1. A new genus of trematode (family Allocre-adiidae) from the intestine of freshwater eels is described, and named Stegodexamene anguillae.

2. The genus is related to Aephnidiogenes, Lepidapedon and Neophasis, but differs significantly from each of them.

3. The life cycle followed is from the adult in Anguilla dieffenbachii to the redia in Potamopyrgus antipodum (fresh-water gastropod). The cercaria encysts in the eloetrid fish Gobiomorphus gobioides.

4. Progenetic production of eggs and spermatozoa occurs in the metacercariae.

5. Metacercarial excretory spherules are composed of calcium carbonate.

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.

The material which forms the basis of this paper was obtained from the birds shot at Lashio, Upper Burma, in October 1941. I am greatly indebted to Prof. F. J. Meggitt for his help at Rangoon, in spite of his busy time owing to active field service at that period in Burma, and also for the use of his extensive private library before the general evacuation of 1942.

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.

During investigations of the helminth parasites of the British limpets Patella vulgata, P. intermedia and P. depressa in relation to a possible bearing of parasitism on mortality and sex proportions, three larval trematodes, Cercaria Patellae Lebour, 1911; an unidentified Xiphidiocercaria, Cercaria B; an unidentified Cercaria C; and one larval cestode were found. Of these, C. patellae was the commonest.

Each of the three trematodes occurs independently in the digestive gland, the cestode being encysted on the surface of the visceral mass. The Cercaria C is visible only in smear preparations or sections, but infestations with the other three parasites can usually be seen on removing the limpet's shell. The sporocysts of the Xiphidiocercaria, Cercaria B, are restricted to a limited portion of the digestive gland or, very rarely, of the kidney; the rediae of C. patellae are loosely distributed throughout the visceral mass. No sporocysts of the Cercaria C have been observed.

C. patellae is commonest in Patella depressa, but since in all three species it is more common in populations inhabiting rock pools the apparent preference for P. depressa may be because this species occurs in pools or at low water marks, whereas the other species frequent ‘dry’ habitats.

Most limpets infested with Cercaria Patellae are in the larger size (age) groups. For example, the percentage infestation in Patella depressa at Port St Mary, Isle of Man, is very low in specimens less than 40 mm. in length, increasing to 100% in those of more than 65 mm.

Cercaria Patellae escapes from the limpet by way of the veinlets in the mantle skirt. It is suggested that migration of cercariae within the haemocoele, and subsequent escape from the mantle, may be a common occurrence in other molluscs infested with larval trematodes.

The number of cercariae given off by the limpet in vitro is greatest immediately after immersion in water, the rate of escape then steadily falls and finally ceases after about 30 hr. of immersion. Under natural conditions there is probably a rhythm imposed by tidal fluctuations, the cercariae escaping only when the host is covered by the tide.

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.

In natural grazing grounds, bovines affected with East Coast fever remain ambulatory until a few days or even a few hours before death, and larval and nymphal Rhipicephalus appendwulatus and R. evertsi, which have fed and engorged, will infest the pasture over a wide area. Subsequently, when susceptible cattle graze over this area small numbers of infected instars may attach at intervals and begin to feed. In this experiment an attempt was made to simulate these conditions as closely as possible.

In group A wnere one infected tick was fed on the 1st day, two on the 3rd day, and three on the 21st day, two out of six calves developed an unmistakable East Coast fever infection, with Koch's bodies present in gland smears. In one calf (no. 5724) the reaction was most severe and was undoubtedly due to the three ticks which attached on the 1st and 3rd days, while in another calf (no. 115) the reaction was less severe and was most probably due to the three ticks which attached on the 21st day.

In group B where one infected tick was fed on the 1st day, two on the 5th day, and three on the 21st day; five out of six calves gave a definite unmistakable East Coast fever reaction with Koch's bodies present in gland smears, four of the reactions being undoubtedly due to the three ticks which attached on the 1st and 5th days. There is as yet no reasonable explanation as to why the number of definite reactors should differ so markedly in the two groups.

It is noteworthy that all these reactions were mild and that recovery in each case was uneventful. The only death to occur was control calf no 5729, on which ten infected ticks had fed at one time, but from the results of the other controls it may be assumed that the strain of Theileria parva had by some means become attenuated or that the calves had increased tolerance or resistance.

It is difficult to understand why calf no. 109 failed to react in the first experiment but showed some susceptibility when challenged 96 days later, and why calves nos. 5711, 116, 5642 and 39 gave doubtful reactions. No explanation can be given at this stage, but it raises two practical questions. First, it is difficult to assess the minimum intensity of a reaction which is sufficient to give a durable immunity. The fact that calf no. 114, after what appeared to be a definite T. parva reaction, reacted a second time on exposure to infection 110 days later, proved that the immunity was not prolonged. It is true that the first reaction was only mild, but practically the same remarks could be applied to calves nos. 117 and 5725, yet these calves had not lost their immunity on challenge. Secondly, it is difficult to ensure, by observation of daily temperatures alone, that all calves are really fully susceptible before being used on a critical East Coast fever experiment, for if only a few infected ticks are accidentally introduced into stables or grazing paddocks, it may be assumed that mild subclinical infections will result. These calves may then show varying degrees of resistance to subsequent infections, and results such as those experienced in these experiments would be a normal sequelae.

The intensity of the leucopaenia appeared to bear no relationship to the number of days Koch's bodies were present in gland smears. It was present before the first rise in temperature in all the calves except no. 114, the only calf to show a second reaction on challenge.

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).

This experiment showed that infections of Theileria parva were still viable in nymphae of Rhipicephalus appendictdatus 171 days old, but when nine nymphae were fed on calves at intervals over 22 days the reactions produced were most irregular.

In group A reactions varied from acute fatal type to mild, doubtful or no obvious reaction. None of the four animals which survived was protected from subsequent infection when grazed in a tick-infested paddock (Table 1). The two fatal reactions which developed in this paddock varied in intensity; calf no. 5717 showing a typical acute East Coast fever reaction, but the reaction of calf no. 167 showed several atypical features especially in the sporadic appearance of Koch's bodies.

In group B the reactions were again in marked contrast to those seen in group A, one fatal reaction developed and only mild transient reactions without the production of Koch's bodies were seen in the remaining five calves. These mild reactions, however, appeared to be sufficient to protect against subsequent re-infection in the tick-paddock (Table 4).

It is doubtful if the transient reactions seen in calves nos. 5734 (on the 12th day), 172 and 168 could be diagnosed clinically under field conditions, and further investigations as to the infectivity of these types of reactions are required.

In calves nos. 165 and 167 Koch's bodies were absent from all tissue smears at time of death, and diagnosis of the true cause of death by smears alone would therefore be difficult. Reactions such as those given by calves 133 and 139 cast further doubt on the ability to diagnose East Coast fever by gland-smear technique.

In general, the results of this experiment appear to indicate that if the original reaction is mild a second reaction may develop within a few weeks with or without the production of Koch's bodies. The development of a durable resistance to further attacks may not, therefore, depend on the presence of Koch's bodies in the peripheral glandular tissues in detectable numbers.

My thanks are due to the Director of Veterinary Services, Uganda, for his permission to carry out this work and to publish this paper.

1. The musculature and excretory and nervous systems of Cysticercus taeniae-taeniaeformis are described.

2. The nervous system consists often longitudinal nerve cords in the strobila and of a brain and complicated system of nerves in the scolex. The nervous system of the scolex shows several variations on the earlier description by Bartels (1902).

3. Minor abnormalities have been found in the form of multiplication of the lateral margins and duplication of the ventral excretory vessels.

4. Three specimens showed spiral torsion of the internal organs involving the musculature and excretory and nervous systems of the strobila. The number of turns of the spiral and the positions of the chiasmata are variable. It is suggested that the spiral twisting occurs before growth and strobilation in the neck region has begun, the chiasmata being carried back as new segments are formed.

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.

A linguatulid, very similar to the nymphal ‘Pentastoma gracile’ from crocodiles described by Sambon, was found in faecal material from a European resident in Khartoum. There is no evidence concerning the method of infection.

I am indebted to Dr E. S. Horgan, until recently Director of the Stack Medical Research Laboratories, for his reply to my inquiries concerning linguatulid infections in the Sudan; and to Prof. J. J. C. Butley, of the London School of Hygiene and Tropical Medicine, for his valuable assistance in obtaining relevant literature.

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.

The survival of fasting imagines of Hyalomma savignyi under various conditions of temperature and relative humidity was studied.

Within the range of experimental conditions low temperature and high humidity are shown to be most favourable to the survival of ticks: at 17·5° C. and 80–95% R.H. mean longevity approaches 1 year, and a few individuals were observed to survive for more than 2 years. Longevity shortens as temperature rises and relative humidity decreases. At a temperature of 37° C. (and under various conditions of humidity) average longevity does not exceed 1·5–3·5 months, while under conditions of extreme dryness, viz. 10–20% b.h. (and various temperatures) average longevity ranges from 1·5 to 9 months.

The longevity of fasting imagines is not as much affected by dryness as that of preimaginal stages.

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. The external structure of the capitulum of Ixodes hexagonus is described in detail, and the differences between it and the closely allied I. cookei are noted.

2. The capitulum is divisible into two portions, an extra-basis and basis regions. The former is divided into the hypostomal groove, the labrohypostomal groove and the labro-hypostomal gutter. Internally the basis is divided into dorsal and ventral chambers by the subcheliceral plate. The dorsal chamber houses the chelicerae while the pharynx and the salivary ducts occupy the ventral portion.

3. The so-called ‘stylet-like process’ is the anterior prolongation from the basal lobe of the labrum, and forms the mid-rib of a lamella which divides the hypostome into a dorsal salivary channel and a ventral food conduit.

4. There are rows of teeth on the internal faces of the anterior fifth of the pharynx. Two series of pharyngeal muscles are present: (i) those having a dorsal attachment to the floor of the salivary chamber, and (ii) those having similar attachments to the subcheliceral plates.

5. During feeding the first incision is made by the denticulate apices of the digits and into it the hypostome is then forced. Further cutting by the digits enables the hypostome to penetrate to its base. At the same time the palps splay out. The blood is then drawn up the food conduit by the action of the sucking pharynx. The lower surface of the labrum is produced into a tooth-like projection that fits into a groove of the lower wall of the pharynx. Presumably it functions as a valve to prevent regurgitation of blood. The pharyngeal teeth may function as a supplementary valvular apparatus or else serve for the breakdown of erythrocytes.

6. The tissue reaction of a stoat's skin to penetration by the capitulum of I. hexagonus is described.

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. Ixodes hexagonus is a three-host tick.

2. The length of the pre-oviposition period is fairly constant at 19° C. in a saturated atmosphere, varying between 12 and 14 days.

3. Oviposition takes place as in I. ricinus and, at room temperatures at 18–20° C., R.H. 100%, the number of eggs laid varies from 880 to 1449. Experiments on the effects of different temperatures and humidities on egg-laying are described.

4. Eggs hatch in 52–59 days under the conditions stated above.

5. The larvae gorge for 3–6 days, the majority becoming replete on the third and fourth days after attachment.

6. The metamorphosis of the larva is prolonged by cold conditions and is hastened during warm weather. In a saturated atmosphere at 15, 20, 22 and 25° C., the mean times for moulting are respectively 60, 33, 27 and 23 days.

7. The nymphs gorge for 5–7 days, the greater number dropping off between the sixth and seventh days.

8. At 18° C. and 100% R. H. moulting of the nymph takes place about 32 days after repletion.

9. After metamorphosis the adults rest for 8–12 days, and feeding lasts 8–16 days.