1. Measurements were made of the head length, head width, total body length, antenna length, length and breadth of 3rd antennal segment of head and body lice from natural infestations. In all measurements (except the last) the means were significantly different for. the two forms, but in all cases there was considerable overlap.

2. Head lice reared continuously on the body for forty-three generations (over 2 years) did not change systematically in size. Body lice reared under similar conditions were likewise constant.

3. There was a highly significant difference between mean measurements of all the samples of head lice reared for up to 2 years on the body when compared with body lice reared for a similar period in the same way. The means for lice worn 24 hr. per day were less than those worn 12 hr. per day in both strains. An experiment showed that this is probably due to a difference in average temperature.

4. The mean live weights of head and body strains were even more distinct than linear dimensions on the several occasions when these were recorded.

5. Measurements of the dimensions of the opercula of the eggs of the two races and the numbers of air cells in them were distributed in the same way as the body measurements: that is, distinct means but overlapping individuals.

6. Ventral abdominal muscles in wild head lice are typically confined to segment 5. (The forty specimens examined adhered to this rule.) In wild body lice, muscles are usually also present in segment 4 as well.

7. Hybrids (female body x male head louse) were fertile for several generations. In size, the F1 generation was intermediate, but the F2 and F3 generations became identical with the body louse strain.

8. Eggs of the body louse strain hatched at the same time as those of the head strain, but the body strain reached a significantly higher percentage hatch.

9. The times of moulting during development were studied in both races in relation to differing opportunities to feed (24, 12, 6 and 3 hr. per day). The two strains showed very similar reactions in regard to speed of development, but throughout there was a higher pre-imaginal mortality in the head strain.

10. Head lice were shown to be considerably more susceptible to starvation than body lice.

11. If adults of the two strains are mixed, there is no tendency towards homogeneous mating. Of the mixed matings, those between body louse males and head louse females are much more common than the reverse.

12. Female head lice show a slight difference in their egg-laying preferences when offered a choice of hair, voile and tape.

My thanks are due to Prof. P. A. Buxton, F.R.S., for a number of helpful suggestions based on his extensive knowledge of louse biology and to Dr J. O. Irwin for critical comments on the statistical issues.

1. The number of third stage larvae of Trichostrongylus retortaeformis on different portions of herbage was studied. Three plant-types were used: Festuca sp., Clover, and Carex sp.

2. On Festuca spp., 5·5 in. in height, 90% of the total number of larvae occurred on the lower 3 in. of the blades; 50% occurred on the basal 1·5 in. On the same species, 3 in. high, 90% were found on the lower inch. This showed that the distribution on the blades was not limited by the total distance the larvae were able to travel. Nor was it limited by the rate of movement, because the form of the distribution was not altered after 3 days.

3. Larvae were found to be evenly distributed vertically over the stems and leaves of clover.

4. On Carex vulgaris 10 in. high the larvae were limited to the lower 2 in.

5. The distribution of larvae in the soil, ‘mat’ and herbage was recorded monthly throughout the year. During the warmer months of June, July and August the majority of larvae were found on the grass blades, and more larvae occurred in the soil than in the ‘mat’. During September, October, April and May more larvae were found in the ‘mat’ and fewer were found on the blades and in the soil. From November to March nearly all the larvae occurred in the ‘mat’. From December to January no larvae were found on the grass blades or in the soil.

6. Climatic conditions in the herbage were studied.

7. It was shown that the temperature below the top of grass blades may differ considerably from the air temperature. Differences of 10° F. were recorded between the tips and bases of grass blades. In general, there was a gradient of temperature established between the upper and lower parts of the grass.

8. High humidities occurred in the lower parts of the grass, even when atmospheric humidity was low. The relative humidity at the tips was never higher than that at the base of the blades.

9. The rate of evaporation decreased towards the base of the blades.

10. The light intensity decreased towards the soil. Midway between the top of the grass and the soil the light intensity fell rapidly.

11. The height, density and type of herbage modified the effect of the climatic factors.

12. It was concluded that the vertical distribution of larvae could be explained without reference to geotropism and that most of the larvae occurred in that portion of the herbage in which there was least climatic change.

The writer wishes to thank Prof. A. D. Hobson for advice and criticism and Mr W. Lyle Stewart, M.R.C.V.S., for encouragement and the provision of facilities, and Dr G. Lapage for helpful criticism and advice in the preparation of the MS. Thanks are also due to King's College, University of Durham, for a grant from the College Post-Graduate Research Fund.

1. Eggs and larvae of Trichostrongylus retortaeformis were used.

2. The rate of hatching of eggs was shown to be mainly related to temperature. From November to March, when maximum temperatures were below 50° F., there was no hatching. When maximum temperatures of 50–55° F. occurred eggs hatched on or before the fifteenth day, but never during the first 8 days. Eggs hatched in 8 days or less when maximum temperatures of 60–80° F. occurred.

3. When the rate of evaporation in the air was high, eggs still hatched and reached the infective stage, the grass blades reducing the rate of loss of moisture from the faecal pellet. Laboratory experiments show that eggs may not develop to the infective stage if the faecal pellets are on a grassless portion of the pasture. This is most likely to occur when the rate of evaporation is high and the temperature low.

4. Hatching may be delayed by cold conditions, but some eggs remain viable for long periods and they hatch when the temperature rises. Eggs passed by the host in the autumn can survive a cold winter and hatch in the spring, but eggs passed during the coldest period die.

5. During periods when the maximum temperature never exceeded 55° F., little or no migration of larvae occurred. When temperatures rose above 55° F. the number of larvae migrating increased; but rise of temperature was associated with increase in the rate of evaporation. High rates of evaporation reduced the number of larvae migrating on the grass blades.

6. Some infective larvae died soon after exposure on grass plots, but a small number survived long periods. In cold weather some larvae were still alive after 20 weeks. A high death-rate occurred in warm weather. A large proportion of the larvae died during periods in which the rate of evaporation was high; in one of these periods 95% of the larvae were dead at the end of 4 weeks' exposure.

7. The number of larvae on grass blades of a pasture was shown to be dependent, at any time, upon the climate at that time, and upon past conditions which had influenced hatching and survival:

In March 1945 the writer had the opportunity of examining a young specimen of the South African lemur, Otolemur crassicaudatus garnetti, formerly known as Galago garnetti (Ogilby), sent into the Museum by Mr N. A. W. Macpherson from Cato Ridge near Pietermaritzburg, Natal. Fourteen Cheyletid mites were found in the fur on the back of the animal, some of them fairly active and none attached to the hairs of the body. In August 1946 a further number of mites belonging to the same family was taken from the fur of the slender mongoose, Myonax cauui punctulatus (Gray) captured at Mooi River. Finally, a number of larval Trombidiform mites were collected from the skin of a golden mole, Amblysomus hottentotus longiceps (Broom), donated by Mr R. S. Crass from Curry's Post near Pietermaritzburg.

1. The respiratory horn of Psychoda severini Tonn. subsp. parthenogenetica Tonn. is described. Within the tubular horn lies the felt chamber, which meets the horn wall at a number of thin circular regions, the pits, and communicates, through the annulated base of the horn, with the tracheal extension. This has a characteristic retiform thickening and is continuous, at the lower end, with the spiracular chamber, from which a trachea runs to the prothoracic spiracle of the imago.

2. At the upper end of the tracheal extension lies the closing mechanism consisting of a lever, and a muscle surrounded by a cuticular sheath. It is suggested that the mechanism functions by compressing the tracheal extension, and that the sheath serves to protect the muscle from the action of the moulting fluid.

3. The respiratory horns of fourteen of the British species of Psychoda are described, and it is shown that Ps. spreta Tonn., Ps. albipennis Zett. and Ps. trinodulosa Tonn. are like Ps. severini in possessing long lateral tubes in at least the basal half of the horn, whereas Ps. alternata Say, Ps. surcoufi Tonn., Ps. cinerea Banks, Ps. gemina Eaton, Ps. lobata Tonn., Ps. grisescens Tonn. and Ps. setigera Tonn. have only short lateral tubes. The two species Ps. phalaenoides L. subsp. elongata Tonn. and Ps. crassipenis Tonn. are alike in having a two-branched felt chamber, and Ps. brevicornis Tonn. has a flat triangular horn with a three-branched felt chamber and a cluster of air-containing tubes at each corner.

4. An account is given of the development of the respiratory horn of Ps. alternata Say. The horn arises as an outgrowth from the larval prothoracic imaginal disk, and the felt chamber forms by an invagination of its posterior wall. The tracheal extension arises as an invagination of the disk and subsequently acquires a connexion to the felt chamber.

5. The development is compared with that of Chaoborus plumicornis, and it is concluded that Weismann's theory of the origin of the horn from two distinct cell layers is not applicable to Psychoda.

6. The various terms that have been applied to the respiratory horn are discussed, and the conclusion is reached that though none of them is satisfactory, it is premature to devise a new scheme of nomenclature.

Grateful acknowledgements are due to Dr Ll. Lloyd for his help and advice in the course of this work. Some of the material was collected whilst the writer was in receipt of a grant from the Department of Scientific and Industrial Research, to whom acknowledgements are also due.

The egg of Ixodes ricinus L. is described, and the increase in size during development is noted. It is suggested that the increase is due to the absorption of water. The egg wall consists of exo- and endochorion with a thin vitelline membrane, which becomes thicker as development proceeds and assumes a laminated appearance. The secretion layer of Gené's organ is described, and appears to function as a cement for holding the eggs together in the cluster. Chemical tests show it to be of a waxy nature.

It is deduced from experimental evidence that the egg shell is not absolutely rigid, and the weight of evidence favours the view that the shape of the egg shell is maintained by the internal pressure of the egg contents, and the elasticity of the shell.

The development processes as seen in the living egg are described. Hatching from the egg shell is brought about by a muscular force acting on a limited area at the posterior pole of the egg.

The writer is indebted to Mr Robert David, of Longlands Farm, Pyle, Dr A. D. Lees, of the Agricultural Research Council, and Mr Simeon, of the Glamorgan War Agricultural Executive Committee, for supplies of material; to Mr T. W. Tyssul Jones, M.Sc., for his assistance in checking the measurements of the egg dimensions, and to Mr L. Cowley, M.Sc., Assistant Curator (Department of Zoology), National Museum of Wales, and Dr P. Tate, Molteno Institute of Parasitology, Cambridge, for reading the original script and for making many useful suggestions and modifications.

Observations have been made on the distribution of adult and pupal keds over the body of sheep and lambs, and the seasonal changes in density and distribution have been followed by a series of counts on the same sixteen sheep throughout a period of 13 months.

The method of assessing the adult population by counting the living keds was checked by killing and subsequently counting them, and is believed to give approximately correct results. Pupal estimations by the ‘live-count’ method gave results apparently 50 % below the actual values.

The ked population builds up rapidly during late winter and early spring to a maximum in April and early May. A decline begins in May, and by June the population has decreased very considerably. During summer the unshorn lambs show a continued decrease, which may be due in whole or part to loss by transference to the shorn sheep.

The greatest concentration during the peak infestation is on the chest, lower shoulder and lower rib wool. In winter and spring the population is more generally distributed, and may show a preference for the upper over the lower side wool. In summer the back is practically deserted and the upper sides only sparsely populated. The throat and chest region is a favoured site the year round, and there is some indication that the throat may be a breeding area.

Generally speaking, the adult and pupal populations are proportionately distributed. In late spring, however, puparia tend to be laid to a greater extent, relative to the adult population, in the lower than the upper surface fleece.

The significance of the seasonal population shifts is discussed, and a method of eradicating keds from a flock by summer dipping of the lambs is outlined.

An essentially synthetic medium has been developed for the cultivation of Entamoeba histolytica in association with organism t. It consists of buffered saline solution containing trace minerals, twelve amino acids, ten synthetic vitamins of the B complex, nucleic acid, cholesterol and rice starch. Cultures have been carried continuously in this medium for a period of eleven months.

We are greatly indebted for materials used in this study to the following: Drs M. S. Dunn, J. J. Eiler, D. M. Greenberg, L. D. Greenberg, E. E. Howe, H. D. Lightbody, H. S. Loring, H. Molitor, E. D. Stewart and E. L. R. Stokstad.

The authors wish to acknowledge the valuable advice and material aid provided by Drs Gladys Emerson and Gilberto G. Villela during the initial phase of this study.

A new species of the giant phyllobothriid genus Dinobothrium (D. keilini n.sp.) is described from the blue shark (Carcharinus glaucus); it is compared with D. planum Linton, found for the first time from British waters, in the basking shark (Cetorhinus maximus), and the structure of both is discussed in relation to that of the genotype, D. septaria van Beneden. A fourth species, D. paciferum n.sp., also from the basking shark, is described, and though only a tenth the size of the other species, it shares most of their diagnostic scolex characters. It has eight true suckers above the four pendent bothria: in D. planum there are four true suckers and four pseudo-suckers, while in D. keilini there are only four true suckers, and D. septaria is said to have four pseudo-suckers alone. The nomenclature of the older species is revised, and the genus redefined.

Attention is directed to the adaptations in these large cestodes which facilitate interchange with the substratum: the development of lateral furrows through which the main excretory canals open to the exterior. There is also a ventral furrow, which in the nascent segments is an open cleft: this accommodates the growing uterus and permits a protracted gravid phase of the proglottides in situ. The effect is of five longitudinal hinges, which allow of considerable lateral expansion of the thick-walled strobilus. The smaller D. paciferum lacks these modifications, and the cylindrical segments are apparently detached in the gravid state. An explanation is offered for the conflicting accounts of the lateral extent of the vitellaria in this genus: there is a lateral contraction of the ventral vitelline reticulum as the ovarian phase waxes. In D. paciferum the vitellaria completely encircle the proglottis at the inception of the ovarian phase.

Notes are given on the selachiàn hosts examined, their food and the other parasites present. The relationships of Dinobothrium to other phyllobothriid genera and to Tetrabothrius are discussed.

In one electric ray, Torpedo nobiliana, a single immature strobilus of another kind of phyllobothriid was found; it is probably a new species of Monorygma, though it has slight resemblances to Calyptrobothrium—a genus characteristic of electric rays. The boat-shaped bothria are held at an angle from the scolex by contractile buttress-like wings, and at their proximal end there is a relatively large and complex sucker. Affinities with related genera are discussed and the nomenclature of Monorygma angusta (Linton) is emended.

Trypanosoma cruzi is easily cultivated in tissue cultures of chick embryos, but it was not possible to infect chicks with trypanosomes cultivated for more than 2 years in chicken cells.

The trypanosome cycle takes place in one cell unit.

The number of trypanosomes formed in one cycle depends on the volume of the host cell.

The transformation of the leishmania form into the flagellate form begins when the cell is full of parasites, and occurs in 12–24 hr.

The intracellular trypanosome, immediately after the crithidia form, is broad and short, the thin form probably being a later phase of the evolution of the parasite.

Division of the adult trypanosome, or mating between the thin and broad forms, was never seen.

At the beginning of the infection the cells with-stand the parasites and continue to proliferate, but finally they are destroyed.

The determination of Hyalomma sp. is discussed. In the material examined from Palestine the genital aperture of the female, the cuticle in the proximity of the stigmata and the number of ‘tunnels’ in the anterior border of the scutum are characters which facilitate diagnosis.

1. Pure-line breeding of Calliphora erythrocephala is difficult owing to the fact that gravïd females will oviposit at a distance from decomposing meat and the newly hatched larvae will crawl long distances and pass through minute openings to reach the food.

2. A simple and convenient cage for breeding blow-flies is described.

3. To obtain eggs free from contamination meat is plunged in boiling water before being put in the cages; and the vessel in which it is placed is sup ported on a glass cylinder standing in a dish of water.

4. The larvae are fed on horse-meat placed upon sawdust in a large watch-glass resting upon sawdust in a bowl. The bowl rests upon a support surrounded by water.

5. Pupation occurs in the sawdust beneath the watch-glass and puparia are separated from the sawdust by sieving.

6. Pupae are kept in glass dishes with closely fitting covers to prevent parasitism by Hymenoptera.

7. At a temperature of 21° C. the complete life cycle takes about 1 month.

1. Qo2 values for Haemonchus contortus egs varied between − 9·7 and − 12·6 according to the degree of development of the embryos. The r.q. was in the region of 0·6.

2. Young infective larvae of Nippostrongylus muris had a high Qo2 (−18·4), which fell as the larvae aged. Third stage Haemonchus contortus larvae gave similar results. The respiration was not affected by exsheathment.

3. Adult parasites gave Qo2 values as follows: Ascaridia galli, − 2·5; Nematodirus spp., − 5·1; Nippostrongylus muris, − 6·8; Neoaplectana glaseri, − 12·6. When calculated on a surface area basis, Ascaridia galli had an oxygen uptake which was much higher than that of the other organisms.

4. Qco2 values were small. The r.q. of infective larvae, which contain fat as reserve material, was about 0·72. The other forms which contained much glycogen as well as fat had r.q. values between 0·6 and 0·7. A. galli was an exception in that an r.q. of about 0·95 was obtained.

5. Potassium cyanide inhibited respiration in all the forms examined.

The author is indebted to Dr R. W. Glaser for supplying a strain of Neoaplectana glaseri.

Four new species of myxosporidian parasites are described from marine fishes from Plymouth: Sinuolinea rebae n.sp., from the urinary bladder of Solea solea; Leptotheca vikrami n.sp., from the gall bladder of Zeus faber; Zschokkella russelli n.sp., from the gall bladder of Gaidropsarus tricirratus and Ciliata mustela; and Zschokkella sturionis n.sp., from the gall bladder of Acipenser sturio.

The various terms used in describing the spore of Myxosporidia are reviewed and revised.

A new classification is proposed of the order Myxosporidia.

I wish to thank the Director of the Marine Biological Association's Laboratory for all the facilities he has enabled me to enjoy during my stay at Plymouth, by dedicating a new species of Zschokkella to him. As a mark of gratitude, and with a deep sense of respect to His Highness the Maharaja of Narsinghgarh State, C.I., I take the liberty of dedicating to him the new species of Leptotheca I have discovered. But for his encouragement and help in the early stages of my career it would have been impossible for me to apply for the India State Scholarship which I now hold. I take this opportunity of expressing my thanks to Miss N. G. Sproston for her unfailing help and encouragement during the present studies and am very grateful to her for going through the manuscript critically.

We need a fuller understanding of the feeding habits of fleas on rodents, both to help in the study of the epidemiology of plague and also in carrying out laboratory experiments on the same subject. In an earlier paper (Buxton, 1938) I described a ‘synthetic mouse hole’ in which I kept a rodent with a population of fleas (Xenopsylla cheopis) under controlled conditions of climate and feeding for periods of many days; with this I obtained some measure of the progeny which resulted under a variety of conditions. There was evidence that the mouse ate a number of the fleas, and I never controlled this variable, which was erratic and sometimes very large. We attempted to avoid the destruction of the fleas by feeding them on a baby mouse, which was changed at intervals, so that there was always one in the experimental vessel. In a postscript to the above paper it was shown that the baby mouse does not consume the fleas, almost all of which are alive when the experiment has lasted a week; in that period the adult mouse may eat about half or more of the fleas. Further experiments are in progress on the factors which determine the destruction of fleas by the mouse, and on the proportion of fleas which are actually found on the mouse under different conditions of temperature and so forth. In the present note, I shall confine myself to studying the baby mouse, as a host of X. cheopis. All the experiments here described were carried out between 1937 and 1939, though it has not till now proved possible to tabulate and consider the results. The execution of the work was in the hands of Mr S. Smith, whose help is acknowledged.

1. Attempts, made over a period of more than 6 months, to produce a strain of Plasmodium gallinaceum resistant to mepacrine failed.

2. A strain of P. gallinaceum resistant to daily doses of 0·08 mg./20 g. of pamaquin was obtained after approximately 8 months' treatment with the drug.

3. A strain of P. gallinaceum resistant to the maximum dose of paludrine which the chicks would tolerate (1·0 mg./20 g. twice daily) was obtained after 4½ months' treatment with gradually increasing doses of the drug.

4. The exo-erythrocytic parasites of P. gallinaceum formed in chicks infected with a paludrine-resistant strain are themselves resistant to the drug. It is not, however, considered probable that the development of resistance is due to the action of the drugs upon the exo-erythrocytic parasites, as the technique used was one which reduced their number to a minimum.

5. A strain of P. gallinaceum resistant to paludrine showed a normal sensitivity to mepacrine and pamaquin, but was resistant to 4430, the methyl homologue of paludrine.

6. Chicks carrying a latent infection of the normal strain of P. gallinaceum were immune to infection with the paludrine-resistant strain; and conversely chicks carrying a latent infection of the paludrine-resistant strain were immune to infection with the normal parasite.

7. A paludrine-resistant strain of P. gallinaceum retained its resistance to this drug after five cyclical passages through mosquitoes without intervening drug treatment.

The taxonomy of larval and nymphal stages of H. savignyi, H. detritum, H. marginatum, H. dromedarii and the nymph of H. aegyptium are described.

The material for the first four species was obtained from laboratory-bred specimens. The bionomics of these species was studied in the laboratory. Their behaviour under natural conditions still remains to be studied.

A considerable loss of water in the flea larva, through its defaecation and excretion as the result of the absence of rectal glands, through a profuse evaporation from the surface cuticle on account of its being a soil inhabitant, and from its tracheal system owing to the absence of an efficient closing apparatus of the spiracles, is compensated by the absorption of water with the food and through the cuticle, and by the utilization of metabolic water.

It has been proved, by conducting experiments on the food composed of dried horse blood and yeast, with different degrees of moisture contents, and by controlling the quantity of the desiccated food and the duration of its exposure to a low effective humidity of 60% at 22° C., that the chief source of the gain of water in the larva of Xenopsylla cheopis is through the food.

The closing mechanism of the spiracles of the flea larva plays only a small part in the control of evaporation at medial temperatures but not at extreme ones.

There are intrinsic differences in the water requirements of the flea larvae of the two sexes, being slightly less in the male larva than in the female larva.

I am greatly obliged to Lt.-Col. Sir Sahib Singh Sokhey, Director, Haffkine Institute, Bombay, for affording me facilities for the pursuit of these investigations. Mr T. N. Raste has helped me in the calculation of the data statistically, for which I am grateful to him.