(1) The medical importance of trombiculid mites is indicated and reference is made to their geographical distribution.

2. Methods used by investigators for assessing the distribution of the mites in the Far East are discussed as well as methods used in the study of Trombicula autumnalis.

3. A detailed account is given of a light-trap and the method of using it; the reaction of the mites to the trap is discussed.

4. The results of a detailed survey are presented to show the significance of the method in relation to the distribution and bionomics of trombiculid mites.

The main results of this survey are as follows:

(a) The mites are characteristically distributed in pockets of infection.

(b) A study of the ecoclimatic conditions favourable to mites shows that humidity is a limiting factor.

(c) The free-living larval stage disappeared from the soil in October, and nymphs were found in the soil in September. These facts, together with the results of laboratory breeding experiments at room temperatures, which showed that it was normal for nymphs to appear in October, indicate that the nymphal and adult stages over-winter.

(d) Mites are not associated with fruit bushes if the physical conditions of the soil are unfavourable. A tentative explanation is given to account for the frequent association of fruit bushes with miteirritation.

(e) The gregarious habit of clustering is primarily due to a tactile response.

5. It is concluded that the light-trap method offers a new approach to the problem of surveying an area in order to diagnose trombiculid mite infection. It is also of value in obtaining abundant material for laboratory investigations.

Doubt exists as to why, in endemic areas, a varying proportion of calves die of East Coast fever while others survive. A series of experiments was therefore conducted to ascertain if the number of infected Rhipicephalus appendiculatus engorging simultaneously on susceptible calves influenced the course of East Coast fever reactions. The ages of the calves used in the various experiments varied, but other conditions were kept as uniform as possible.

When ten calves were grazed in a 1-acre paddock where the number of infected R. appendiculatus was high, eight died of acute East Coast fever.

In the second experiment, seventeen calves in all were grazed in the same paddock. These calves were given some protection from infected R. appendiculatus infestation, as two of the calves were immune to East Coast fever and the ears of ten of the susceptible calves were sprayed with tickicidal solutions. Four died from acute East Coast fever and one of subacute East Coast fever complicated with a helminth infection.

Since it is concerned with filling in certain details of a picture, long since sketched in outline, the new work in this paper permits only a somewhat disjointed summary.

From a study of Ixodes ricinus L. in nature, the main new facts emerging are:

(I) Unfed adults in a deep vegetation layer such as presented by rough hill or moorland pasture dominated by bents, heather or bracken. (i) Practically all inactive unfed ticks are in the underlying mat, and nearly all of these in the upper portion of the mat. This distribution does not change, summer or winter. (ii) When the tick is active its progression is practically confined to the vertical, i.e. between its niche in the mat and the vegetation tips immediately above. Random undirected movements due to certain circumstances may achieve a 0–8 in. (average 2 in.) change of position in the horizontal plane; but there is apparently no ruling urge to move in the horizontal plane. (iii) The unfed tick comes to the vegetation tips to await a host for only a limited time during the 3-month activity season. Commonly this amounts to about five periods of 4–5 days each if no host is forthcoming. Between the periods of activity it returns to the upper mat. If it stayed constantly at the tips its survival time would be much shorter than normal. (iv) From nymphs engorged in spring, adults emerge in autumn but remain inactive for a considerable period. About half of them may perish within the first 100 days after emergence. Survivors become active during the following March–June. Effective life ends when the tick, if still unfed, finally stops coming to the vegetation tips, the only position from which a host can normally be achieved. After emergence, the effective life of the unfed adult deprived of a host is less than one year; and the actual life is not much more than one year at best. Thus adults not finding a host in spring will be ineffective, i.e. die without reproducing before the next activity season.

Confusion exists as to whether the immunity produced by one attack of East Coast fever is absolute or whether it requires to be maintained by reinfection.

During the present experiments mild transient infections have been produced in six calves, and in five cases the immunity has been incomplete and second attacks have followed reinfestation by infected ticks.

The time interval between the attacks has varied from 1 to 16 months, and it is suggested that when the interval is prolonged the second attack will be severe and may be fatal.

It is concluded that the durability of the immunity depends on the severity of the original attack, being durable when the attack is severe, and only transient and probably never solid when the attack is mild.

The temperature reaction is at the moment the best indicator as to the severity of the attack and the type of immunity evolved.

Spatial distribution is understood to connote distribution of density (including zero density) over the land surface at a given time. Combining fact and conjecture, the following is a theory of spatial distribution of Ixodes ricinus in Britain. The tick passes practically the whole of its 3-year life span on the ground, spending a total of only 3 weeks on hosts. A considerable amount of vegetational cover is necessary for efficient survival on the ground; the more important limiting circumstances in lesser cover seem to be humidity (conditioned by temperature) in summer, perhaps temperature (alone) in winter, and the activity of predators. A host is necessary for mating as well as food purposes. Though small at best, the tick's chances of achieving a host are greater the more hosts on the ground. In practice this means the more sheep, since the latter are by far the main hosts. For the most part, spatial distribution to-day can be explained adequately in terms of interplay between amount of ground-cover and of host-potential, with cover the master factor. Thus poor cover keeps the heavily stocked lowland pastures free of permanent tick population even when opportunity of colonization is offered. The tick is confined to the hills and moorlands with their deep vegetation layers. There, within limits, it is more numerous on a pasture the more universal the distribution of adequate cover (because it drops at random from the host) and the higher the host-potential. Among hill and moorland pastures, however, there are some cases where, despite ample cover and hostpotential, either (1) no ticks are present, or (2) the tick population is lower than it ought to be. These cases can be explained on grounds of lack of opportunity for colonization (1); or colonization so recent that population has not attained the level of ‘dynamic equilibrium’ with the environment (2). The question of ‘spread’ (colonization) is discussed fully in the text. The sheep flock is the main agent in spreading ticks. Spread is comparatively slow and relatively small in extent nowadays. There has very probably been considerable increase both in tick population densities and in infested areas since the advent of intensive hill and moorland grazing with farm stock some centuries ago.

The reactions of the house-fly larva to four environmental factors, namely temperature, air humidity, smell and light have been studied in the Laboratory. It was hoped that the results would shed some light on the general behaviour of the larva in its normal habitat. A comprehension of this behaviour will assist in understanding the ecology of the species, and hence facilitate its control. In order to analyse the behaviour of the larva, its reactions (other than to light) were first studied in relation to one factor at a time. An attempt was then made to test experimentally its reactions to various combinations of factors.

1. Two specimens of Coenurus serialis in the rabbit are described.

2. The duration of infection is estimated at 18–24 months.

3. Secondary external daughter coenuri had developed within the same adventitious cyst of host tissue as the primary coenuri.

4. No internal daughter coenuri were found within the primary coenuri.

5. Both primary coenuri contained some scolices which had developed vesicles (ranging from 3 to 30mm.) in their ‘neck’ region. These vesicular scolices remain attached to the germinal layer until the vesicle is 4–5 mm. in diameter, when they become detached. These would appear to be the internal daughter coenuri of many authors but are here shown to be degenerating scolices.

The descriptions which have been given by travellers leave no doubt that land-leeches can cause considerable annoyance, and that the protective garments and substances that were applied by them to the skin and clothing were unsatisfactory. It was thought that other and more elaborate clothing would not supply the answer, as they would be hot and uncomfortable to wear. Accordingly, a search was made for an efficient repellent. Altogether seventy-eight substances were examined, and of these hydroxycitronellal was the most powerful but expensive and not readily obtainable. Di-methyl phthalate was efficient and the most generally useful. As di-methyl phthalate is a liquid which easily escapes from containers, creams incorporating the substance were evolved. Formulae for these creams are given.

1. The introduction refers to the fragmentary state of our knowledge on Trombiculid mites and indicates that most attention has been devoted to the taxonomy and bionomics of the group. The life cycle and general method of feeding are briefly outlined and reference is made to previous work directly concerned with the present treatise.

2. The morphology of the organs related to the phenomenon of piercing and sucking in the larva of Trombicula autumnalis is described.

3. The physical factors of the skin influence the choice of habitat upon the host.

4. The food consists of tissue fluid and disintegrated cells of the malpighian layer partially liquefied by the action of injected saliva, a condition typical of extra-intestinal digestion.

5. The mechanism of the initial piercing of the skin, which is done by the cheliceral claws, is described.

6. A tubular tissue canal is gradually formed in the skin of the host and around its insoluble wall are deposited superimposed layers of keratinized protective tissue.

7. The mechanism of suction is described and the factors which play a part are considered. The problem of the tissue canal serving as a duct for both the ejection of saliva and the suction of food is explained by the alternation of the two processes. The inter-relationship, between the intermittent injections of saliva, the formation of the tissue canal and the deposition of protective tissue, is elucidated.

Trombicula tamiyai and T. fujigmo n.sp. are described and figured from Japan and northern Burma respectively; the holotypes are in the U.S. National Museum. The first, unnamed or referred to European autumnalis, has previously been illustrated and discussed by some Japanese authors with T. japonica Tanaka et al., under the term Japanese harvest mites (‘akidani’). Figures of T. japonica are also provided here for comparison. Reared nymphs and adults are reported by the Japanese as unusually elongate for trombiculid mites. Figures of the elongate nymphs are comparable with that given by Hirst for T. autumnalis, the European harvest mite, the adult of which is likewise elongate. Should further data, including rearing, indicate the need for generic separation of this group of ‘harvest mites’ from Trombicula, then Neotrombicula Hirst would apply. Specific characters for other apparently related species are tabulated and discussed.

It is generally accepted that the various species of Leishmania of men and dogs are morphologically indistinguishable. Therefore it has been argued that, according to the present rules of taxonomy, they should all be included in one species, L. donovani (Laveran & Mesnil, 1903), Ross, 1903. A review of the literature indicates, however, that this view is not generally acceptable, while strict adherence to the morphological rule would require the inclusion of the Leishmania of lizards (L. hemidactyli, L. agamae, etc.) in the same species as those of men and dogs.

It was noticed that some stock cultures of Laemophloeus minutus Olivier and L. ferrugineus Stephen were showing an abnormally high mortality. The numbers of living larvae appeared to decrease, many pupae died inside their cocoons and most of the few adults which emerged died within a few weeks. As adult Laemophloeus live for about 6 months at the conditions under which the cultures were kept (25° C. and 70% r.h.) it was apparent that something was killing the beetles at all stages in development. Microscopic examination of dead larvae and adults which had been chopped up and mounted in Berlese's fluid (Swan's formula) revealed huge numbers of the lemon-shaped spores (sporocysts) or pseudonavicellae of a sporozoan parasite. Living larvae from infected cultures were dissected in saline, and smears were fixed in Bouin's fluid (aqueous) and stained with Heidenhain's haematoxylin. Other larvae were fixed in Bouin's fluid, sectioned, stained with Ehrlich's or Heidenhain's haematoxylin and eosin, cleared in xylol and mounted in Canada balsam. These preparations revealed various stages of a schizogregarine which appeared to be Mattesia dispora which was described by Naville (1930) from Ephestia kühniella Zell. (Lepidoptera, Phycitidae) and recorded by Musgrave & Mackinnon (1938) from Plodia interpunctella Hbn. (Lepidoptera, Phycitidae). Careful examination of sections and measurement of various stages confirmed this identification. All stages were found, with the possible exception of young gamonts formed by macronuclear schizogony.

The plerocercoid larvae of Grillotia heptanchi (Vaulle-geard) used in the present study were obtained from the right supra-orbital lateral line canal of a specimen of Merluccius merluccius (L.). Two larvae were located in the canal in the region of the frontal bone and two in the region of the nasal. All were alive and were found to expand and contract slowly on removal. Unfortunately, the exact locality from which the fish came is not known as it was obtained from a fishmonger at Cardiff, but it is fairly certain that it was caught off the west coast of the British Isles.

The specimens of this new species of mite were collected by Mr Gordon Thompson, formerly curator of the Science Museum of the Institute of Jamaica, from the legs of a specimen of the golden thrush, Turdus aurantiacus Gmelin, taken at Morant Bay Road, 14½ miles east of Kingston, 14 January 1947. The bird was a male, and in a letter dated 11 March 1947 he says the mites were ‘extracted from a “growth” after macerating it for a while in caustic potash. This is the only “growth” of its kind I have found among approximately two hundred birds examined in Jamaica. The bird seemed quite healthy.’ I have to thank Mr Thompson for his kindness in handing me this, together with other acarine material, for study and determination.

The present paper is mainly concerned with the records and descriptions of new species of parasitic acari obtained in Ceylon and sent to me during 1947 by Mr Gordon B. Thompson, of whose collection they form a part. The study of the specimens of the tropical rat mite, Echinolaelaps echidninus (Berl.), represented in this material led me to re-examine both the literature and the specimens of this species contained in my own collection, and I have included in the present paper the results of this investigation and have established various forms of the species which this necessitates besides showing the probable relationships existing between them.

1. In a mixed infection in which Haemonchus contortus, Ostertagia circumcincta and O. trifurcata predominated, the lengths were plotted against widths of eggs obtained from faeces.

2. Two-dimensional groups approximating to normal frequency distributions, showing little overlap, were observed.

3. The statistical ranges of means plus and minus twice the standard deviation for the two groups barely touched. These were, to the nearest micron, 68–84 by 41–51 for Haemonchus contortus and, for the Ostertagia group, 83–103 by 46–52.

Most of the nine species dealt with in this paper were collected before the outbreak of World War II. Library facilities in Ceylon, meagre enough even in normal times, were altogether unavailable during the war years owing to the removal of the Colombo Museum Library to safe areas inland. It was only after the library was brought back to Colombo at the beginning of 1947 that this paper could be got ready for publication. Hence it appears 10 years after the last contribution in the series.

In the course of studies of copepods parasitic on the market fishes of South India two of the most valued fishes, Scomberomorus commersoni and Stromateus niger, were found infested by large numbers of the blood-sucking parasites, Pseudocycnus armata Bas-sett-Smith and Lernanthropus konigii Steenstrup & Lutken. In the present paper the description of Pseudocycnus armata, which was first recorded by Bassett-Smith from Bombay and later by Kirtisinghe from Ceylon, is confined to a more accurate account of the appendages than has been given by these authors, while Lernanthropus konigii, which has not been recorded since it was established in 1861, is fully described.

1. Spermatophore production in Rhodnius and Triatoma is a structural adaptation for copulation and sperm delivery.

2. In Rhodnius a certain amount of sperm is stored in the spermathecae while the remainder is ejected with the collapsed spermatophore about 12 hr. after copulation. Hypergamesis never occurs.

3. The secretion in the male accessory glands was found to disappear if males were kept unfed for about 60 days. Such males were unable to copulate.

4. An average of ninety-eight fertilized eggs was produced as a result of one insemination by a young male. Four such inseminations at intervals of 45 days are, therefore, necessary to secure fertilized eggs throughout the entire life of the female. In nature repeated copulation is the rule.

5. The first spermatophore produced by males starved for 21–28 days was found to be as efficient as that produced by recently emerging well-fed males.

6. A male is capable of producing a great number of spermatophores; as many as fifty were obtained. Probably spermatophores produced by old males, although they contain a great number of sperm, lack sufficient of some substance necessary for fertilizing the eggs.

A method for comparing the lethality effect of contact insecticides on mosquitoes and house-flies is proposed.

It is based on the comparison of the death-rate and the length of survival of insects after a contact for a very short and exactly measured time with a surface sprayed with a known concentration of the insecticide.

It is suggested that the same method may be used to compare the susceptibility of various species of mosquitoes and flies to the toxic action of a contact insecticide.

Some of the methods and apparatus were worked out and constructed by the Staff of No. 1 Malaria Field Laboratory under the command of the senior author. The following Officers and N.C.O.'s of the Royal Army Medical Corps were especially active in this work, and acknowledgement is made of their valuable contributions: Major T. T. Macan, Major Fox, Lt. MacDonald, Staff-Sgt. (later Major) Iles, Cpl. Mortimer.

We are also indebted to Prof. F. S. Bodenheimer and Major T. T. Macan for their help in preparing this paper.