In the last twenty-five years, since it was realized that the control of flock infections was more important than the treatment of individuals with patent infections, there has been an increasing interest in the use of anthelmintic drugs. As might be expected there has been a wide search for the most effective chemicals and considerable research into the best methods of administration, and as a consequence of this many workers have been engaged in devising methods of testing the efficiency of various compounds.

In a previous paper (Crofton, 1954) it was shown that the rise in egg counts occurring in ewe flocks in spring was related to the time of lambing. It was further shown that the rise in individuals occurred about 6 weeks after parturition and was normally of short duration. While the mean time of increased egg count for each individual was about 2 weeks, the increased egg count in the flock was spread over a period equivalent to the length of the lambing period. It is clear that the apparent rise in the flock as a whole will be greatest when all the flock lambs within a short period. With greater scatter of times of parturition the flock rise will be smaller but will extend over a greater period. This association of rise in egg count with time of parturition is obviously one of considerable selective advantage, in so far as an increase in infective stages will occur at a time when the susceptible lambs have a reduced milk intake and an increased grass intake. The synchronization of availability of infective stages and the occurrence of susceptible individuals is further emphasized by the relation of the period of increase to the time of birth of the lambs, the duration of the period of increase in the flock being directly proportional to the duration of the lambing period. This type of ‘escapement’ control is seen in so many other host-parasite relationships that it makes considerable appeal on general grounds. Other workers, Morgan, Parnell & Rayski (1951), have, however, related the rise in egg counts to climatological factors, but climatic control would not give the close synchronization described above.

It is usual, when considering the trichostrongyle infections of sheep, to refer to parasitic stages in the host and free-living stages on pasture as two separate entities with ecological, structural and physiological differences emphasized by their temporal relationship. They are, however, interlinked phases in a continuous exchange process in which the host acts as a vehicle. The role of the host as a mediator in this exchange has received little attention until recently and has been mainly restricted to a more dynamic approach to problems of immunity. The behaviour of the host, as well as that of the parasite, is obviously of great importance, but there has been little work on the behaviour of sheep in relation to patterns of helminth infections, although Taylor (1954) discussed the problem in general terms.

1. Infestation of the kidney of M. sowerbii and A. reticulatus by unencysted brachylaemid metacercariae led to a widespread necrosis of the organ. The necrotic debris was ingested into the gut crura of the parasites.

2. M. sowerbii is considered to be a natural intermediate host of the parasite and A. reticulatus to be an unnatural host, because in A. reticulatus parasitization led to a host mortality closely related to the degree of infestation, whereas M. sowerbii withstood the damaging effects of parasitization until the parasites reached maturity.

3. In A. reticulatus the rate of ingestion of food and the rate of egg production were reduced during parasitization.

4. No further effects were observed in either host species.

5. The possibilities and difficulties of using unencysted metacercariae to control pests are discussed.

1. Cucumaricola notabilis, a new genus and species of Copepoda, occurs in cysts in the coelom of Cucumaria frauenfeldi Ludwig collected at Sea Point, Blaauwberg Strand and Dalebrook in the Cape Peninsula.

2. An account is given of the features of the sexually dimorphic males and females.

3. Fertilized eggs and nauplius larvae are also contained in the cysts and, from observations on living material, it has been established that, after escaping from the cysts, the larvae metamorphose within a short period into the copepodid stage. There are two copepodid stages, the first an active swimming form and the second a quiescent phase from which the juvenile parasite develops.

4. Although of uncertain systematic position, this parasite seems to be nearly related to the Chondracanthidae. This conclusion is based on the similarity of the trunk appendages of the adult female to those of Acanthochondria as described by Oakley (1930), and also on the general agreement of the ontogeny with that of Acanthochondria cornuta investigated by Heegaard in 1947. It is further suggested that it may be assigned to the key devised by Delamare Deboutteville & Nunes-Ruivo (1955) for certain copepod parasites having some affinity with the Chondracanthidae.

The occurrence of Globidium gilruthi in sheep and goats in Egypt is recorded. Preliminary investigation showed that 18 % of 250 sheep and 28 % of 150 goats were infected. The lesions caused by G. gilruthi are described.

The stages of spermatogenesis and the structure of the primary oocyte of Sphaerostoma bramae were studied in material fixed in Bouin and Flemming's fluid and in preparations treated according to the Kolatchev and the Feulgen techniques.

Chromosome counts of primary and secondary spermatocytes indicate that the diploid number is twenty-four.

The stages of spermatogenesis, in general, conform to the usual pattern of this process in digenetic trematodes. The spermatogonia, spermatocytes and early spermatids are not connected together by central strands, nor by a central disk, as is claimed for some other species. A study of sections stained in haematoxylin and of Feulgen preparations showed that the spermatozoon is composed of an elongate nucleus and a tail. It was not possible, with the methods employed during the present investigation, to determine the fine structure of the tail.

The primary ovarian oocytes are in the interphase or in early prophase of the first maturation division. There is evidence that material is extruded from the nucleus to the cytoplasm.

The Golgi elements of the male germ-cells are revealed in Kolatchev preparations as short rods and filaments. The Golgi elements of the spermatid are eliminated in the residual cytoplasm. Mitochondria, in the form of granular bodies and short rods, were visible in spermatogonia, spermatocytes and spermatids. Those of the spermatid remain in the residual cytoplasm.

Short, rod-like Golgi bodies are present in the primary oocytes. In the young cells they form a compact mass situated close to or in contact with the nuclear membrane. Later, the elements spread out through the cell. Granular and rod-shaped mitochondria are concentrated in a single mass at one pole of the nucleus or in two masses at opposite sides of the nucleus. A few mitochondria are scattered through the cytoplasm.

1. The parasitization of the slugs Milax sowerbii and Agriolimax reticulatus by a brachylaemid trematode in an area in Durham, during the period 1949–53, is described. Evidence is given that M. sowerbii is a natural intermediate host of the parasite.

2. Seasonal fluctuations in the incidence of infestation are described, including the fluctuations in the incidence of the four developmental stages of the metacercariae. Primary (spring) and secondary (autumnal) infestations of the molluscs are described.

3. The implications of an unexplained decline in parasite density during 1953 are noted.

4. A life history for the parasite, involving a small mammal as the vertebrate host, is postulated.

1. Cercaria X (Baylis & Taylor, 1930) and its sporocyst have been redescribed with some additions to the original descriptions.

2. The details of the development of the cercaria into a metacercaria of the diplostomulum type have been obtained and the anatomy of the mature metacercaria is described in detail for the first time. It is proposed to name the metacercaria Diplostomulum X. Development of the cercaria into a metacercaria takes from 40 to 90 days and the metacercariae have been shown to survive for a period of 544 days after the time of infection. This development has been obtained in the lenses of rats, frogs and a wide variety of fish. Development is not completed in any other region of the host's body.

3.The effect of the sporocyst, migration of the cercariae, and the metacercaria on the appropriate host tissues has been considered. All these stages produce extensive changes in the host tissues.

4. Histochemical tests have shown the presence of alkaline phosphatase activity in the cuticle of the sporocyst. The glycogen storage regions of the cercaria are described and it has been demonstrated that the caudal bodies in the tail-stem contain large amounts of glycogen which are utilized during the free-swimming period.

5. Attempts at the completion of the life cycle were unsuccessful.

1. Crepidostomum farionis (Müller, 1784) and C. metoecus (Braun, 1900) were found to occur together in the same host fish, Salmo trutta L., S. salar L. and Anguilla anguilla (L.) in mid-Wales. It is believed that the latter species constituted an accidental host.

2. C. metoecus is recorded in Britain for the first time.

3. There was some evidence of a habitat isolation in individual fish as C. metoecus occurred predominantly within the pyloric caeca, while C. farionis usually occupied a more posterior station in the intestine.

4. A detailed description is given of G. metoecus and the salient features of this species are compared with those of C. farionis.

5. The two species of Crepidostomum commonly occurred in large numbers in their fish hosts, individual fish harbouring up to 157 worms. No lesions attributable to Crepidostomum were, however, detected and there was no evidence of pathogenicity.

6. It would appear that the eel is physiologically immune to both species of Crepidostomum and that the salmon parr is partially resistant.

7. The degree of infestation of trout and parr with both the Crepidostomum species is at a maximum during the winter months and at a minimum in the summer months. This seasonal variation can be attributed to a periodicity in the swarming of the cercariae.

8. There is no evidence of age resistance or acquired immunity of the trout to infestation by Crepidostomum species.

Components of the intricate ked-sheep pattern, of significance in dissemination of the ked, are defined. It was found that the dissemination potential (percentage of population on the fleece surface) on one sheep was constantly greater than on a second. Bright sunshine caused an increase in the dissemination potential, particularly on the first sheep. It was concluded that the stimulating factor was a rise in the fleece temperature in regions directly exposed to the rays of the sun.

The factor or factors causing differences in dissemination potential arose from similar degrees of temperature change being superimposed on inherently different fleeces. The sexes behaved similarly on both sheep.

Keds were able to transfer readily between the two sheep. However, when they were concentrated on the sheep with a high dissemination potential, the population of the two-sheep system declined rapidly; when they were placed on the sheep with a low dissemination potential, the population of the two-sheep system increased. Approximately half of the keds leaving the sheep with a high dissemination potential did not reach a second host. It thus acted as a disinfecting agent.

Bird and host predation were discounted as factors in causing ked population change.

The daily rate at which a young lamb acquired keds from its mother was studied. Keds applied themselves closely to the skin of the lamb, many on the under, sheltered parts of the body. It is concluded that there was almost completely oneway traffic of keds from the ewe to the lamb. A fall in the rate of transfer of keds to the lamb was attributed to declining frequency of contact between the latter and its mother, associated with transition from a wholly milk diet to one in which pasture became of increasing importance. It was found that during the hours of darkness and some hours of daylight few, if any, keds were acquired by the lamb. Keds tended to accumulate on the lamb in greater numbers during periods of many hours of bright sunshine and little rain than those of few hours of sunshine and much rain. The running totals of keds acquired by the lamb more nearly paralleled the running totals of hours of bright sunshine than other meteorological factors. It is concluded that the connexion was indirect and that sunshine raised the temperature of the fleece of the mother in the regions directly exposed to the rays, causing greater numbers of keds to appear on the surface, so that the lamb was exposed to a risk of heavier infestation. At one stage of the experiment a greater proportion of the males than females transferred from the ewe to the lamb. This is explained in terms of there being a higher proportion of males in the hinder part of the body of the ewe, a region with which the lamb, in feeding, came more frequently into contact. The higher ratio of males to females in the posterior half of the lamb than in the anterior is explained by the more pronounced habit of males than females to migrate through the fleece.

A new schizogregarine Mattesia orchopiae, n.sp., parasitic in the flea Orchopeas wickhami, is described. The schizogony takes place in the fat-cells, while the gametogony and the sporogony occur in the Malpighian tubules. The micronuclear schizonts measured 13·7 × 11 μ. The trophozoites of the second schizogony measured 14·2 × 3·5 μ. The spores measured 10·5 × 7 μ.

After staining with toluidene blue metachromatic granules were found in the cytoplasm of the macronuclear schizonts and in the merozoites and the trophozoites resulting therefrom. Some of this metachromatic material could be removed by digestion with ribonuclease, while the rest of it persisted. Material stained with alcian blue was detected in the cytoplasm of the macronuclear schizonts.

I wish to thank Professor P. C. C. Garnham for encouragement and advice received during the conduct of this investigation, Mrs M. Vizoso and Miss K. Meedeniya for the supply of the fleas, the authorities of the British Museum for the identification of the fleas, and Sir W. P. MacArthur for his advice regarding the problem of nomenclature.

Approximately 5000 birds (78 species) were trapped on Fair Isle and examined for fleas. Six species of flea were recorded: D. g. gallinulae (430 records), C. gallinae (205 records), C. borealis (126 records), C. garei (4 records), C. fringillae and C. vagabundus (1 record each).

The infestation rate among spring-passage migrants was 52·2% and among autumn-passage migrants only 2·7%. Spring migrants released and retrapped after ‘de-fleaing’ in the Fair Isle apparatus showed a 55% re-infestation rate. On spring migrants D. g. gallinulae was the dominant flea, but on autumn migrants C. gallinae was dominant. The most heavily infested group of birds were the Turdidae (61% spring, 3% autumn infestation rate) and Sylviidae (53% spring, 1% autumn infestation rate).

A number of double and triple infestations with 2 or 3 species of flea is recorded. Double infestations involving D. g. gallinulae and C. borealis occur more frequently than would be expected for purely chance associations. More male birds (90) than female birds (70) were infested.

The sex ratio of the fleas (on the bodies of birds) was: D. g. gallinulae 294 males, 325 females; C. gallinae 115 males, 214 females; C. borealis 77 males, 77 females. On the spring migrants there was an excess of male D. g. gallinulae and on the autumn migrants an excess of females.

On the resident birds there was definite evidence of host preference. The starling was the chief host of C. gallinae, the pipits of D. g. gallinulae and the wheatear of C. borealis. The re-infestation rate of ‘de-fleaed’ retraps showed a higher rate than original trappings in all cases, but the lack of D. g. gallinulae on retrapped starlings suggested some host selection on the part of the flea.

The proportions of the three principal species of flea found in (i) the nest of the wheatear, and (ii) on the body of the bird were strikingly different.

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.

A description is given of the stages of sporogony of Hepatozoon sciuri, which have been found in three wild fleas (Orchopeas wickhami) out of a total of nearly sixty specimens collected from squirrels in England. Although an attempt to infect the fleas in the laboratory, by feeding them on infected squirrels, failed, the above findings indicate that these fleas may act as vectors of the squirrel parasite.

We wish to record our thanks to Professor P. C. C. Garnham for his kind interest and constructive suggestions regarding this work. We are specially indebted to Mrs M. Vizoso and to Dr J. F. D. Frazer for sending us fleas and squirrels from time to time. Our thanks are due to the authorities of the British Museum of Natural History for the identification of the flea.

1. Axenic strains of Entamoeba invadens can be maintained indefinitely, by serial culture, in saline containing a slice of liver. Growth in this medium is poor, the amoebae are vacuolated, and few cysts are formed.

2. The optimum concentration of NaCl for amoebic growth in this medium is 0·75–1·0%, and the optimum pH is 5·7–6·1.

3. The source of the liver tissue in the medium is unimportant, but, of several tissues tested, liver was the only one which supported amoebic growth in serial culture.

4. Suspensions of minced liver also supported amoebic growth, but the growth-promoting activity of the liver was removed completely by centrifugation, autoclaving, and Seitz- or glass-filtration. Heat treatment at 50–60° C. and prolonged storage at 8° C. partially inactivated the liver.

5. Growth in axenic saline-liver medium does not affect the ability of E. invadens to grow and undergo mass encystation when reassociated with suitable bacteria.

The male, female and fourth-stage larva (female) of Hammerschmidtiella diesingi are described. Characters are given by which this species can be identified from the female fourth-stage larva.

A constriction and ring of clear cells separate the intestine of the male and of the female fourth-stage larva into two parts, and descriptions of the structure and mode of action of this ‘sphincter’ are given.

This work was carried out during the tenure of a Research Studentship awarded by the Department of Scientific and Industrial Research.

1. A study of the digestive enzymes present in the nematode Leidynema appendiculata, parasitic in the cockroach, gave the following results.

2. An amylase with optimum activity at pH 4·5, is present. Sodium chloride increases activity by 29 % at this pH.

3. A maltase, with maximum activity at pH 5·0–6·0, is present. It is completely inhibited by 15 % glycerin.

4. Lactase and invertase were not detected.

5. A protease, capable of clotting calcified milk, and of splitting gelatin and edestin, with maximum activity at pH 6·0, is present. KCN does not increase activity.

6. Peptidases splitting glycyl-glycine, dl-leucyl-glycine and dl-leucyl-glycyl-glycine, and a prolidase splitting glycyl-l-proline are present.

7. A lipase hydrolysing glycerol tributyrate, with maximum activity at pH 7·0 is present. Hydrolysis of olive oil and ethyl butyrate was not detected.

8. It is concluded that these enzymes are quite distinct from those of the host and that digestion probably takes place over the range of pH 5·5–6·0.

1. Evidence is produced to show that the larvae of Gasterophilus intestinalis are occasional blood feeders but normally feed on tissue exudate.

2. The demonstration, by Roy (1937), of the following enzymes has been confirmed and curves of their activity at different hydrogen-ion concentrations have been constructed: mid-gut amylase, proteinase and lipase.

3. The following enzymes have been demonstrated and curves of their activity at different hydrogen-ion concentrations have been obtained: maltase, invertase, polypeptidase and di-peptidase of the mid-gut and amylase, maltase and invertase of the salivary glands.

4. The haemolymph was shown to contain a lipase as well as an amylase and an anticoagulin.