Anopheles elutus females are attracted by human beings. The human body eliminates certain substances which exert an attraction. The expired air alone is sufficient to attract the mosquitoes. Mild air currents may play an important part in carrying and directing these attracting factors towards the mosquitoes.

In a former paper (Baylis, 1944) an account was given of some observations on the life-history of Mermis nigrescens, and of its occurrence, naturally and experimentally, in earwigs (Forficula auricularia). As stated in that paper, the material then available did not seem to warrant an attempt to describe the larval development. Further material has now been obtained and studied, and it seems desirable to place on record some of the observations made, although many points still remain obscure.

All the Mesostigmatic mites which have been found as ecto- or endoparasites of snakes are listed and it is suggested that the latter are probably derived from the former. The homologies of the dorsal shields are established and a progressive fusion is shown to have taken place. On this evidence a new genus is erected for O. bedfordi (Radford) to include most probably the lung mites of African snakes. The life history and general biology are discussed. It is shown that there is no experimental evidence that these acari are vectors of disease or that they induce any change in the tissues of the host. Evidence is brought forward to show that the parasites of the more nearly related snake hosts are themselves more nearly related: some consequences of this are discussed. A key to the females of all the known lung mites of snakes is given together with the diagnosis of the new genus Hammertonia and of a new species, Ophiopneumicola americana. The view that the genus Ophiopneumicola is not a natural group is expressed. O. hammertoni Radford is redescribed and some points of significance discussed. The species incertae sedis of Keegan (1943) are discussed.

The idea has been mooted that the sheep tick (Ixodes ricinus L.) is active at different times on different host species. Tick-activity curves for sheep, deer, hare, rabbit, skylark and meadow-pipit are similar in form and timing. With these animals, therefore, there is no indication of any marked individual species effect on activity.

Where spring activity occurs, males, females and nymphs usually have similar and concurrent activity curves, but nymphs may occasionally have their peak 2–3 weeks later than adults. Larval activity is always later, the peak being several weeks after the female peak. The data for nymphs amend the general statement on activity in a previous paper by the present author.

Ticks are active during the hours of darkness but the activity-density then is considerably less than in daylight. This diurnal fluctuation in activity seems to follow fairly closely the diurnal fluctuation in atmospheric temperature.

In general, female ticks infest the hairy areas of sheep: head and legs; the (comparatively) bare areas: axillary and inguinal; and certain woolled areas: chiefly the short-woolled margins of the hairy and bare areas; they do not attach in the long wool of withers, back, rump and flanks.

More female ticks attach on the head than on the axillary region, and more on the axillary than on the inguinal region, obviously on the principle: first come best served.

Different tick stages tend to attach in different zones of the same regions; two theories are put forward to account for this.

On a hill pasture where the main tick activity occurs in spring only, the average totals of female ticks carried per annum by ewe, hogg and lamb were in the proportions 8:6: 1. Host size is thought to be the chief governing factor.

Under existing British hill pastoral conditions, the upper limits to female tick infestation appear to be of the following order: average spring peak total count per ewe reaches 100–150, with extreme individual limit about 300; and about five times as many ticks are carried per ewe over the entire spring season.

On heavily infested hill pasture, stocked at one sheep to 1–5 acres, typical flocks feed from 100 to 600 female ticks per acre per annum. The densest sheep stocking results in the highest tick density.

For every one female tick, about eight nymphs were fed by sheep in one season.

The better the condition of a sheep, the less bare of wool and apparently (to touch and sight only) the more greasy, and the lower the tick infestation.

In any age group of sheep on one grazing, there is considerable range in weekly infestation weights but individuals tend to keep their relative positions consistently in this range. Sheep differing markedly in their infestation weights show a remarkable lack of difference in the majority of physical and physiological characteristics of body form and body surface. (Fleece humidity was omitted from study.) Notably, there is no indication of significant differences in fleece greasiness. Apparently only two characteristics go with the lighter infestations in Blackfaced sheep. These are coarser fleece hair and less clearance between fleece tips and ground, having doubtful and minor effects respectively.

The most important factor in individual differences of infestation within an age group is very probably individual activity, i.e. the more ground covered in unit time, the more ticks picked up.

In Britain the genus Psychoda Latr. contains sixteen species and two subspecies (Kloet & Hincks, 1945), the larvae of which occur in cow dung, decaying vegetation, and the bacteria beds of sewage purification works. A knowledge of these larvae would be useful both to the sewage biologist and the sanitary inspector, but for only three species have the larvae been fully described. Two of these, Psychoda alternata Say, and Ps. cinerea Banks, are inhabitants of the bacteria bed, and the larva of the former has been described on at least six occasions, the classical account being that of Dell (1905). The larva of Ps. cinerea has been described three times, the most complete account being that of Malloch (1917). The third Psychoda larva of which we have a full account is Ps. albipennis Zett. (Keilin & Tate, 1937), a species inhabiting dung and decaying vegetation. In addition to the foregoing there is a brief and inadequate description of the larva of Ps. severini Tonn. (Johnson, 1914), a species which is commonly present in the bacteria bed.

In recent work on the deposition of the epicuticle, Wigglesworth (1946) has shown that, in Rhodnius prolixus, not only is the epicuticle a composite structure comprising several distinct layers, but that the pore canals, which hitherto have been believed to terminate at the base of the epicuticle, do in fact penetrate its innermost regions. Wigglesworth extends the term epicuticle to cover the four outer layers of the cuticle in Rhodnius. The innermost of the four is a cuticulin layer which is followed by a polyphenol layer, a wax layer and an outer cement layer respectively. The pore canals penetrate the cuticulin layer.

A consideration of the tick-activity data for South Wales reveals that there are usually two peaks of female activity in this region, one occurring in spring, the other in autumn. On an experimental area, divided into eight plots, on the Margam Moors, Glamorgan, significantly varying population levels are present on the different plots, although the peak of activity on all of them is attained around the same period. The seasonal activity of the nymphal and larval forms in South Wales is essentially comparable to that recorded by Milne (1945a) in the north of England. There is reason to believe that in mid-Wales a single summer peak of tick activity exists.

The engorgement period of female ticks on cattle varies from 7 to 13 days. The tick shows a distinct preference for the hind region of cattle for feeding purposes. The differences in the mean populations of ticks on different breeds of cattle are not statistically significant, at least, on the six breeds tested in 1944 and 1945. In the case of cattle, tick density and fecundity of the female are not correlated with the physiological condition of the host.

In South Wales, the populations of ticks on sheep are significantly lower than those on cattle, even where both hosts are pastured on the same ground for similar periods. The seasonal activity of female ticks on horses follows the same general trend as that noted on cattle.

The two filarial Nematodes known to parasitize dromedaries in Egypt are Dipetalonema evansi and Onchocerca fasciata, of which the first is the more common. Representatives of these genera also infect man and other animals and are known to be very common in endemic areas. Doubt has always arisen in the researches of those few who worked on this subject, as to the connexion of the adult Dipetalonema evansi with the microfilariae found in the blood of Camelus dromedarius and C. bactrianus.

The material used for the following description consisted of three worms obtained from the intestine of the oystercatcher, Haematopus ostralegus occidentalis Neumann, shot near Aberystwyth. This is the first record of a protogynous tapeworm from Britain. In the whole of the Cestoda the protogynous condition is known only in four other genera, namely, Progynotaenia Fuhrmann (1909), with six species, and Proterogynotaenia Fuhrmann (1911), Leptotaenia Cohn (1901) and Gynandrotaenia Fuhrmann (1936, 1936a), each with a single species. The six known species of the genus Progynotaenia have been recorded from Egypt and the White Nile, Proterogynotaenia rouxi Fuhrmann from the Aru Islands off the coast of New Guinea, Leptotaenia ischnorhyncha (Lühe) from the Mediterranean and Gynandrotaenia stammeri Fuhrmann from Germany.

(1) Ecdysis of the infective larvae of Trichostrongylus retortaeformis was induced by the action of pepsin.

(2) Exsheathment occurred by the loss of the anterior cap.

(3) pH 4−5 is shown to be the most favourable pH for eedysis and survival. This pH is within the range quoted for the stomach contents of rabbits.

(4)Eedysis was complete in the majority of larvae after 60 hr.

Four specimens of the pika (Ochotona rufescens Gray) were captured, and on dissection three of them were found to be heavily infested with a Nematode worm in the large intestine.

1. Stained specimens of two forms of a ciliate parasite resembling Lambornella stegomyiae Keilin which is probably Glaucoma pyriformis Ehrenberg are discussed. These were collected from the haemocoel of culicine mosquito larvae at Livingstone, Northern Rhodesia. The form previously referred to as type A (Muspratt, 1945) is the fast multiplying form which destroys the larva and that referred to as type B is considered to be either an encysting or degenerate form.

2. In nature the larva of Aëdes (Finlaya) fulgens Edw. is the most suitable host of the parasite because the normal (type A) parasitic ciliates are dependent on escaping from the larval host before death by the rupture of the anal papillae. This occurs most frequently in parasitized larvae of the above species.

3. The encystment of the organisms on the cuticle of the larvae is discussed with reference to statements by previous workers. Stages in the penetration of the cuticle by the organisms and the formation of cuticular resting cysts have been observed.

4. Larvae of A. aegypti used in laboratory experiments proved to be unsuitable as: (a) The anal papillae do not rupture easily. (b) After some time the reproductive power of the ciliates degenerates if they are transmitted from larva to larva of this species only.

5. Attempts to destroy anopheline larvae with the parasite were negative although the ciliates entered the haemocoel.

6. A suggestion as to the possible life-cycle is appended in the form of a diagram.