containing B.H.C. were found to be of little value.

A method of anti-tick treatment which involves walking sheep through a shallow bath of dip holds great promise.

Treatment of pastures with D.D.T. appeared to have no effect upon the tick population, and neither D.D.T. nor B.H.C. was effective against ticks when administered to sheep per os.

By stocking a pasture with sheep which were dipped sufficiently often to prevent any female tick from engorging, the tick population was almost completely eradicated in one year. Sheep which were born in the pasture in April 1948, and remained there until October 1949, were not dipped during 1949 and, as far as is known, were not at any time infested by ticks. Pastures from which all sheep were excluded gradually lost their tick populations, but a few ticks remained at the end of 3 years. This may be because, in the main enclosure, almost every tick would have an opportunity of attaching on a dipped sheep, and would be killed; in the unstocked enclosures, lack of opportunity to attach on sheep would result in a larger number of ticks infesting wild animals and so a few ticks would be carried over from year to year. This result is unlikely to have any practical application at present, because ridding a small area (e.g. a farm or a valley) of ticks would result in the sheep of that area losing their immunity to tick-borne diseases, and re-introduction of ticks might bring disastrous results. Also, it should be pointed out that work quoted in the text gives the result of an attempt at eradication in one county of Britain. Among other things, the fact that cattle, hare, and deer were absent immediately prohibits application of the results to many other areas of Great Britain. However, it appears that, in the absence of hare and deer, it might be possible to rid an area of ticks by adequate treatment of domestic animals.

It is a pleasure to acknowledge the helpful advice received from Dr H. H. Green of the Veterinary Laboratory at Weybridge, during the course of this work. The work was carried out under the auspices of a coordinating committee of the Agricultural Research Council and is published by permission of that Council, and of the Veterinary Laboratory of the Ministry of Agriculture.

1. Two experiments are described investigating the effects of level of metabolism on (a) resistance to, and (b) recovery from, Notoedric scabies of rats. The progress and severity of the disease was measured by weekly counts of the number of lesions; the metabolic rate in some rats was raised by administration of iodinated casein and in others was depressed by methyl thiouracil.

2. In normal rats, the initial severe phase of the disease was followed by a partial recovery with survival of a smaller population of parasites.

3. This recovery process in established infestations was hastened by elevation and retarded by depression of the metabolic rate.

4. Resistance to the development of severe disease was enhanced by elevation and reduced by depression of the basal metabolic rate.

5. The level of the residual infestation, after the severe phase of the disease had passed, was also affected by the treatment, being decreased by the higher but increased by the lower metabolic rate.

1. Rearing. Larvae of Trombicula autumnalis were fed on young mice (about 8 days old); after 48 hr. at 25° C. they began dropping off fully engorged.

The post-larval stages were reared individually in separate filter-paper cells. At room temperature, 100% R. H., the engorged larvae were actively mobile for about 6–12 days, and for 12–20 days at 30° C., 100% R.H., before entering a quiescent stage (the developing nymphal stage). The nymphs emerged after about 33 days at room temperature, and 25 days at 30° C., from the time the engorged larvae dropped off the host.

Of the nymphs which developed to adults, four fed on a mixture of yeast, molasses, and agar plus chicken faeces; one fed upon the exuded contents of the eggs of Aëdes aegypti; and another fed upon a mixture of all the ingredients mentioned. Young and old nymphs of Trombicula autumnalis appeared to be incapable of feeding upon intact insects' eggs; neither did they show any particular predilection for the exuded contents of insects' eggs offered as a soft mass, and only with some difficulty were they made to introduce this food into the gut. When chicken faeces were offered as food the nymphs did not feed upon it.

A method of ‘forced feeding’ was adopted, that is to say, nymphs were placed upon or guided on to the periphery of the food mass provided. When a nymph moved away it was replaced upon the food, and the process was repeated until the nymph showed signs of introducing the food into the gut. Occasionally a nymph after being placed upon the food remained in situ and fed continuously for about 6–8 hr. until completely engorged.

2. The post-embryonic forms. The features of the stages (the larva nymph and adult), are described with respect to their development and growth.

The transition, or developing stages (the pre-nymph and pre-adult), are closed systems which resemble the pupal stage of a holometabolous insect. The developing mite is enclosed by the cuticular remains of the preceding mobile stage, and a second inner or intermediate cuticle. Large flattened cells of epidermal origin are present, usually lying against the inner surface of the intermediate cuticle. Emergence of the nymph and adult depends upon the combined effects of an active secretion, which causes a disintegration of the intermediate cuticle, and muscular exertion.

3.Dimorphism. Two kinds of dimorphism are shown during the growth of T. autumnalis; sexual dimorphism associated with size, and nymphal dimorphism depending on marked differences in body shape and in the length of the posterior setae.

Both kinds of dimorphism are initiated at the beginning of post-larval life (beginning of nymphal development).

The time which the engorged larva takes to settle is inversely proportional to the size of the post-larval stages; in other words, the amount of activity and accompanying usage of acquired food reserves before the engorged larva settles appear to govern the absolute size of the individual during post-larval life. There is an indication of small forms becoming male and larger ones female.

Two types of nymph (referred to in this paper as α-type and β-type nymphs) were bred from out-wardly identical larvae. The differences in the growth of the body as a whole and the posterior setae, which distinguish the two types of nymph, appear to be of developmental origin.

4. The life cycle in the natural environment. Laboratory findings confirm the view that only one generation is produced each year, but that successive broods are produced throughout the season of incidence.

The disease, Egyptian fever of cattle, has been observed at the Serum Institute, Abbassiah, in Cyrenaican and Cyprus cattle, and less frequently in native Egyptian cattle. The responsible Theileria has been determined as T. annulata (Dzchunkowsky & Luhz, 1904), and both natural and experimental transmission has been demonstrated with Hyalomma excavatum Koch 1844, of Delpy (1949b).

H. excavatum in Egypt is a three-host tick, which hibernates during the winter months in the walls of buildings in the engorged nymphal and fasting adult stages. Transmission has been effected with nymphae and adults, infected in each case by feeding the preceding stage on reacting or recovered cattle. On no occasion has infection been observed to pass through the egg to the larval stage. Infection can also be transmitted by inoculation of the blood of a reacting animal in which schizonts are demonstrable.

Two nematodes, a male and a female, were found in the stomach of a haddock, Gadus aeglefinus Linn.; they were lying close together and protruding from the wall of the stomach into its cavity. They were sent to Mr Stephen Prudhoe of the British Museum (N.H.), who identified them as probably Ascarophis morrhuae van Beneden. The worms were the only two nematodes found in this fish, and on account of their proximity, and the fact that they both belong to the genus Ascarophis, it is assumed that they are a pair. As the male of this species has not apparently been described so far, an account of the single specimen is given below.

In this study Australorbis glabratus from Puerto Rico, the Dominican Republic, Venezuela, Surinam and Brazil, Biomphalaria pfeifferi from Liberia, and B. boissyi from Egypt were exposed to strains of Schistosoma mansoni from Puerto Rico, Venezuela, Surinam and Egypt, and to seven cross-strains of S. mansoni. In many instances, incompatibilities between vectors and parasites of different endemic areas were noted. It is suggested that these incompatibilities might be accounted for in two ways: (1) interspecific and intraspecific differences between vectors in respect to the physiological factors that are responsible for the development of the parasite in the snail, and (2) physiological differences between strains of the parasite. Evidence would seem to show that there are interspecific physiological differences between Australorbis glabratus and Biomphalaria boissyi; and that there are intraspecific differences between Australorbis glabratus from Brazil and A. glabratus from other countries here dealt with. In addition, it would appear that the parasite of Egypt differs physiologically from the parasites of Puerto Rico, Venezuela and Surinam; and that the parasite of Brazil differs physiologically from the parasites of the latter countries.

We wish to express our gratitude to the following persons for their co-operation in collecting and shipping snails for this study: Drs M. Abdel Azim, C. H. Barlow, J. O. Coutinho, A. Gabaldon, the late W. A. Hoffman, G. W. Luttermoser, J. Oliver-Gonzalez, H. A. Poindexter, Bichat de Almeida Rodriques and A. E. Wolff. We are also indebted to the late Dr W. A. Hoffman, Dr M. Mayer and Dr J. Alves Meira for sending us animals infected with Schistosoma mansoni.

The intra-erythrocytic development of a parasite of the frugivorous bat, Roussettus leachi, has been, observed. The name Plasmodium roussetti has been suggested temporarily. The rosettes are typical of the genus Plasmodium. The parasites can be transmitted congenitally and gametocytes have been found in foetal blood.

This work has been made possible by grants from the Fonds National de la Recherche Scientifique and from the Institut pour la Recherche Scientifique en Afrique Centrale.

1. The structure, method of division and cultural requirements of a trichomonad from the gut of Vipera ammodytes L. have been studied; the organism was found, in these respects, to be identical with Trichomonas batrachorum Perty, 1852.

2. Tadpoles of Bufo vulgaris have been infected experimentally with the strain.

3. It is concluded that the trichomonad was a strain of Trichomonas batrachorum established in a reptilian host.

During the collection of helminths from a goat, millet-sized nodules were noticed in the mucous membrane of the abomasum. Examination of these nodules showed that there were no larval nematodes in their substance, but that they contained a large mass of spores. The nodules were identified as cysts belonging to the protozoon parasite, Globidium gilruthi. This parasite has not previously been recorded from the Indo-Pakistan sub-continent. The parasite was for the first time observed by Flesch (1883). Moussu & Marotel (1902) regarded it as a developmental stage of the coccidium, Eimeria faurei. It was studied by Gilruth (1910) and in the same year by Chatton (1910), who named it as Gastrocystis gilruthi.

Schistocephalus solidus is a small avian pseudophyllidean cestode which, on account of its small size and the ease with which its plerocercoid may be cultured to maturity in vitro, has been used within recent years for the study of cestode physiology.

P. malariae was first used for therapy purposes at Horton in 1928.

Between 1928 and 1945, nine strains have been used. Most of these were from Africa, but some were from Holland, Roumania and South America. The strain from Holland was probably not indigenous to that country.

All transmission experiments carried out between 1928 and 1945 were with Anopheles maculipennis var. atroparvus. Nineteen separate batches of mosquitoes were fed on patients in whose blood parasites believed to be gametocytes were seen. In only six of these batches were any of the mosquitoes found to be infected and then with only scanty oocysts; sporozoites were never found. No patients were infected by the bites of any of these mosquitoes.

In 1947 a colony of A. stephensi (type) was established.

From 1948 to 1950, sixty-eight batches of A. stephensi were fed on patients in whose blood Plasmodium malariae parasites were present. Scanty gametocytes were found in some of these patients, and on occasion mosquitoes which fed on them became infected, but in others no infection occurred.

Other batches of mosquitoes did become infected after feeding on patients in whose blood no typical gametocytes were found even after a prolonged search. Out of sixty-eight batches of mosquitoes fed, infection was seen in twelve batches, in varying degree, but never with more than nine oocysts in an individual mosquito. Two consecutive human anopheline passages with laboratory-bred Anopheles mosquitoes (A. stephehsi type) and induced human carriers are reported.

1. A method is described for separating and enumerating the ciliate Protozoa which occur in the large intestine of the horse.

2. The concentration of ciliates varied in the different regions of the large intestine, being low in the caecum and highest in the left dorsal colon.

3. Two distinct populations of ciliates occurred in the large intestine of the horse, one from the caecum to the pelvic flexure and the other from the pelvic flexure to the rectum.