The coccidium of mice (Mus musculus) was discovered by Eimer (1870) who named it Eimeria falciformis. It is round or oval. According to Reichenow the round oocysts measure 13·5–15μ and according to Reimer (1923) 14–18·9μ The oval oocysts measure 13–14×8–9μ or 16–21×11–17μ A residual body may, or may not, be present in the oocysts, but is present in the sporocysts. There is no polar granule in the oocyst.

1. A progenetic metacercaria of Phyllodistomum lesteri sp.nov. is found encysted in the fresh-water shrimps, Palaemon asperulus von Marten and P. nipponensis de Haan.

2. A systematic description is made of this new species including general characteristics of the family, subfamily and genus and a list of the existing 29 phyllodistomes.

3. In general, the new form resembles Pleurogenes medians with regard to its progenetic development.

4. Feeding experiments suggest that two species of fish, Odontobutis obscura and Pelteobagrus fulvidraco, and a species of toad, Bufo bufo asiaticus, are not the final hosts of Phyllodistomum lesteri sp.nov.

Eupelmella vesicularis Retz. was found in certain parts of Hungary infesting cocoons of Diprion sertifer Geoff. already parasitized by a primary parasite, Microplectron fuscipennis Zett. It was never found in the absence of this chalcid.

Experiments showed that Eupelmella confined itself almost exclusively to Microplectron as a host, easily detecting the presence of larvae or pupae of this parasite within the cocoons of the saw-fly host, but neglecting eggs.

A single egg is laid per cocoon and the larval Eupelmella eats from 10 to 20 Microplectron larvae or pupae, and finally kills all the remaining living parasites within the cocoon before pupating.

The egg and larva show interesting structural adaptations for this mode of life.

Reproduction is parthenogenetic and no males are known.

Several factors combine to make this insect a dangerous enemy of Microplectron capable of seriously impairing its efficiency. These are: its selective ability, its destructive powers, its rapid rate of increase due to the parthenogenetic habit, and its ability to establish itself and survive on small numbers of the prey, for the same reason.

Numerous specimens of this fluke were collected in October 1936 from the small intestine of the Bonell's eagle, Hieraetus fasciatus fasciatus, shot in the vicinity of Allahabad. Only one out of six hosts examined was infected. The sexually mature worms, 1·171–2·622 mm. long, are distinctly divided into elliptical forebody and cylindrical somewhat posteriorly pointed hindbody. The forebody, 0·969–1·236×1·186–1·476 mm., with foliate lateral margins united behind the holdfast Organ, is armed with very minute, backwardly directed spines; the hindbody is 1·2–1·386×0·634–0·818 mm. The length ratio of fore and hind parts is approximately 6:7.

This trematode was obtained from cockles brought up with mussels to the Conway Mussel Cleansing Station and also from cockles collected from several other localities on the Menai Straits. It was present in every cockle examined, a total of several thousand in all. It occurred as a brown mass of varying size situated immediately beneath the hinge and occupying a small wedge-shaped cavity which occurs there. It could be obtained by cutting away the hinge with a knife when the brown mass was exposed. The latter breaks up very easily on teasing and consists of numerous more or less oval thick-walled sporocysts loosely embedded in the tissue of the cockle. These sporocysts are colourless or slightly straw-coloured and immobile. They contain a varying number of cercariae and a considerable amount of granular brown material. The fully developed cercaria (Fig. 1) is transparent except for the excretory sacs, which are full of very highly refractive granules and appear dark. The maximum diameter of these granules has been put forward by Rothschild (1935) as a valuable diagnostic character; in this species it is 5μ. The cercariae are moderately active and survive some time in sea water after removal from the sporocyst. This trematode was found throughout the year.

A report is made of nine cases in which Diploscapter coronata was found, in great abundance and in all stages of development, in human stomachs containing little or no hydrochloric acid. A critical review is given of the literature of parasitism of vertebrates by rhabditid worms, and it is concluded that these worms may establish themselves and multiply in diseased female urino-genital systems as well as in hypohydrochloric stomachs, and may live as larvae in the skin, particularly when this is mangy, or multiply on the surface of the skin, but that the evidence of establishment in the intestine or respiratory system of mammals is still inadequate.

A flagellate of the genus Bodo is described, which was found in the faeces of a man on 4 occasions during a period of 12 days, sources of extraneous contamination being excluded from the last 3 specimens. Although morphologically it is identical with Bodo, it differs from other known members of this genus in that it multiplies more readily at 37°C. than at lower temperatures.

During the spring, summer, and autumn of 1935 and 1936, bi-weekly collections of invertebrates were made in the chicken yards of the Zoological Division Field Station at Beltsville, Maryland, U.S.A. Among a miscellaneous group of insects found near a feed trough on 15 July 1935, was a small beetle, Litargus sp. This insect contained two specimens of a peculiar bristly cysticercoid. In September 1936, five beetles, Alphitophagus bifasciatus, collected in the same chicken yards, each contained from 1 to 8 of these larval cestodes. Additional specimens of what appear to be the same cysticercoid were collected by Dr H. L. Van Volkenberg (1931) (U.S. Nat. Mus. Helm. Coll. Nos. 41673 and 41672) on 10 July 1934 and 4 April 1935, respectively, from Ataenius stercorator at Mayaguez, Puerto Rico. A comparison of both in toto mounts and sections of the specimens from Puerto Rico with those from Maryland showed that the larval cestodes are identical. The name Cysticercus setiferus is proposed for this species.

1. The paper discusses the points of difference between the three larval instars in Pediculus and the changes in proportion which take place during growth, not only during larval life but also at the final moult.

2. It is easy to separate larvae of the first instar from others, more difficult to distinguish those in the second and third instars. The principal points of difference are as follows:

First instar. Setae on dorsum of abdomen, few, long and in longitudinal lines: one median pair on most segments. Paratergal plates (carrying spiracle) absent. Mean measurements as in Table I, the best point of distinction between instars being in length of third tibia, which is 0·197 mm. in first instar. Ratio of head to thorax and abdomen about 1:2·8

Second instar. Setae of dorsum of abdomen in one transverse row, containing 2–3 pairs of setae. Paratergal plates present (as also in third instar). Mean length of third tibia, 0·270 mm. Ratio of head to thorax and abdomen about 1: 3·5.

Third instar. Setae on dorsum of abdomen, not in one row, but somewhat irregular: a pair of minute supplementary setae, on seventh and eighth segments, close to midline. Mean length of third tibia, 0·363 mm. Ratio of head to thorax and abdomen about 1:4·3.

3. During larval life the dimensions of all parts increased as geometrical progressions (Dyar's law), but the rate of increase is different in different parts of the body, so that the proportions, for instance, of head to thorax and abdomen alter with growth; in other words, growth is allometric or heterogonic. But when the insect attains maturity the measurements of several of the parts depart significantly from the geometrical progression which has prevailed during larval life. In most parts of the body the increase at maturity is greater in females than males (no point of distinction having been observed in larvae in the preceding instars); but in the length of the third tibia the increase in the female is much less than in the male. Among other insects in which metamorphosis is slight there are several in which the rate of growth of parts alters at the last moult and becomes different in the two sexes; in some indeed the difference develops much earlier than the last moult. Probably, therefore, it would be true to say that regular allometric growth is generally disturbed by the development of secondary sexual characters.

It is a pleasure to acknowledge help received from Dr J. S. Huxley.

1. The material which is discussed in the present paper consists of more than 2000 crops of hair collected from Sokoto, Nigeria; Nairobi and Kakamega, Kenya; Colombo, Ceylon; and Jerusalem, Palestine. The amount of material examined is considerable, but it must be admitted that it has not been found possible to obtain an unselected sample representative of any human community as a whole.

2. The paper gives detailed information about the prevalence of head-lice in respect of the individual's race, sex, age, weight of crop of hair and the season of the year.

3. The following general conclusions may be drawn:

(a) The distribution of lice among a population of people is skew. Among infested persons the commonest count is always low (generally 1–10 lice), but occasional counts of many hundreds or a few thousands are recorded.

(b) If the people are grouped by age, sex, etc. a positive correlation is generally found between the proportion of men in each group who are infested and the mean number of lice per infested person.

(c) There is clear evidence from several places that season affects the frequency of infestation. In most but not all places the insect is most widely distributed in the colder, wetter part of the year. It is not known whether this is due to some effect of climate upon the insect itself or upon human habits and activity.

(d) It will doubtless be found that the individual's race is an important factor in determining infestation, but little has yet been established on this subject.

(e) Wherever material has been available from individuals of widely different age, it has been found that boys are more infested than youths, who in turn are more infested than grown men.

(f) In some places females are more frequently infested than males, though it was established that there was no difference between the sexes at Kakamega.

(g) The weight of the individual's crop of hair is in most places positively correlated with infestation.

4. Many of the factors mentioned in 3 (d)–(g) are local and depend on racial customs. It is emphasized that further investigations would be most profitably carried out in the countries concerned by men well acquainted with the local people and their ways.

5. There are probably a large number of individual differences due to sensitiveness, vanity, general health, etc.; these have hardly been studied at present but it is probable that collectively they are very important.

The purpose of this work has been to identify and describe the immature forms of those species of tachinids which have occurred as parasites of Pierisrapae and P. brassicae at the Imperial College Field Station, Slough, Bucks.

The following animals are from a collection made for and kindly presented to me by Miss Nora G. Sproston during her visit to the Station Biologique de Roscoff, Finistère, in June 1937.

In Plasmodium gallinaceum, parasitic in domestic fowls, in addition to the schizogony in red blood corpuscles, schizogony also occurs in monocytes and cells of the reticulo-endothelial system. This schizogony in cells other than erythrocytes may be termed, for convenience, exo-erythrocytic schizogony.

Exo-erythrocytic schizonts are characterized by never having malarial pigment (as they live in cells devoid of haemoglobin), by growing to a large size and forming numerous merozoites, up to 50 or 60 or even more.

Exo-erythrocytic schizonts are not confined to leucocytes of the blood stream, but can also develop in fixed endothelial cells of organs such as the brain, lung, liver and spleen.

The brain is an especially important focus of development and, after sporozoite infection, it is the first organ in which exo-erythrocytic schizonts develop. These schizonts may be found in capillaries of the brain as soon as parasitized erythrocytes are present in the peripheral circulation, but as yet they have not been found before parasites-are present in the peripheral blood.

In the brain rows of schizonts may develop and ultimately occlude most of the capillaries in the brain. This blockage of capillaries results in symptoms of general paralysis in the infected birds and death follows in a few days; and it frequently occurs in birds which apparently have been cured of the peripheral infection by treatment with quinine.

The exo-erythrocytic stages of P. gallinaceum occur in birds which have been inoculated with blood or with sporozoites.

During growth, the body of the schizont breaks up into a number of masses or cytomeres, on the periphery of which the merozoites are developed on regularly arranged rows of digitiform processes. A mass of chromatin migrates to the distal end of each process and is cut off to form a merozoite.

The mature schizont consists of a mass of irregular merozoites enclosed in a sac-like membrane which may be the remains of the host cell. The merozoites are composed almost entirely of chromatin and when they are fully developed practically no cytoplasm of the schizont remains.