A secretory cycle has been revealed in the intestinal epithelial cells of Fasciola hepatica. The basal regions of tall cells contain mitochondria-like bodies which stain deeply with basic dyes. These granules become numerous and are then arranged in vertical arrays of variable height which extend into the middle region of their cells. The distal halves of the epithelial cells contain numerous granules or droplets which have no affinity for basic stains and tend to swell, with consequent disarray of the secretory products. In the terminal parts of the cells vacuole-like formations appear, usually one to each cell, and eventually the lumen of the caecum becomes occluded by a froth-like mass of vacuoles. When food enters the caecum in small amount, the vacuoles are broken down and some secretion is liberated and mixed with the incoming homogenate. Meanwhile the vacuole-like structures encroach more deeply into the cell and eventually the residual secretion is discharged. New cell boundaries are being established near the nuclear zone and after complete discharge of secretion the distal parts of the cells consist of aggregates of long cytoplasmic filaments, which form a kind of fringe on the free borders of the now much shortened cells. These delicate cytoplasmic fringes, are abraded, probably by the physical action of streams of food, and typical short cells in caeca which contain food have much shorter fringes no more than one-half the height of the shallow cells. Ultimately all traces of such residual cytoplasm remaining after completion of the secretory cycle disappear. Short cells containing few granules are presumed to increase in height subsequently by regeneration of cytoplasm and, possibly, nuclear changes also, until they attain the form seen in cells commencing the secretory cycle. Such changes are especially difficult to observe because of variability in the heights of cells normally forming the epithelium. The especially tall cells which are seen, isolated or in small groups, at the height of the secretory cycle—the so-called pyramidal cells—are believed to be merely cells which have had their secretory activities delayed; ultimately, they are denuded in the same way as other cells during the secretory cycle. The type of secretory activity disclosed is therefore of the apocrine type, which is considered appropriate to the suctorial method of feeding employed by the fluke.

1. Frogs were collected from a single area in the West Riding of Yorkshire and examined for adult helminth parasites. The following species were found: Polystoma integerrimum, Gorgoderina vitelliloba, Haplometra cylindracea, Dolichosaccus rastellus, Rhabdias bufonis, Cosmocerca ornata, Oswaldocruzia filiformis, Aplectana acuminata and Acanthocephalus ranae.

2. The seasonal incidence and intensity of infection was studied by monthly examinations of 2413 frogs over a period of 4 years. The highest incidence of parasitization by helminths occurred in the autumn. In general, when the incidence was high, the intensity of infection was also high.

3. The incidence of infection was generally higher in male than in female frogs. This effect of the host's sex was much more marked immediately before the breeding season than at any other time of the year.

4. Possible reasons for these variations in levels of infection are discussed.

1. The development of resistance to proguanil and pyrimethamine was studied in a clone of Plasmodium gallinaceum (strain A) derived from a single erythrocytic parasite and maintained by a standard method of serial inoculations in young chicks.

2. The rate of the development of resistance to 0·05 mg./20 g. doses of proguanil was compared in strains maintained by inocula of 5 × 107, 108 and 109 parasites. Some evidence was obtained that the rate of the development of resistance to the drug was related to the numbers of parasites in the inocula.

3. No correlation was observed between the rate of the development of resistance to pyrimethamine and the size of the population of parasites exposed to its action in strains treated with 0·001 g./20 g. doses of the drug and maintained by inocula of 5 × 107 parasites or 109 parasites; but a greater variability was observed in the rate in the strains maintained by the small inocula than in the strains maintained by the large inocula. Resistance appeared to develop sporadically.

4. Some evidence was obtained that strains treated with a high dose of pyrimethamine (0·05 mg./20 g.) might become more sensitive to the drug as a result of treatment. In three experiments the infections were eradicated by the second or third course of treatment with the drug. However, strains which withstood this dose, developed resistance as rapidly, or more rapidly than those treated with 0·001 mg./20 g. doses. There was therefore no evidence from these experiments with pyrimethamine that resistance to the drug could be produced more readily with small than with large doses of the drug.

5. Except for slight variations, resistance to proguanil developed concurrently with resistance to pyrimethamine in strains treated with that drug.

6. In many of the strains, whether treated with proguanil or with pyrimethamine, resistance appeared to develop quite suddenly, but in others it developed more gradually. The pattern of the development of resistance in strains treated with either of these drugs could be explained by the selection of spontaneously occurring mutants, though some of the data suggested that the mutants differed in degree of resistance to the drug.

7. The rate of development of resistance to pyrimethamine was studied in strains derived from primary inocula composed of known numbers of pyrimethamine resistant parasites and 5 × 107 parasites of the untreated strain A. The addition of at least 106 resistant parasites to the inoculum was required to produce an increase in parasitaemia during the subsequent course of treatment with the drug, but the addition of 102 resistant parasites or, in some experiments, fewer than 102 resistant parasites to the primary inoculum was sufficient to produce a heavy parasitaemia during the second serial course of treatment if the strain was maintained by the standard method (p. 496). When these results are compared with the pattern of the development of resistance to pyrimethamine in the strains treated with that drug, it can be concluded that only in one strain was there any evidence that resistant parasites were present in the primary inoculum when it consisted only of parasites of the untreated parent strain. The rate of development of resistance in many of the strains treated with either proguanil or pyrimethamine suggested a mutation rate of a low frequency.

1. The pseudosuckers and holdfast organ of the metacercaria and adult stages of Diplostomum phoxini do not secrete acid mucopolysaccharide.

2. Alkaline phosphatase is present in the holdfast organ and in the cuticle lining the holdfast organ but not in the forebody glands or pseudosuckers.

3. Non-specific esterase has been shown to be present in the metacercaria and adult, especially in the pseudosuckers, the forebody glands which supply the pseudosuckers and in the holdfast organ. There is very little non-specific esterase in the posterior lobe of the adult.

4. Results of tests with enzyme inhibitors have shown that there are probably both A-esterase and B-esterase in the pseudosuckers, forebody glands and holdfast organ and that there is a cholinesterase present in the nervous system.

5. Cystine is present in most of the cuticle of the metacercaria but is absent from the cuticle lining the holdfast organ and the pseudosuckers.

6. The pseudosuckers and forebody glands as well as the holdfast organ appear to play a part in extracorporeal digestion.

1. The ecological relationships and life history of a Diplostomulum type of strigeid metacercaria encountered in several fresh-water fishes of Andhra Pradesh are described.

2. The development of the adult strigeid in the pond heron and cattle egret and structure and development of the miracidium have been traced.

3. The adult individuals are identical with Diplostomum ketupanensis Vidyarthi, 1937. It is suggested that D. heronei described by Srivastava (1954) may be a synonym of D. ketupanensis.

4. Attention is drawn to the possible relationship between D. heronei and the metacercaria Diplostomulum pigmentata Singh, 1956, which in its turn appears to be similar to the Diplostomulum in the present study.

We thank Sri S. Nagaraja Rao of Fisheries Department, Andhra Pradesh, for his kind help and co-operation.

1. Factors controlling the distribution of the bird fleas Ceratophyllus styx, the sand-martin flea, C. gallinae, the hen flea, and Dasypsylla gallinulae, the blackbird flea, were investigated in the field.

2. Sand-martin fleas (C. styx) pass the winter as adults within cocoons in the old nests of their host. Observations indicate that the fleas are stimulated to emerge from the cocoons by the rise in temperature in the spring, and some of the adult fleas emigrate in the spring and invade new nest burrows. Observations and experiments showed that sand-martin fleas disperse from old burrows both laterally and vertically and that emigrating fleas could reach areas as far as 33·8 m. from the old nests. The detection of the new burrow entrances is not due to vision, or to the recognition of difference of humidity between the burrow and the cliff face, or to the reaction to air current differences between the burrow and the cliff face, but to recognition of the horizontal floor of the burrows and a tendency to congregate upon horizontal surfaces. How the fleas distinguish the horizontal burrow surface from the cliff top is still unknown. The colonization of new burrows by the fleas does not occur at night. It is suggested that, in addition to finding their hosts in the spring by invading new burrows, sand-martin fleas may jump on to the birds when they are hovering near the cliff face. Many adult fleas leave the burrows within 3 days of the fledging time of the young sand-martins but a small number remain within the nest. The fate of these specimens is not known.

3. C. gallinae, the hen flea, and D. gallinulae, the blackbird flea, pass the winter principally as adults enclosed in the cocoons in the old nest material. In the spring they emerge from the cocoons, emigrate away from the old nest and are free-living on the ground. Probably the adult C. gallinae and D. gallinulae jump on to birds when they are feeding on the ground in the spring.* Therefore the absence of hen fleas in nests situated on the ground or in open nests built in low vegetation, is not due to lack of opportunity of contact between the adult flea and the birds which construct such nests.

4. It is concluded that in host-seeking, adults of C. gallinae and D. gallinulae emigrate away from old nests in the spring and come in contact with the host birds on the ground in the birds' feeding area, whereas C. styx adults emigrate into the hosts' breeding area and come in contact with the birds in the new nesting burrows.

1. The spermatophore of the argasid tick Argas persicus, is a sac enclosing a mass of sperm and a number of other structures which are rapidly extruded into the vagina of the female tick during copulation.

2. During copulation the first part of the contents of the spermatophore to be extruded consists of a clear tip with two lateral semi-opaque areas surrounded by white borders and a mass of opaque white material followed by the sperm.

3. The male accessory reproductive gland is redescribed. It consists of a stem portion which gives off: dorsally, the unpaired anterior dorsal granular lobe and the paired posterior dorsal and third lateral granular lobes; the small paired second lateral granular lobes from the mid-region; ventrally, the small unpaired median granular lobe and the large paired first lateral granular lobes and, opening into the ejaculatory duct, the small, paired anterior and posterior spongy lobes.

4. The anterior and posterior spongy lobes secrete an acid mucopolysaccharide which thinly coats the spermatophore.

5. The median granular lobe secretes a phospholipoprotein rich in phenolic groups and a polyphenol oxidase.

6. The first lateral granular lobes secrete a basic protein which interacts with the secretions of the median granular lobe to form the main wall of the spermatophore.

7. The second lateral granular lobes secrete the tenuous mucoprotein membrane which surrounds the sperm mass within the spermatophore and also the large protein granules which adhere to the inner surface of this membrane.

8. The third lateral granular lobe secretes the mass of opaque, white material in the spermatophore; possibly this is pharmacologically active and analogous to the secretion of the opaque glands of Rhodnius.

9. The posterior dorsal granular lobes secrete a non-specific esterase at their tip and a protein in the mid-region; these form, respectively, the lateral semi-opaque areas and their white borders in the spermatophore.

10. The anterior dorsal granular lobe secretes an acid mucopolysaccharideprotein complex which forms the clear tip of the extruded contents of the spermatophore.

Eperythrozoon teganodes is described from the blood of cattle. It is compared with, and is shown to be distinct from, E. wenyoni Adler & Ellenbogen, 1934. E. teganodes is a parasite of the plasma rather than of the erythrocyte. It occurs as fine rods and threads, rings, and rings with a rod or thread attached. (E. wenyoni adheres to the edge and the face of the erythrocyte, appearing as densely staining coccoids and faintly staining disks.) It is suggested that some highly polymorphic species of Eperythrozoon may prove to be a mixture of two or more species.

I wish to thank Professor J. F. A. Sprent for his advice and for criticizing the manuscript, and Messrs J. Ballantyne, C. Boel and F. Mellis for technical assistance. The photographs were taken by Mr E. Hollywood of the Photographic Department of the University of Queensland. I am grateful to Dr D. W. Brocklesby for allowing me to examine his material. This work was aided by facilities and funds provided by the Rural Credits Fund of the Reserve Bank of Australia, and by the Queensland Dairymen's Organization.

Paramphistomum daubneyi sp.nov., recovered from Bos taurus in Kenya, East Africa, is described and differentiated from the other species of the genus possessing a Microbothrium type of genital atrium.

Lymnaea truncatula Müller was infected experimentally with miracidia of P. daubneyi and the development in the snail host is briefly described.

1. Leucine aminopeptidase has been detected, histochemically, in the intestine, in the walls of the anterior part of the excretory canals and in the hypodermis of Ascaris lumbricoides.

2. The possible significance of leucine aminopeptidase in the walls of the excretory canal is discussed.

I wish to thank Dr Tate, in whose department this work was carried out, for his advice and encouragement during this investigation and Mr A. Page for technical assistance.

In a paper recently published (Lee, 1961) I described as new two species of freshwater nematodes. Since that paper was published my attention has been drawn to papers by Andrassy (1959, 1960) and Meyl (1957) and to the fact that I did not give a differential diagnosis, without which the specific names are not valid. The keys given by Thorne & Swanger (1936) and by Thorne (1939) were used initially to try to identify the specimens, which were compared with various species recorded up to 1956 in the Zoological Record. They have since been re-examined in the light of Andrassy's papers, (1959, 1960) and Meyl's (1957). Re-examination of the specimens showed that the guiding ring of Dorylaimus keilini is double (Fig. 1) and not single, as was originally figured (Lee, 1961).

There is histochemical evidence for the presence of calcium, glycogen, simple proteins and alkaline phosphatase in the calcareous corpuscles occurring in the parenchyma of Taenia saginata. A distinct Feulgen-positive reaction is seen in most of these corpuscles. The material yielding this positive reaction is apparently derived from the nucleus of certain mesenchymal cells from which these corpuscles supposedly originate. In some corpuscles, which are probably at the early stage of formation, the nucleus of such a mesenchymal cell is clearly seen adhering to the surface of the corpuscle. The identity of the nucleus of such cells is apparently lost in the fully formed corpuscle. Each corpuscle has a concentric appearance and is probably formed in successive layers.

Two new species of Giardia are described: G. wenyoni sp.nov., from the duodenum of slender loris, Loris tardigradus lydekkerianus, and G. dasi sp.nov. from the duodenum of palm-civet, Paradoxurus hermaphroditus hermaphroditus.

The distinguishing features of G. wenyoni are (measurements in microns): range of length 12·0–20·0, average 15·6; range of breadth 5·5–11·5, average 8·8; ratio of length to breadth 1·7; distance from anterior end to centre of nucleus 4·5; centre of nucleus to ends of lateral shields 7·0; ends of lateral shields to posterior end 3·6; breadth across centre of nucleus 7·7; length of the sucker 6·2; the ratio of body length to the length of sucker 2·5. The nuclei do not lie parallel to the axostyles. Each nucleus contains chromatin granules along the periphery.

G. dasi is distinguished by its dimensions which are (in microns): range of length 11·8–20·0, average 15·5; range of breadth 5·0–12·5, average 7·2; ratio of length to breadth 2·1; distance from anterior end to centre of nucleus 4·7; centre of nucleus to ends of lateral shields 6·0; ends of lateral shields to posterior end 5·4; breadth across the centre of nucleus 6·6; length of the sucker 6·0; the ratio of body length to length of sucker 2·5. Chromatin granules are present in the form of a ring in the centre of the nucleus. The most characteristic feature of this organism is the presence of certain large granules in the cytoplasm.

Retortamonas cheloni sp.nov., from the large intestine of the starred tortoise, Testudo elegans Schoepff, 1792, is described. Body oval with a long caudal process; length of body 4·2–11·5μ, 7·9 average; breadth 3·0–6·5μ, average 4·4; length of caudal process 1·0–7·0μ, average 4·0. Nucleus round, situated at the extreme anterior end, with a thin ring of chromatin adjacent to the nuclear membrane and sometimes an endosome. Cytostome deep, extending one-third to one-half of the body-length and bordered by two siderophilic threads. Close to the nucleus are two blepharoplasts from which arise two unequal flagella and the two siderophilic threads. Periplast rigid.

During August 1953, the Hon. Miriam Rothschild, with the assistance of Dr Schifferli and Fritz Muhlethaler, succeeded in obtaining three nests of the Alpine chough Pyrrhocorax graculus L. on the Niesen (1200 m.) Bernese Oberland, Switzerland. Three nests of the snow finch Montifringilla nivalis L. were collected during the same period from behind gutters and under eaves on the railway buildings at Eigergletscher (2320 m.), Bernese Oberland, immediately after the young birds had flown.

Five new species of Myxosporidia are described and figured. They are: Ceratomyxa auerbachi, Davisia longibrachia, Myxidium laticurvum, Parvicapsula unicornis and Sphaerospora irregularis. The first two are parasitic in the gall-bladders, while the remaining three in the urinary bladders of various teleosts in the North Sea.