The attempts of Chorine (1938), Gavrilov (1938), Gavrilov, Bobkoff & Laurencin (1938) and Rita (1940) to infect chick embryos with Plasmodium gallinaceum, using either a suspension of sporozoites or infected blood, yielded negative results. They tried inoculation by deposition of the infecting material on the chorion-allantois or by injection into a blood vessel of this membrane, and the negative results observed led Rita to make various deductions by comparing them with other infections which appear in the embryo and not in the adult animal.

The unfed tick gains water from humid air or from water in contact with the cuticle, and loses water by evaporation. Whilst attached to the host the tick is gaining water from the ingested blood and losing water in the excrement. The engorged tick usually lacks the ability to take up water from humid air.

The exchange of water takes place mainly through the cuticle. Regulation of the water balance is therefore brought about by the activity of the epidermal cells.

The cuticle comprises two principal layers, the epicuticle and endocuticle. The epicuticle is overlaid by a lipoid possessing important waterproofing properties. The pore canals, which traverse the endocuticle, are occupied by cytoplasm, and may in consequence play an important role in the active -transfer of water through the cuticle: they do not penetrate the epicuticle.

Water loss from the unfed tick is not closely related to saturation deficiency, particularly at high humidities. This departure is due to a physiological cause, namely, to the ability to secrete water. The effects of this activity are such that a state of equilibrium is attained at a relative humidity of about 92%: at lower relative humidities the tick loses water by evaporation, while at higher humidities it takes up water. The retention of water at humidities below the point of equilibrium is due not only to the physical properties of the epicuticle but also to this secretory activity, for water loss increases when the tick is temporarily asphyxiated, poisoned with cyanide or injured through excessive desiccation. Near the point of equilibrium the loss or gain of water over a wide range of temperature is determined by the relative humidity.

The uptake of water from humid air occurs when the tick is in a desiccated condition but ceases as the normal water content is restored. After previous exposure to saturated air the adapted tick at first loses water at relative humidities above the point of equilibrium, but later comes to retain water completely.

Both unfed and engorged ticks possess the ability to prevent or to limit temporarily the entry of water in contact with the cuticle.

The engorging female, originally weighing about 2 mg., ingests about 600 mg. of blood. About 300 mg. or two-thirds of the contained water are usually eliminated before the end of engorgement. Evaporation from the cuticle may account for a considerable fraction of this, for the temperature to which the attached tick is exposed (about 37°C.) is, in Ixodes ricinus, above that temperature at which a marked increase in the permeability of the epicuticular lipoid takes place.

The nine species of ticks examined differ considerably in their powers of limiting evaporation. This may reflect specific differences in the nature of the epicuticular lipoid. The order of their resistance is as follows: Ornithodorus moubata; Dermacentor andersoni; D. reticulatus; Rhipicephalus sanguineus; Amblyomma cajennense and A. maculatum; Ixodes canisuga; I. hexagonus; I. ricinus. In dry air water loss throuǵh the cuticle is 10–15 times more rapid in Ixodes ricinus than in Dermacentor andersoni. The more resistant species also take up water through the cuticle after desiccation; indeed, the rate of uptake over a unit area of cuticle is approximately the same in all species of Ixodidae. Uptake thus appears to be limited by the ability of the epidermal cells to secrete water.

Stocks of Dermacentor andersoni, Rhipicephalus and Amblyomma spp. were kindly supplied by Dr R. A. Cooley, Director of Entomology, Rocky Mountain Laboratory, U.S.A., through the good offices of Prof. P. A. Buxton, F.R.S. I am also indebted to Dr H. H. Green of the Veterinary Laboratory, Weybridge, for providing useful facilities, and to Dr V. B. Wigglesworth, F.R.S., for his generous help throughout the various stages of this work.

An account is given of a composite virus disease of tobacco for which the name tobacco rosette has been suggested.

The two component viruses, named the mottle and vein-distorting viruses respectively, have been separated, and their symptomatology and methods of transmission described. The mottle virus is both sap and aphis-transmitted, but the vein-distorting virus is aphis-borne only.

The symptoms and histopathology of the complex disease in the tobacco plant are dealt with in some detail. There are three main types of symptoms: (1) intense rosetting, (2) splitting of the tissues, (3) formation of enations on the under-surface of the leaves.

The splitting of the tissues has been examined microscopically, and a number of photomicrographs are given illustrating the formation of the fissures. It is suggested that there is a concentration of virus in the cambium which prevents the formation of the normal xylem. Abnormal tissue and giant cells are formed in the cortex and pith. This appears to set up stresses which cause the splitting.

The insect vector of the complex disease is the aphis Myzus persicae Sulz. Another aphis, M. pseudosolani Theob., is also a vector but is less efficient than M. persicae.

The writer's thanks are due to Prof. F. T. Brooks, F.R.S., with whom he discussed the histopathology of the rosette disease, to Dr Roy Markham for taking the photographs illustrating Pl. I, figs. 2–5, and to Mr Charles Harpley of the Molteno Institute for his assistance in taking' the photomicrographs.

For some years past in Northern Province, Nyasaland, work has been in progress to determine the mortality amongst native cattle due to east coast fever (Wilson, 1944). As an integral part of such a survey, routine tick collections were made during cattle inspections. It was then intended to map the various species of tick concerned in the hope that their geographical distribution might offer a partial explanation for the prevalence or absence of east coast fever in certain areas. Such a map for the western portion of Kenya Colony has been provided by Lewis (1939), ‘according to the groups of dominant species of ticks’; but in Kenya, climate, soils and vegetation show wide contrasting variations, and conditions are scarcely comparable to those existing in the smaller territory of Nyasaland.

A new virus disease of tomatoes is described for which the name tomato black-ring is suggested. The host range of the virus is wide but no insect vector has yet been identified. The longevity in vitro of the virus is 7 days or longer, the thermal inactivation point is about 58° C. and the concentration of the virus in the host plant is low. Tomato black-ring is essentially a disease of young plants which rapidly lose their symptoms if they survive the severe initial infection. The virus is carried without symptoms by a large number of miscellaneous plants.

Note added in proof. In a private communication Kassanis has pointed out that the tomato black ring virus produces enations on the undersides of the leaves of cucumber. The writer has confirmed this but finds that the enations develop only in the greenhouse type of cucumber, never on the outdoor or ridge variety. The enations do not seem to develop under winter conditions.

The writer's best thanks are due to Miss Margaret Short for her assistance in this work and to Dr Roy Markham for taking the photographs.

1. Experiments are described on the transmission of mottle and vein-distorting viruses by aphides.

2. A quantitative analysis is made of Watson's experiments on the aphis transmission of persistent and non-persistent viruses. The principal features of the experimental results can be explained in terms of different rates of inactivation of the virus in the insect.

3. It is shown that these considerations explain why non-persistent viruses are more commonly sap-transmissible than persistent viruses.

An account is given of experiments on the aphistransmission of the composite virus disease of tobacco known as rosette. It is shown that the component viruses—the vein-distorting and mottle viruses—persist for long periods in the body of the aphis, and that as many as twenty consecutive tobacco plants can be infected in 24 hr. serial transfers without the insect having recourse to a fresh source of virus.

The aphis Myzus persicae is the most efficient vector, the aphis M. convolvuli being less effective. The aphides M. circumflexus and Macrosiphum gei failed to transmit the virus.

It is shown that the mottle virus can only be transmitted by the aphis when it is accompanied in the plant by the other component of the rosette disease, the vein-distorting virus. The latter virus is easily transmitted by the aphis, either alone or in combination with the mottle virus.

The writer's best thanks are due to Miss Margaret Short for her assistance with the large numbers of aphis-transmissions, and to Dr Douglas Lea and Dr Roy Markham for suggestions in the course of the work.

The nematodes recorded in the present paper were obtained from fishes caught on some of the deep-sea fishing grounds to the west of Ireland, namely, the Porcupine Bank and Irish Atlantic Slope, and from the Irish Sea. The writer is indebted to Mr S. J. Hughes and Mr J. Llewellyn for the collection of material from the deep-sea fishing grounds, excursions having been made for the purpose in a commercial trawler in August 1938 and July 1939. The majority of the nematodes were collected by Mr S. J. Hughes during the 1939 excursion, the first excursion being devoted mainly to the collection of trematodes and cestodes. A record of the trematode and cestode parasites obtained during both years has already been published (Rees & Llewellyn, 1941). Nematodes from fishes in the Irish Sea have been obtained at intervals from 1936 onwards.

The material which forms the basis of this note consists of two species of Anoplura, namely, Neohaematopinus echinatus (Neumann) and Hoplopleura maniculata (Neumann), both from the common North Indian five-striped squirrel, Funambulus pennanti pennanti Wroughton, collected at Benares (United Provinces). Since Neumann's (1910) description of the two species from ‘Sciurus palmarum Gm.’ (vide infra) from Rajkote (Kathiawar) and Scotophilus wroughtoni(?) from Navapur (W. Khandesh Dist.), there appears to be no other Indian record.

Life histories of the Trombidiidae, or, for that matter, other families of mites have, with few exceptions, not been studied and very little information is available as a guide. This is not entirely the fault of the acarologists, as not one of them was employed in any country of the world entirely upon the study of mites. Most of them, if official, were entomologists who could spend only a fraction of their time on mites. Their time was spent therefore on systematics, an essential branch of acarology.

During five months spent in Colombo (April–August 1944) a large number of small mammals and birds were examined for larval Trombiculinae.

From November 1944 to February 1945 similar investigations were carried out on the Maldive Islands. The number of species obtained included three species of the genus Gahrliepia Oudemans, 1912 (not included in this paper), Trombicula deliensis Walch, 1923, Trombicula acuscutellaris Walch, 1923, Neoschöngastia indica Hirst, 1915, Walchia turmalis Gater, 1932 (a second species of Walchia not included in this paper), a new species of Schöngastia herein named ‘maldiviensis’ n.sp., and Womersleyia minuta n.g., n.sp.

An account is given of the coprophilic habits of the holotrichous ciliate, Balantiophorus minutus Schew., and of the effect upon it of urine.

Experiments are described in which attempts were made to grow the ciliate in a wide range of human faeces of varying consistency and from both normal and diseased subjects. Abundant growth was obtained in normal faeces, both before and after dilution; but no growth took place in the undiluted faeces of softer or liquid consistency from various cases of intestinal disorder, even dilution frequently failing to render these a suitable medium. Moreover, the ciliate could not be recovered from such abnormal faeces by subculturing.

This behaviour was due to two primary factors:

(1) the high osmotic pressure obtaining in liquid stools which causes plasmolysis of the ciliates, and (2) the presence in the stools of unaltered bile salts, owing to the rapid passage of material through the intestinal tract. It was demonstrated that bile salts, even in very low concentrations, are highly toxic to B. minutus. Two secondary factors probably also serve to limit growth, namely, the presence of drugs with a toxic or depressing effect on the ciliate, and the presence of urine, which is not only highly lethal but also mixes more readily with a liquid than with a normal stool.

It was shown that the lethal action of urine upon the ciliate was due primarily to osmotic pressure, and, to a lesser degree, to the toxic effect of ammonia sometimes present in the urine. It was demonstrated that a concentration of urine as low as 5% inhibited multiplication in ordinary cultures, while as little as 1% prevented growth when admixed with normal faeces. It was further shown that urea has a depressing effect upon the reproduction of B. minutus. Paramecium caudatum was shown to be also susceptible to the lethal effect of urine.

Investigation of the effect of hypertonic solutions has shown that the limiting osmotic pressure which B. minutus can withstand for a prolonged period is represented by a solution of non-electrolyte with a depression of the freezing-point of about 0·60° C., or by a solution of an electrolyte with a depression of the freezing-point of 1·2° C. (represented by 1·9% sodium chloride solution) which is equivalent to about 6000 mm. Hg (8 atmospheres). It was also shown that osmotic pressure is not the principal limiting factor to the growth of the ciliates in such stools. The ability of other ciliates to live in hypertonic solutions is discussed and the conclusion is reached that B. minutus is more resistant than is usual among freshwater forms.

Experiments carried out on mice established that the cysts were incapable of passing through the mammalian alimentary tract and developing in the faeces after passage, so proving that B. minutus is an exogenous coprozoon.

It is concluded that (i) only polysaprobic Protozoa capable of movements in a viscous medium can lead an existence in undiluted faeces; (ii) under natural conditions urine probably acts as a limiting factor to the development of coprozoic ciliates in faeces; (iii) coprozoic Protozoa are derived from the soil fauna and have in turn largely contributed to the sewage fauna.

During the course of investigations into the distribution and seasonal activity of the tick, Ixodes ricinus L., in South Wales (Edwards & Arthur, 1945), a male tick was recovered which on examination was found to be a member of Ixodoidea, but which differed from the normal male of I. ricinus L. It was recovered from Margam Moors (Glamorgan, South Wales) by one of the writers (D.R.A.) in 1945, whilst dragging a blanket over rough vegetation, a method previously employed by MacLeod (1932) for the recovery of ticks from grassland. This is the only specimen of its kind which has been found, despite the examination of several thousands of males during the past three years. It has therefore been considered desirable to place on record a description of the form. When placed in a tube containing ten unfed females of I. ricinus, no mating occurred. Under similar conditions a typical male of this species mated with one unfed female within 7 minutes of its introduction.

Montgomery (1917) showed that Nairobi sheep disease, a tick-borne gastro-enteritis of sheep and goats in East Africa, was caused by a filtrable virus transmitted most commonly by the brown tick, Rhipicephalus appendiculatus. The transmission of the disease by this tick was confirmed by Daubney & Hudson (1931, 1934), who demonstrated also that ticks infected in any instar usually transmitted the disease when fed in the succeeding stage on susceptible sheep; and that the virus ingested by a female fed on an infected sheep passed through the eggs to the larvae of the next generation.

The incidence of east coast fever in areas where the disease is endemic is associated with the common occurrence of the usual tick vector, Rhipicephalus appendiculatus. Outbreaks of the disease in other areas are sporadic or seasonal, and although, in many such instances, R. appendiculatus has been found either in isolated localities, or very sparsely distributed over the whole of an infected area, in other cases it has not been possible to collect even a single specimen of this tick. Collections of ticks from infected farms in these sporadic areas comprise such species as Boophilus spp., Rhipicephalus capensis, R. simus and R. evertsi or Hyalomma spp., Amblyomma spp., Rhipicephalus pulchellus and R. neavei.

1. The structure of the capitulum of I. ricinus L. is described briefly.

2. A stylet-like process is described in detail. Anteriorly it forms a distal attenuation, which widens out at its base near the point of attachment to the hypostome and is continued posteriorly as a distensible pouch overlying the pharynx. Anteriorly the stylet-like process is supported by a ventral sclerotized rod.

3. The stylet-like process effects closure of the pharyngeal orifice during contraction of the pharynx and so prevents the reflux of blood into the wound. In this it is assisted by the closure of the hypostomal gutter.

4. The stylet-like process appears to be a similar structure to that observed by Sen (1935) in three other species of Ixodid ticks and to be comparable in function to the tongue-like process described by Bertram (1939) in Ornithodorus spp.

The writer wishes to acknowledge his indebtedness to the Advisory Entomologist, Dr E. E. Edwards, in whose department the work was done; to Dr Alec Milne, Unit of Insect Physiology, Agricultural Research Council; Dr P. Tate, Molteno Institute of Parasitology, Cambridge, for reading the original script, for making many useful suggestions and modifications.

Several specimens of Phyllobothrium dohrnii (Oerley) were obtained from the intestine of Hexanchus griseus caught in the deep-sea fishing grounds on the Porcupine Bank to the west of Ireland. The species was first described by Oerley in 1885. Since then, several cestodes which are probably synonymous with this species, have been described by various writers. They are Crossobothrium laciniatum Linton (1889) from Odontaspis littoralis (the sand shark) at Wood's Hole, Mass., Crossobothrium campanulatum Klaptocz (1906) from Hexanchus griseus in the Gulf of Trieste, and Orygmatobothrium velamentum Yoshida (1917) from Cynias manazo (the bleeker) of Hiroshima, Japan.

1. A new monocystid gregarine is reported from the seminal vesicles of brandling worms, Eisenia foetida Sav. The morphology and movements of the trophozoite are described, and the stages of gametogony and sporogony are outlined.

2. The chromosome cycle is investigated. The haploid number of chromosomes is four, and the reduction division is shown to be zygotic.

3. The systematic position of the gregarine is discussed, and it is placed in the genus Apolocystis as A. elongata n.sp.

Chloride regulation. Following the ingestion of a blood meal the tick excretes about half the ingested water in the coxal fluid. The mean haemolymph chloride concentration before feeding is 1.00% and after feeding 0.96% NaCl; and that of the coxal fluid, 0.80% NaCl. These results confirm the values given by Boné (1943).

Morphology of the coxal glands. These comprise the coxal glands proper, which elaborate the bulk of the coxal fluid, and the smaller accessory glands of unknown function. Each flask-shaped coxal gland consists of two distinct regions, an outer ‘filtration chamber’ and an inner system of tubules. The latter lead to the external opening. The filtration chamber, which communicates with the tubules at only one point, is highly folded into an elaborate series of pockets and fingers which closely invest the tubules; numerous small muscle fibres inserted in these pockets pass outwards from the gland to attachments on the body wall. The histology of the two regions is entirely different: the filtration membrane is only 1–2μ in thickness and its cellular origin is much obscured: the tubule walls are 5–30 μ in thickness, are composed of cells with a dense, deeply staining cytoplasm, and are richly supplied with tracheae. In Ornithodorus delanoei acinus the walls of the sac-like coxal glands are lined both by ‘filtration membrane’ and by large irregular groups of ‘secretory’ cells; there are no true tubules.

Function of the coxal glands. The production of coxal fluid is under muscular control. It is believed that the contraction of the coxal gland muscles enlarges the filtration chamber and sets up a sufficient pressure difference across the membrane to initiate filtration into the gland. In the subsequent passage of the fluid down the tubules threshold substances such as chloride are reabsorbed. That the coxal fluid is primarily an ultrafiltrate of the haemolymph is suggested by (a) the rapid passage of dyes and even haemoglobin into the coxal fluid after injection into the haemolymph and (b) the very high rate of liberation of fluid. Serum albumen sometimes passes into the coxal fluid after injection but casein (and the normal haemolymph proteins) are fully retained.

Further details of tick distribution (Ixodes ricinus L.) on the pastures of a typical hill farm are given.

Sheep paths (tracks) and their borders have tick populations similar in density to that of the general pasture.

Sheep lairs (night resting places) have significantly lower nymphal densities than the general pasture. With males and females, though the difference is in the same direction, it is less well marked.

On the typical hill, the vegetation layer generally becomes thinner, and nymphal density decreases, with altitude. The case is not so clear with males and females. Provided vegetation conditions are suitable (i.e. sufficiently thick), altitude has no limiting effect on nymphal density distribution within the levels studied. Tick density distribution is therefore a function of vegetation conditions, the latter usually being affected by altitude.

Distribution of ticks on apparently uniform areas of vegetation is studied. Sampling methods are discussed. Probably no more than twelve nymphs per square yard of ground are present on the average in heavily infested pasture. The numbers of nymphs per 100 sq. yd. differed significantly. The number per acre (approx.) also differed significantly in rather more than half the cases observed. Larger areaunits within uniform stretches of pasture probably carry similar numbers of ticks.

Practical applications of the findings to the study of tick control are indicated.

Thanks are due to Dr V. B. Wigglesworth, F.R.S., Director, Agricultural Research Council Unit of Insect Physiology; Dr A. E. Cameron, Edinburgh University; and Captain the Hon. Claud Lambton, on whose farm the work was carried out.