1. Histomonas meleagridis was isolated in culture from the liver lesions of a hen suffering from “blackhead” (enterohepatitis). It has been cultivated at 36·5–37°C. for over a year.

2. Chicks, which had been reared free from protozoa, were inoculated per os or per anum, with cultures of the above strain of H. meleagridis. Eleven out of twelve birds became infected. Caecal lesions only were produced. This strain, although isolated from the liver lesions of a hen suffering from acute blackhead, showed no abnormal virulence in chicks.

3. Individuals of this strain of H. meleagridis showed amoeboid movement but were also flagellate. Normally the protozoon was uninucleate, but binucleate forms were common, and tri- and quadrinucleate forms occurred more rarely. One flagellum arose from each nucleus.

4. During division the flagellum disappears. The method of nuclear division was similar to that of Trichomonas.

5. A resistant phase was never seen in the cultures.

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.

Various stages in the life cycle of Panopistus pricei are reported from Agriolimax agrestis. These are essentially the same as those reported by Krull from Zonitoides arboreus. The excretory system of a developing metacercaria is described.

When eggs of Monieza expansa are fed to galumnid mites, the onchospheres emerge in the intestine and migrate to the body cavity. Here they undergo metamorphosis and develop into cysticercoids. The dissection of mites, at various intervals after exposure, has yielded a successive series of developmental stages. Protocols of the experiments and photographs of living larvae are presented. These results demonstrate that mites serve as intermediate hosts of Moniezia, and probably also of other anoplocephaline cestodes.

During a study of syrphid larvae I met with several instances of their being parasitized by hymenopterous larvae. The species of syrphid larvae most commonly parasitized, in my material, was Sphaerophoria flavicauda. From the puparia of this species I obtained two species of ichneumonids, which Mr J. F. Perkins, of the Natural History Museum, London, very kindly identified for me as Bassus tetragonus Thunb. and Homocidus fissorius Grav. Out of seven puparia of Sphaerophoria flavicauda, one adult of Homocidus fissorius and six of Bassus tetragonus were obtained. This paper therefore deals mainly with the larvae of the latter species.

The effect of an efficient bactericidal solution on the hatching of Haemonchus eggs was studied and it was found that a large proportion remained viable. Based on former work, a medium was devised in which the bacteria-free eggs hatched and the larvae developed to the infective stage. These larvae were morphologically and otherwise normal, except that they were slightly smaller than faecal-grown specimens, although the size ranges overlapped. Infection tests proved that Haemonchus larvae grown under conditions of sterility were normally infective for, and produced normal adults in, a susceptible lamb.

1. The life-history of Entamoeba coli (from a marmoset, several macaques, and Man), as observable in cultures, is here described and illustrated. It is found to be similar, in general outline, to that of E. histolytica, but to differ considerably in its excystation and metacystic stages.

2. At excystation, the entire contents of the cyst usually escapes, as a single multinucleate amoeba, through a large opening in the cyst wall, which is composed of two layers.

3. Normal ripe cysts frequently lose 1 to 4 of their 8 original nuclei before hatching, thus becoming “infranucleate” (i.e. containing only 4 to 7 nuclei instead of the “typical” 8).

4. During the metacystic stages no nuclear divisions occur. The hatched amoeba eventually produces, by a series of binary cytoplasmic fissions with random nuclear distribution, as many uninucleate amoebulae as it originally contained nuclei.

5. An originally 8-nucleate cyst may therefore produce 8 amoebulae finally –never more: but owing to the frequent development of infranucleate forms, it often produces only 7, 6, 5, or 4.

6. Development is complicated by occasional division into two within the cyst before hatching, or at the moment of hatching—such divisions being seen in both “typical” and “infranucleate” cysts; and also by the occurrence of supernucleate cysts (containing more than 8 nuclei), which are often viable but usually develop in an infranucleate condition. Consequently, amoebae containing any number of nuclei from 1 to 8—or even more—may hatch from the cysts of this species (unlike those of any other hitherto described).

7. The uninucleate amoebulae resulting from the metacystic divisions are young trophic amoebae—not gametes—and no sexual stages occur in the life-cycle. Division of the trophic amoebae is briefly described and figured.

8. The life-cycle of E. coli is finally compared with that of E. histolytica and related species: the relevant observations of other workers are briefly analysed: and the taxonomic implications are noted.

A memorandum is added on the genus Entamoeba, in an attempt to clarify the nomenclatural and taxonomic confusion created by Opinion 99 promulgated by the International Commission on Zoological Nomenclature. This leads to the conclusion that the Opinion itself is a dead letter, though the genus Entamoeba still lives and should therefore be retained, for the time being, with E. coli Casagrandi & Barbagallo, 1895, as its type.

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.

1. Several behaviouristic and physiological differences distinguish the two species Trichogramma semblidis and T. evanescens (tabulated on p. 514).

2. There are no true intermediates between the two forms of the male T. semblidis, but intermediate types are simulated by degenerate individuals of small size produced by starvation.

3. Among 1740 males reared from eggs of Sialis and 1847 reared from eggs of moths, there were only nineteen exceptions to the rule that the apterous form emerges from the former and the winged form from the latter.

4. The ability of T. semblidis to produce its apterous male can remain latent through as many as sixty-four generations reared on Sitotroga and yet find its full expression immediately when the parasite is reared on Sialis.

5. Several other species of Neuroptera have been parasitized, but Sialis lutaria remains the only known host that regularly elicits the apterous form.

6. T. semblidis is capable of arrhenotokous parthenogenesis. The statement that the species includes thelytokous strains requires corroboration.

A Collection of ticks from British Somaliland recently sent to the British Museum (Natural History) contained specimens of a species of Ornithodoros unlike any in the national collection and (from the appearance of the integument) related to the North African species O. foleyi Parrot (from Algeria) and O. delanoëi Roubaud & Colas-Belcour (from Morocco). The late Prof. G. H. F. Nuttall presented to the Museum a specimen of O. foleyi, and the writer is indebted to Prof. E. Roubaud for comparing one of the present specimens with the type of O. delanoëi. Prof. Roubaud writes to say that, having examined the Somaliland specimen, he and M. Colas-Belcour are of the opinion that it belongs to the species O. delanoëi: and that the various details of structural difference do not warrant a specific distinction, but indicate that the present specimens may belong to a different biological or geographical race. The large size of these Somaliland ticks, the discovery of their larvae and their presence in a locality so widely separated from that of the type, are considered important enough to be placed on record, and the specimens are regarded as representing a subspecies of O. delanoëi

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.

To students of the literature dealing with amoebic dysentery the name of O. Uplavici is probably not unfamiliar: but few authors are aware, apparently, of his singular story, so the following lines recording his life and death may therefore be acceptable to readers of Parasitology.

The species of Hymenolepis Weinl. described in the following pages was collected from the small intestine of a greater black-backed gull, Larus marinus, shot on the Dovey mudflats near Aberystwyth, in February 1935. Comparisons of the dimensions of scolex and strobila, measurements of rostellar hooks and suckers, and appearance of genitalia, prove beyond doubt that the species is identical with that described by Linton (1927) under the name of Hymenolepis fusus (Krabbe) (vide Table infra). From the data tabulated in the discussion below, the writer is satisfied moreover that the species described by Linton is totally distinct from Taenia fusus Krabbe 1869, and the new name Hymenolepis neoarctica is therefore proposed to include Linton's species. Since the description by Linton dealt only with the morphology of the immature forms, the following account of the morphology of the mature worm is given, based on material collected at Aberystwyth.

The morphology of a micro-organism, Cytœcetes microti, new genus, new species, which invades the granulocytes and occasionally the lymphocytes, is described. It occurs naturally in the vole, Microtus pennsylvanicus, is transmissible to white-footed mice, Peromyscus leucopus and Peromyscus eremicus, the common tame mouse, the white rat, but inoculations of guinea-pigs. domestic rabbits, a kitten and young chickens have resulted negatively. The only pathological effect attributable thus far to this organism is an increase in the number of granulocytes found in certain organs such as the spleen and adrenals, and degenerative changes in the individual cell invaded. Splenectomy performed soon after the microscopic disappearance of Cytœcetes from the circulating blood may result in its reappearance, when it may occur in a considerable proportion of the granulocytes, but nevertheless in smaller numbers than at the height of early infection. Overwhelming infections have in no instance followed splenectomy. The probable relationship of the organism to Ægyptianella pullorum (Carpano, 1928) is pointed out, but grounds for placing it in a separate genus are presented.

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. Pimpla ruficollis is a parasite of the pine shoot moth Rhyacionia (Evetria) buoliana Schiff. (Eucosmidae) which emerges from its host a considerable time before the next generation of larvae are ready for oviposition. It seems that during this period the parasites leave the pine trees and feed on the flowers of certain Umbelliferae and probably other plants. Only after 3 or 4 weeks do they return to the pine trees where the shoots now contain larvae ready for egg laying.

2. It has been shown by means of olfactometer experiments that during this first period of the adult life, the parasites are repelled by the odour of oil of Pinus sylvestris. At this time the ovaries are very small and are probably not ready for the production of eggs. After the third or fourth week of life the females become attracted by the oil of P. sylvestris and the ovaries are now relatively large.

3. Since Geraniol is known to be a constituent of certain conifers, this substance was also tested. It was, however, found to be invariably repellent to the parasites.

4. There is some evidence that conclusions reached as a result of experiments with P. ruficollis also apply to the ophionine ichneumonid Eulimneria rufifemur.

An account is given of two aberrant strains of Trypanosoma evansi recovered from Sudanese camels.

One of these—like the four other ones described in a previous paper—was totally akinetoplastic (= akinetonucleate) and has been kept under observation for eighteen months in the course of which the aberrant condition remained unchanged.

The second strain was characterized by a wide fluctuation in the proportion of akinetoplastic forms which ranged from zero to over 70% at different periods of observation.

The bearing of this fluctuation upon the production of akinetoplastic strains is discussed and it is concluded that these probably arise in nature either indirectly, through the inoculation by the insect vector of new hosts with trypanosomes lacking the kinetoplast, or directly, by the strain becoming totally akinetoplastic within the same host.

From an analysis of the fluctuating strain it would appear that the variation in the proportion of akinetoplastic trypanosomes depends upon the following factors: (1) irregular division (without bipartition of the kinetoplast), which is the most important factor; (2) rate of reproduction of normal and aberrant individuals; (3) mortality rate of the different types of dividing and non-dividing forms.

The primary cause of the disappearance of the kinetoplast could not be ascertained.

The four new species of Macropostrongylus Yorke & Maplestone, 1926, and the one new species of Pharyngostrongylus Yorke & Maplestone, 1926, which are described in this paper formed part of a collection of nematodes obtained by the Australian Institute of Tropical Medicine, and forwarded by Dr G. M. Heydon to the British Museum (Natural History). Co-type specimens will be deposited in both institutions.

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.

Two mature worms of this species were recovered from the small intestine of a Common Snipe, Gallinago gallinago (Liun.), shot on a Cardiganshire moor in July 1935. Three mature worms were again obtained from a Common Snipe shot on the same moor in the third week of October 1936, just prior to the arrival of the migrant snipe.