Showing papers in "Parasitology in 1970"

A field study of nematode parasite populations in the lactating ewe.

Abstract: A typical postparturient rise of parasite egg output occurred in a group of lactating ewes. At parturition these animals carried few inhibited fourth-stage larvae and the rise was associated with a net increase in parasite populations, which did not occur in non-lactating ewes. Lactating ewes whose established parasite populations were effectively removed just prior to parturition showed a similar rise derived entirely from infection acquired during lactation, which was of much greater magnitude than that seen in similarly treated non-lactating animals. Circumstantial evidence of increased fecundity of T. colubriformis females in lactating ewes was also obtained.It was concluded that the postparturient rise of egg output may derive from an increase in adult parasite populations by an increased rate of establishment of newly ingested infective larvae which develop to the adult stage without inhibition, as well as by the resumption of development of previously inhibited fourth-stage larvae. In addition, both newly acquired and established adult female parasites may show increased fecundity.Ewes whose lambs were removed at birth or after a period of lactation showed a rapid fall in faecal egg counts associated with rejection of part of their existing worm burden and a pronounced increase in resistance to new infection.All of the differences observed between lactating and non-lactating ewes in the behaviour of their parasite populations were found to be qualitatively the same as those that have been frequently reported in susceptible and resistant non-reproductive sheep. The hypothesis is suggested, therefore, that the postparturient rise derives from a pronounced but temporary relaxation of immunological control of gastro-intestinal nematode infection associated with the endocrine status of the lactating ewe.

The regulation of populations of Ostertagia ostertagi in calves

Abstract: The course of the worm burdens of calves infected daily with larvae of Ostertagia ostertagi at five different rates was studied by making post-mortem worm counts on groups of calves killed after experiencing infection for different periods of time.The relationship between worm numbers and infection rates together with evidence that a turnover of worms occurred, led to the conclusion that burdens of adult worms were regulated primarily by a loss of worms at a rate proportional to the number present.Further, estimates based on the number of developing fourth-stage larvae indicated that the proportion of the larvae administered which became established decreased gradually as the experiment progressed.At very low infection rates, the rate of turnover of the worms was slower than at high infection rates but in all groups it remained constant through the 6 months duration of the experiment.The development of a small proportion of the larvae administered was arrested at the early fourth stage. At the highest infection rate used, the proportion of worms that became inhibited was somewhat greater.

In vitro cultivation of Echinococcus granulosus, Taenia hydatigena, T. ovis, T. pisiformis and T. serialis from oncosphere to cystic larva

Abstract: A technique for the hatching and subsequent in vitro cultivation of the oncospheres of Echinococcus granulosus, Taenia hydatigena, T. ovis, T. pisiformis and T. serialis to cystic larvae is described. The cytology and histology of developing larvae were also studied.The basic culture medium consisted of medium 858 containing additional glucose and K+ supplemented with the appropriate host sera. Fresh sera from young animals was generally more successful in promoting growth than sera from commercial sources. Cultivation was carried out at 37°C in roller tubes with a gas phase of 10% O2+5% CO2 in N2.The most successful results were obtained with T. pisiformis, oncospheres of which were grown to the cystic stage with development of hooks and suckers. During the later culture period, the bladder, although morphologically normal, ‘collapsed’ and did not retain its cystic shape.In culture, larvae of T. pisiformis became motile at 3 days and at 5 days began secreting droplets from a glandular apical region; this region stained differentially in alcian blue.Some larvae of T. pisiformis showed a tendency to undergo transverse or longitudinal fission, an effect possibly associated with the centrifugation applied during the early cultivation procedures.Early cystic development was obtained with the other species studied, but experiments carried out were only of a preliminary nature. However, the development rate in these experiments approximated that recorded in vivo.

The fine structure and function of the adult epidermis of two skin parasitic monogeneans, Entobdella soleae and Acanthocotyle elegans.

Abstract: Electron-microscope investigations on the outer layers of parasitic platyhel-minths have so far neglected the monogeneans and have been confined to the endoparasitic digeneans and cestodes (Braten, 1968; Burton, 1966; Charles & Orr, 1968; Erasmus, 1967; Lumsden, 1966; Morris & Threadgold, 1967; Race, Larsh, Esch & Martin, 1965; Rothman, 1968; Threadgold, 1965). For this reason the covering layer of monogeneans is still referred to as a ‘cuticle’ even though it is unlikely to be so since the surface of the endoparasitic platyhelminths has been shown to be a living cytoplasmic ‘epidermis’ (see Lee, 1966) which, as pointed out by Erasmus (1967) and Lumsden (1966), constitutes a metabolically active inter-face with host tissues and fluids. Two main considerations prompted the present investigations of the covering layer of monogeneans. First, it was hoped that a comparison of the covering layer of these ectoparasites with that of the digeneans and cestodes might help to define particular specializations of this layer associated specifically with the ectoparasitic or endoparasitic habit; secondly, because ectoparasitism can, in an evolutionary sense, be considered as a transitional state between a free-living and an endoparasitic existence (see Llewellyn, 1965), it was felt that this work on monogeneans could assist an understanding of the evolution of the platyhelminth outer layer.

Changes in body weight and intestinal absorption during infections with Eimeria acervulina in the chicken.

Abstract: Heavy infections of E. acervulina result in a depression in body weight of the host, but anorexia induced by the disease is not the only factor responsible for this, since normal birds starved to the same extent did not lose as much weight. It was shown that the absorption of l-histidine and glucose from the infected part of the small intestine was depressed and may be a contributory factor to this weight loss; restricted feed intake alone tended to increase, rather than decrease, absorption.

Observations on the epidermis of the miracidium and on the formation of the tegument of the sporocyst of Fasciola hepatica

Abstract: The relationship between the ciliated epidermal cells and the subepidermal layer of the miracidium of Fasciola hepatica has been described. Non-ciliated ridge-like extensions of the subepidermal layer separate the ciliated epidermal cells from each other. The sunken portions of the subepidermal layer, each containing a nucleus, lie below the outer body wall muscles of the miracidium and open into the ridge by narrow neck-like connexions. Elongate vesicles, which may be a source of stored plasma membrane similar to that which occurs in the transitional epithelium of other animals, fill most of the ridge. In addition, characteristic round electron dense granules are found in the ridge but the majority are found in the sunken portions of the subepidermal layer.The development and origins of the tegument of the sporocyst of F. hepatica have been described at the ultrastructural level. When the miracidium is in the process of penetrating the snail host, large vacuoles appear between the ciliated epidermal cells and the basal lamina which overlies the muscles of the body wall. These vacuoles have the effect of loosening the epidermal cells from the basal lamina of the body wall of the miracidium. Possible mechanisms involved in the formation of such vacuoles are suggested and discussed.During penetration of the snail the ciliated epidermal cells of the miracidium are lost; the ridge, a syncytial layer between the epidermal cells which is connected with the subepidermal layer, spreads over the basal lamina and exposed body wall muscles of the metamorphosing sporocyst to form the new outer covering of the sporocyst.Cytoplasm passes from the subtegumentary layer into the tegument during this stage of the development of the body wall of the sporocyst. Muscular contraction and microtubules may be involved in the outward movements of this cytoplasm. The nuclei of the subtegumentary layer remain below the muscles of the body wall.Twenty-four hours after penetration of the snail the outer plasma membrane of the tegument forms folds, which greatly increase the surface area.Sixty hours after penetration involutions between the folds, which may indicate pinocytosis, are present, and it is suggested that pinocytosis may play a role in food absorption.The fully formed tegument is a syncytial layer containing numerous electron dense granules, vacuoles, mitochondria and lipid droplets.The results on the formation of the tegument of the sporocyst have been discussed with reference to the controversy about the origins and terminology of the outer covering of the Platyhelminths.

The response to desiccation of eggs of Trichostrongylus colubriformis and Haemonchus contortus (Nematoda: Trichostrongylidae).

Abstract: Eggs of T. colubriformis and H. contortus were separated from faeces. Their response to desiccation was compared by subjecting them, at different stages of development, to a range of relative humidities. Many eggs of T. colubriformis at all stages of development survived desiccation at relative humidities down to 75%, whereas the only H. contortus eggs to survive were those exposed to the highest relative humidity and which had already undergone a substantial amount of development before desiccation.

Extended schizogony of Eimeria mivati in betamethasone-treated chickens

Abstract: Cortisone treatment of BL chickens given oocysts of Eimeria mivati resulted in the production of greater numbers of oocysts in the faeces and a prolonged patent period.Schizonts were seen in sections of the intestines of treated birds up to the 24th day after oocyst inoculation although none was seen in control chickens after the 8th day. These late schizonts resembled those of the 3rd and 4th generations recorded for this species but may be those of a generation not yet described.The depletion of intestinal lymphoid tissue in cortisone-treated birds is noted. The findings are discussed with reference to host-parasite relationships.We wish to thank the scientific assistants and senior poultry attendant of the department for their help throughout the work.

The production, transfer and assimilation of spermatophores by Entobdella soleae, a monogenean skin parasite of the common sole.

Abstract: It has been shown that mating involving mutual exchange of spermatophores takes place in the skin-parasitic monogenean Entobdella soleae from Solea solea. The spermatophores are attached to the ventral surface of the body in the region of the vaginal opening and they are sucked into the vagina after mating by muscular contractions of the vaginal region.Mating takes place between young individuals with no vitellaria and between fully mature egg-laying adults but there is no evidence that self-fertilization takes place.The apparatus which manufactures the spermatophores is described and the evidence indicates that spermatozoa are injected into the jelly-like matrix of the spermatophore as the matrix is being extruded into the surrounding sea-water.I would like to thank the Director and Staff of the Laboratory of the Marine Biological Association at Plymouth for providing excellent facilities for this work and I am particularly grateful to Mr J. E. Green, who kindly fed and maintained infected soles at the Laboratory.

The life cycle of Basilia hispida Theodor 1967 (Diptera: Nycteribiidae) in Malaysia*

Abstract: Basilia hispida is the only insect parasite of the flat-headed bats Tylonycteris pachypus and T. robustula in Selangor, Malaysia where this study was conducted between September 1966 and August 1968. The climatic conditions in the laboratory closely approximated to those in the field: seasonal variations in climate were small but diurnal fluctuations occurred. The life cycle of the fly was not affected either by the season or by the sex or species of the host.A typical life cycle was as follows: adult B. hispida reached sexual maturity within 5 or 6 days of their emergence from the puparium. Copulation largely occurred with newly emerged flies or with females at the time of prepupal deposition; one copulation sufficed for numerous subsequent offspring. The entire larval life of three instars was passed within the female, nourished by maternal secretions. After reaching maturity the female deposited prepupae at 9-day-intervals on the host's roosting quarters, deposition occurring during the day, stimulated by increasing temperature. The length of the pupal stadium depended upon the presence of a host bat; if one was present the pupal period was ca. 25 days. Thus the total life cycle from emergence of the female to the emergence of her first offspring was typically 39 (5 + 9 + 25) days. The sexes were produced in equal numbers. The greater part of postembryonic mortality occurred in the adult instar and was largely due to host-predation. Females were longer lived than males, and it was suggested that they had an average life expectancy of 5–6 weeks in the field.The life cycle of five other species of Nycteribiidae from two other species of host were briefly examined and no major differences from B. hispida were noted. The results of this and of previous studies indicate that the life cycle is fairly uniform throughout the family.

"Host" antigens associated with schistosomes: observations on their attachment and their nature.

Abstract: Further investigations have been carried out on the nature of ‘host’ antigens associated with the adult worms of Schistosoma mansoni These investigations show:1 The ‘host’ antigens are not removed from the surface of the worms by thorough washing and prolonged incubation in Hanks's balanced salts solution The antigens must be firmly bound or even incorporated at the surface2 Monkeys cannot be immunized against ‘mouse worms’ with mouse IgG immunoglobulins Accordingly it is unlikely that the ‘host’ antigens are mouse anti-worm antibodies3 The ‘host’ antigens are certainly associated with the membranes of mouse erythrocytes They may also be associated with the ‘soluble protein’ fraction of the erythrocytes4 Immunization with sheep erythrocytes failed to protect monkeys against challenge with ‘mouse’ worms Therefore it is unlikely that the ‘host’ antigens are Forssman antigen5 The mouse ‘host’ antigens associated with ‘mouse’ worms are not major histocompatibility antigens Consequently it is likely that they are species-specific mouse antigens

Some factors affecting the severity of infection with Eimeria tenella in chicken embryos.

Abstract: Some factors affecting the suceptibility of chick embryos to E. tenella infection have been examined. An incubation temperature of 41 °C was found to be more suitable for the development of the parasite than 38 or 39 °C. At the higher temperature development of schizonts was more rapid and mortality caused by the parasite occurred earlier and was substantially greater. Mortality, caused by E. tenella, was dose related and doses between 15000 and 45000 sporozoites produced 100 % mortality in embryos incubated at 41 °C.There were differences in the susceptibility of three strains of W.L. embryos to E. tenella infection; ‘S’ strain W.L. embryos were more susceptible than either ‘C’ or ‘K’ strains. However, the susceptibility was not evident in hatched chickens of the ‘S’ strain.Two laboratory strains of E. tenella (‘W’, ‘H’) were shown to produce different mortality levels in embryos; the ‘W’ strain was markedly more virulent, perhaps because schizonts of the 2nd generation matured more rapidly in both embryos and chickens inoculated with this strain of E. tenella.I wish to thank Dr R. K. Cole of Cornell University for making three strains of W.L. embryos available to me for this work. I also wish to thank the Governing Body of the Houghton Poultry Research Station; the Agricultural Research Council and the Avian Diseases Department of Cornell University for making it possible for me to undertake a substantial part of this work at that University in 1968. Grateful thanks are due to Dr P. P. Levine, D. L'Amoreaux and M. S. Shirley for their help at various stages of the work.

The development of Echinococcus granulosus larvae in laboratory animals.

Abstract: Rabbits and mice, but not sheep, guinea-pigs or rats, were suitable hosts for secondary echinococcosis using protoscoleces obtained from Australian sheep. The host specificity is tentatively related to the phylogenetic relationship between the donor host and receptor host.The development rate of hydatid cysts in mice is described in terms of increase in fresh weight, dry weight, and maximum cyst diameter. Fertile cysts were found after 8 months when the water content of the cysts had increased to more than 95 %. The diameter of fertile cysts up to 14 months ranged from 6 to 30 mm. By 14 months, the average fresh weight of cysts was greater than the body weight of the mice.This work was carried out during the tenure of an Australian Wool Board Senior Postgraduate Scholarship, and forms part of a thesis to be presented for the degree of Doctor of Philosophy of the Australian National University.I wish to thank my supervisor, Professor J. D. Smyth, for guidance and criticism.

A morphological and histochemical study of Trichuris suis (Schrank, 1788) with special reference to the host-parasite relationship

Abstract: Adult forms of the pig whipworm, T. suis, are able to establish intimate contact with the host's tissues by the formation of a tunnel-like construction which covers a section of the thread-like oesophageal region. The extreme anterior oral end and the stouter posterior region are not covered and lie free in the lumen of the caecum. The attachment tunnel is composed of host mucosal cells and goblet cell secretion and its possible mode of construction is discussed. Host tissue not directly involved in tunnel formation appears unharmed by the presence of the parasite. T. suis is therefore not a serious pathogen under natural conditions.It has been demonstrated that characteristic structures of the trichuroid oesophageal region, e.g. bacillary band and stichosome are metabolically active. The former penetrates the layered cuticle in the form of columnar protrusions originating in the hypodermis. Each hypodermal column represents a gland cell or bacifiary cell, which displays enzymic activity, e.g. acid phosphatase, non-specific esterase, glucose-6-phosphatase, succinate dehydrogenase, cytochrome oxidase and β-d-glucosidase. Its possible function at the host-parasite interface and in the metabolism of the whipworm is discussed. The layered cuticle is proteinaceous and enzymically inert.Glandular activity is also displayed by the stichosome surrounding the capillary-like oesophagus. This evidence confirms earlier suggestions that the stichosome is a series of oesophageal glands.Although the bacillary band may be involved in nutrient uptake the evidence obtained indicates that this is via the mouth which is favourably placed for the ingestion of mucoid material which was detected in the oesophagus. This may be subjected to preliminary hydrolysis by the enzymes present in the oesophagus and stichosome.

Nematode parasites of Oceanica. IX. Capillariids from passeriform hosts collected in Taiwan.

Abstract: The capillariid nematodes present in passeriform hosts collected in Taiwan are recorded and described. Two new species are established, Capillaria parusi sp.n. from Parus monticolus insperatus and Sitta europaea formosana , and C. madseni sp.n. from Corvus macrorhynchus colonorum , and their affinities are discussed. Capillaria tridens, C. longifila and C. contorta are recorded from a number of new hosts.

The excretory metabolism of the endoparasitic digenean Fasciola hepatica and its relationship to its respiratory metabolism.

Abstract: The amounts of ammonia excreted by two endoparasitic flatworms have been compared and, weight for weight, the sheep liver fluke Fasciola hepatica produces ten times as much ammonia as the rat tapeworm Hymenolepis diminuta . This is thought to reflect a difference in diet, the fluke feeding mainly on the blood and tissue proteins of its host, and the tapeworm mainly on carbohydrates from the food materials in the gut of the host. However, the addition of glucose to the saline in which the flukes are cultured produces a marked decrease in the ammonia and an increase in the lactic acid excreted, suggesting that flukes are not obligatory protein feeders but that they may utilize carbohydrate when it is available. The relatively low production of lactic acid when proteins are being metabolized suggests that the flukes are producing an alternative end-product of respiratory metabolism. It is possible that this is the neutral lipid found in the excretory system of Fasciola and the possibility of an alternative metabolic pathway for the production of such lipid is discussed. The respiratory metabolism appears to be independent of oxygen, and the possible role of oxygen in other aspects of the metabolism of the fluke is discussed. I should like to express my sincere gratitude to Dr J. Llewellyn for his constant advice and encouragement during the course of this work and the preparation of the manuscript. I also thank Professor 0. E. Lowenstein, F.R.S., for allowing me the use of the facilities in his department during the tenure of an S.R.C. Research Studentship. Finally, my thanks are due to Mr E. Wilson, the Veterinary Officer at the Birmingham City Meat Market, for his constant co-operation in obtaining supplies of liver flukes.

Some helminth parasites of fishes of Bermuda and an account of the attachment organ of Alcicornis carangis MacCallum, 1917 (Digenea: Bucephalidae).

Abstract: Of 414 Bermuda fishes, 148 belonging to 13 species harboured Digenea and 11 belonging to 6 species Aspidogastrea, Acanthocephala or nematodes. In a previous paper 69 of these fishes belonging to 20 species were found to contain cestodes. The number of infected species was greatest in the case of cestodes and the number of infected individuals in the case of Digenea. The latter is probably due to the closer proximity, for reasonably long periods, of the various hosts in the life-cycles. Of the 17 species of Digenea 3 are new host records, 3 new locality records and 4 new host and new locality records. New records were found, also, in the other groups of helminths. The digenean fauna of Bermuda fishes most closely resembles that of Dry Tortugas, Florida. Digenea and cestodes were not usually found in the same families of fishes. Cestode larvae were abundant in the deep-water Serranidae and Lutianidae which had no Digenea, the latter being common in Clupeidae, Hae-mulidae and Belonidae, which do not harbour cestodes and which occur, mostly, in the inner reefs and shallows.The functional morphology of the apical disk, tentacles and rhynchus of Alcicornis carangis is described. The tentacles are invaginable and concerned with attachment.I am most grateful to Dr W. H. Sutcliffe Jun., Director of the Bermuda Biological Station, for the excellent facilities provided and to The Shell Grants Committee and The National Science Foundation for grants which made the work possible. I would also like to express my gratitude to all those who kindly helped in the capture of fishes and to Mrs M. Fisher for technical assistance.

Diurnal movement of Hymenolepis diminuta in the rat

Abstract: Following a 2–5 ml meal containing 2 g (80%) glucose and 30 mg methionine administered by stomach tube at 09.00 h, H. diminuta was found to change its position in the rat's intestine. Usually while the stomach contained food ≤ 45 %, by weight, of the tapeworm lay in the posterior 40 % of the small intestine, after the stomach was empty the reverse was true.The effect of hyperosmotic fluid entering the duodenum was determined by injecting, following laparotomy, varying amounts of 80 % glucose and 1 ml of varying concentrations. A volume ≤ 0-4 ml of 80 % led to the death and expulsion of worms within 7 h, and 1 ml of < 50 % glucose also killed the worms.The expulsion of 15 % of the tapeworms from rats given 2–5 ml hypertonic meal by mouth was correlated with the failure of the stomach in some rats to regulate the stomach emptying. Worms in these rats were found from 4 h onwards in the caecum and large intestine, and by 9 h in the faeces.That the movement of worms, other than those expelled, was not caused by a sub-lethal flux of hyperosmotic fluid was shown by feeding an iso-osmotic meal to rats; the worms moved to a more posterior position during the day, but none was expelled.Single worm infections in rats kept on a normal feeding regime until 07.00 h and then starved throughout the day also showed a posterior migration. Using a method which involved the simultaneous cutting of the small intestine into 5 cm sections, it was possible to show that this movement involved the whole worm, the scolex moving from a mean position 10–15 cm to one 20–25 cm from the stomach, and the terminal proglottid moving from approximately 75 cm to 95 cm from the stomach.Worms in Wistar rats responded similarly to those in SPF CFE (Sprague Dawleys) with the exception that there was some evidence that the stomach emptying of a hyperosmotic meal was better controlled and hence a smaller percentage of the worms were expelled.The results are discussed in relation to diurnal changes in the level of the external site location stimulus which other workers have shown to exist by surgically transplanting H. diminuta into the ileum.The enthusiastic assistance of Miss Helen Stallard, B.Sc., and Miss Patricia Grant is gratefully acknowledged, and financial support from the Medical Research Council, London (Grant No. G967/164/T).

The effect of host lactation on the self-cure of Nippostrongylus brasiliensis in rats.

Abstract: The primary infection of breeding female rates with N. brasiliensis was examined as an experimental model for the study of the effect of lactation on host-parasite relationships. Self-cure was inhibited when the period of infection corresponded with lactation, and a majority of worms could persist to day 34 when lactation was prolonged. A normal self-cure occurred during pregnancy, when litters were removed at birth or when the suckling litter was reduced to 3 young.

Studies on the structure and hatching of the eggs of Schistosoma mansoni.

Abstract: The structure and function of the vacuoles in the eggs of Schistosoma mansoni is unknown. In this study the eggs have been immersed in serum albumin and examined by phase-contrast optics. Under these conditions the vacuoles exhibit a definite internal structure, suggesting that they may be or may have been cellular. Histochemical staining techniques to detect the nature of the vacuolar contents revealed that the vacuoles stained heavily with iodine and gave a positive PAS reaction. This suggested the presence of carbohydrate. Stains for nucleic acids, protein and lipid were not taken up by the vacuoles. The egg shell stained with o–toluidine blue and with basic fuchsin uniformly, except for a thin irregular band which might indicate a possible line of weakness. The vacuolar membranes seem to be similar to the vitelline membrane in permeability to hydroxyl ions and it is possible that these membranes have a common origin. Plasmolysis studies with salts, urea, glycerol and sucrose showed that the vacuolar membranes have about the same permeability properties to these compounds as the other egg membranes. Glycerol treatment of the eggs until equilibrium is attained, followed by transfer of the eggs to water or saline results in a hatching of the eggs. In this, a dead mira-cidium is extruded from the shell. Similar treatment of eggs equilibrated with sucrose does not result in this hatching process. It is postulated that glycerol solubilizes a factor which aids the hatching process.I should like to thank the following: Dr S. A. Ibrahim, in whose department this work was carried out; Dr S. Dawood of the Stack Laboratory, Khartoum, who kindly made his microscope available for use; Mr J. R. Lauder for valuable discussions and suggestions; and many young patients in Khartoum Civil Hospital for stool samples and smiles.

Studies on the distribution and site location of Nippostrongylus brasiliensis within the small intestine of laboratory rats.

Abstract: The distribution of N. brasiliensis within the small intestine of rats, following a primary infection, is described. The fourth stage larvae were found to inhabit the sections later parasitized by the adult population. Both the larval and adult worms were found to be confined to the anterior half of the small intestine. This aggregation is believed to be under the influence of stimuli (factor(s) 1), present in the lumen of the host gut. The adult worms also clumped within the already confined worm population. This behaviour is thought to be due to intrinsic behaviour patterns of the worm, sexual attraction and thigmokinesis. Larval and adult worms were surgically transferred to points, at varying distance from the ‘normally’ inhabited region, in the small intestine of fresh recipient rats. The resulting migratory behaviour of the worms was studied. The worm populations resulting from both the larval and the adult transfers showed the ability to recognize that they were in the wrong position of the small intestine and to be able to orientate, migrate and locate the ‘normal’ site.

The oncomiracidia of the monocotylid monogeneans Dictyocotyle coeliaca and Calicotyle kroyeri.

Abstract: The eggs of D. coeliaca have been cultured successfully and the free-swimming larva has been studied for the first time. The eggs have an incubation period which for monogeneans is exceptionally long (4–5 months at 10 °C). Apart from maintenance at a low temperature no other special conditions such as high hydrostatic pressure or washing to remove host body fluid are necessary for development. It is not necessary for the eggs to come into contact with host body fluid before development can begin. The oncomiracidium of D. coeliaca has no eyes, a well-developed pair of anterior median gland cells and a pair of hamuli. The oncomiracidium of C. kroyeri is similar to that of D. coeliaca except for the presence of two pairs of conspicuous pigmented eyes, poorly developed anterior median gland cells, the presence of an extra pair of gland cells at the posterior end of the body and the absence of hamuli. A comparison of the larval features of D. coeliaca and C. kroyeri has confirmed that these parasites belong to quite distinct species.

The host-parasite interface of strigeoid trematodes. IX. A probe and transmission electron microscope study of the tegument of Diplostomum phoxini Faust, 1918.

Abstract: A combined study using electron probe (Stereoscan) and transmission electron microscopy has revealed the existance of surface specialisation of the adhesive organ of adult Diplostomum phoxini Faust, 1918. The lateral walls of the adhesive organ bear stout spines, whereas the surface which comes into contact with the host tissues consists of numerous small chambers approximately 2 μ high and 0.5–1 μ in diameter. Within the chambers are slender microvilli. This surface is cytoplasmic and is in continuity with unicellular gland cells, lying within the body of the adhesive organ, via cytoplasmic processes. The chambered adhesive organ surface and the processes contain mitochondria, granular material and membrane bounded secretion bodies 0.18 μ in diameter containing densely staining granular contents. A fibrous basement layer is poorly developed and the basal plasma membrane of this surface is in close contact with adjacent parenchymal cells and the lacuna excretory system. Histochemistry has demonstrated the presence of non-specific acid phosphatase activity in the walls of the chambers, in the microvilli and in the cisternae of the gland cell endoplasmic reticulum. The gland cells contain extensive granular endoplasmic reticulum and numerous golgi complexes. The concept of surface specialisation in relation to function is discussed.

The distribution and fine structure of the integumentary papillae of the cercaria of Himasthla secunda (Nicoll).

Abstract: The distribution of the integumentary papillae of the cercaria of Himasthla secunda has been studied by a variety of techniques. Structures stained by silver nitrate and visible under the light microscope correspond in their spatial distribution with papillae observed under the scanning electron microscope. The tegumentary papillae described with the light and scanning electron microscope are correlated with the specialized nerve endings in the tegument as seen in transmission electron microscopy. The ultrastructure of these papillae is examined by conventional transmission electron microscopy and the probability that these structures are sensory is discussed.