This survey records the intestinal protozoa found in 611 hospital cases in Sweden, 1244 mental asylum cases in Sweden, and 159 medical out-patients in Finland. Only one examination was made of each case.

In each of these three groups the following protozoa were found: Entamoeba histolytica, E. coli, Endolimax nana, Iodamoeba bütschlii, Giardia intestinalis, and Chilomastix mesnili. In hospital and asylum cases in Sweden Dientamoeba fragilis was encountered, Trichomonas hominis and a small flagellate were found in the asylum group, and in this group as well as in the series in Finland, Balantidium coli was met with. In one case cysts of this protozoon were found.

In a group of 46 cases, formed stools as well as loose stools obtained after administration of a purgative were examined. The loose samples revealed the presence of Trichomonas hominis, Balantidium coli, and a small flagellate, none of these having been found in the formed specimens. The percentage of Dientamoeba fragilis rose from 8·7 per cent, in the formed stools to 23·9 per cent. in the loose stools. All the other species were more abundantly present in the loose than in the formed samples.

In Sweden, mental asylum cases show a much higher incidence of infections than do the hospital cases.

Intestinal protozoa seem to be more common in Finland than in Sweden.

Among hospital cases in Sweden the residents of Stockholm show a lower incidence of infections than do the people living in rural districts.

At admission, asylum cases are not infected to a higher degree than are the general hospital cases. The rise in incidence of infection is directly proportional to the length of time spent in the institutions up to ten years, after which time no further increase occurs. The male patients show throughout considerably higher percentages of infections than the female patients. Chilomastix mesnili shows a very high incidence in the asylums, whereas the percentage of Giardia intestinalis remains practically the same throughout the time of confinement in the institution.

A pure strain of Entamoeba histolytica has been isolated and cultivated, and an attempt has been made to study and describe its whole life-history in detail.

This strain (K. 28 c) was derived from the dysenteric dejecta of a kitten experimentally infected per os by means of typical cysts from the faeces of a monkey (Macacus sinicus). It has now been under continuous cultivation for about 20 months (220 serial subcultures), and its development in vitro has been uniform throughout.

Methods have been devised, and are here described, whereby any desired stage in the life-history of this strain—amoebae, cysts, and all intermediate stages (including encystation and excystation)—can be readily procured in vitro at will.

Detailed study has shown that the trophic amoebae multiply in cultures by simple binary fission only, as they do in their natural hosts. Their mode of division is briefly described.

Encystation also occurs in vitro just as it does in the bowel, with formation of characteristic precystic amoebae and the final production of typical quadrinucleate cysts.

Excystation has been carefully studied, and it has been found that a single quadrinucleate, amoeba escapes from each cyst through a minute perforation in its wall. An account is given of this remarkable process, which has not been described previously.

The 4-nucleate excysted (metacystic) amoeba has been found to produce a new generation of trophic forms by a complicated series of nuclear and cytoplasmic divisions, which are described in detail for the first time. The final result of this subdivision is the production of eight uninucleate amoebulae by each quadrinucleate amoeba hatched from a cyst.

These amoebulae are young trophic amoebae, and not gametes or conjugants. No sexual phenomena of any sort have been observed during the metacystic itages: and the life-history of E. histolytica, as visible in vitro, is thus wholly sexual.

A development similar to that here described in the case of Strain K. 28 c has been found to occur in many other cultivated strains of E. histolytica— including a strain isolated directly from man, and a human strain experiaentally implanted in a monkey (M. sinicus) and recovered therefrom in pure culture. There are therefore good reasons for concluding that the development were described is not abnormal, and that it is probably closely parallel to that which occurs naturally inside man.

In 1916, the writer (Van Cleave, 1916) called attention to the fact that lack of published records should not be taken as an indication of scarcity of Acanthocephalans in the Chinese fauna. A single species of Centrorhynchus has been described from a magpie, and Faust (1921 a) has recorded the species common in the hog. As yet, apart from these two specific identifications, the acanthocephalan fauna of China has remained unknown.

The European earwig (Forficula auricularia L.) accidentally introduced some years ago into the United States, is now abundant in several of the Western and at least one of the Eastern States; it has become established also in New Zealand, where, according to Tillyard, it has become a major pest, eating into peaches, nectarines, and apricots and rendering them useless for sale.

Twelve larval trematodes, herein described as Agamodistomum la-ruei n.sp., were found by Prof. La Rue, at the autopsy of a racoon, Procyon lotor lotor (Linn.), which had been kept for several months in captivity near Douglas Lake, Cheboygan County, Michigan, during the spring and summer of 1925. The parasites were found by teasing the lungs apart in water. It was not determined whether they were in the alveoli of the lungs or in the tissue. They were apparently not encysted.

The swallow bug, Oeciacus vicarius Horvath, is of common occurrence in North America, chiefly, if not entirely, upon the cliff swallows, Petrochelidon lunifrons (Say); it has been recorded from the barn swallow, probably in error.

It appears to be really distinct from the European swallow bug, Oeciacus hirundinis (Linnacus).

The habits, structure, and specific characters of the bug do not seem to have been adequately studied hitherto.

This paper deals with the external structure of the bug and of such of its biology as could be worked out under the handicap that its natural host could not be kept in captivity.

The bugs attack man readily, but do not appear to adapt themselves readily to living upon man or in his dwellings.

In 1916 Dr J. C. Becker made the interesting discovery of Bilharzia infection in Physopsis africana collected at Nijlstroom in the Transvaal and obtained the adult flukes in some guinea-pigs he had exposed to infection with the cercariae. The town of Nijlstroom is situated at the source of a tributary of the Limpopo river at an altitude of 3924 feet above the Indian Ocean into which it flows. In 1917 I collected2 infested examples of P. africana at Magaliesburg, a popular picnic place for Krugersdorp residents, situated on a branch of the Little Crocodile river which later joins the Limpopo. Magaliesburg has an altitude of 5000 feet above sea-level. I also obtained infested examples from Rustenburg, thus revealing a further source of infection from tributaries of the Little Crocodile river, at an altitude of over 4000 feet.

1. A Heteromita species, probably Heteromita globosa, is described and the methods of culture and observation are detailed.

Heteromita globosa is a flagellate with a karyosome nucleus. The karyosome body is an achromatic structure. The chromatin lies on or around the periphery of the karyosome as a narrow diffuse layer and is also distributed upon the inner side of the nuclear membrane. There are two unequal flagella which arise from two blepharoplasts which are situated close together at the anterior end of the body. The blepharoplasts are connected with the nuclear membrane by fine rhizoplasts.

2. The division, encystation and excystation of the flagellates are described from living and stained material. The nuclear division is characterised by a well-developed spindle and the chromatin is arranged in an equatorial plate at the metaphase. The blepharoplasts play the part of centrosomes in the division of the nucleus.

3. The normal division in the living state takes 7 to 15 minutes. The blepharoplasts can be seen to separate, the nuclear space becomes hyaline and ceases to refract in the characteristic way, the space elongates, the blepharoplasts each with the flagellum attached come to lie at opposite poles of the elongating organism and a second flagellar rudiment can be seen to arise at each end alongside of the original one. The nuclei can be observed to reconstruct and the protoplasmic body draws apart rapidly, leaving a narrow protoplasmic junction which breaks through and the two daughter individuals separate.

4. A process of delayed division was observed. If after the division of the nucleus and the drawing apart of the main bulk of the protoplasm the actual breaking of the narrow junction between the two daughters fails to take place immediately, there seems to be no means of effecting this actual separation until the occurrence of a new nuclear division.

In the course of a few hours, usually 3 to 6, a second division occurs and each nucleus undergoes mitosis and the creature splits into four daughters.

The double individuals may encyst and when they emerge they do so as a single binucleate protozoan equipped with a double flagellar apparatus.

5. Syngamy has not been observed.

This species has received so few notices from collectors of parasitic Copepoda that it might be judged uncommon. Thus Krøyer (1837), originally placed it in the genus Lernaeopoda having but a single specimen at his disposal the host of which he had forgotten; subsequently it has been recorded by Olsson (1869), who was the first to place it correctly in the genus Brachiella. This species has also been recorded by P. J. van Beneden (1870), by T. Scott (1901), by A. Scott (1904), and collected by L. Harrison Matthews, as mentioned by me (1926), at Plymouth.

During the summer of 1927 Mr W. J. Hamilton, a student in the Department of Entomology, Cornell University, collected biological material in parts of Cuba, Panama, and Costa Rica. He brought two small vials of parasites taken from bats. Though the collection contained only 24 specimens yet it is of interest on account of the rarity of some of the species. It is, therefore, thought worth while to offer the following brief notes on the species taken.

The investigation deals in detail with the structure of the immovable and movable parts of the head of the Nycteribiidae. The muscles of the head are also studied.

The head capsule is modified from that of the Hippoboscidae. The vertex is not subdivided into several anatomically differing subregions. The occiput is represented by the border of the occipital foramen only. The postgenae are separated by the median membranous region of the head, as in the Hippoboscidae. The ptilinum serves as a flexible joint connecting the fronto-clypeus with the vertex and the genae. The fronto-clypeus is much more modified than that of the Hippoboscidae and is movable. The eyes are reduced to one or two facets, or are entirely absent. The greatly modified ocular sclerites are present in Cyclopodia only.

The antennae consist of the pedicle and the flagellum, the latter being concealed in the cavity of the former. They have the same structure as those of the Hippoboscidae parasitising birds.

The proboscis has much in common with that of the Hippoboscidae though it differs greatly in detail. It is composed of the rostrum, the haustellum and the labella.

The rostrum belongs morphologically to the head and is formed of the same parts as in the Hippoboscidae. All the parts of the rostrum, with the exception of the tormae, have the same arrangement as in that family. The tormae are separate and are attached at the lateral borders of the fronto-clypeus.

The haustellum is composed of the theca, the labial gutter, the labrumepipharynx and the hypopharynx. The two former parts belong morphologically to the labium, but differ in detail from those of the Hippoboscidae. The very short labrum-epipharynx is enclosed in the posterior part of the labial gutter.

The hypopharynx is very slender and as long as the theca; it is enclosed in the cavity formed by the dorso-lateral parts of the labial gutter.

Labial glands are present in the bulbous part of the theca; their ducts open into the food canal. All the muscles of the bulbous part of the haustellum are homologous with those of the same part of the proboscis of the Hippoboscidae.

The labella are entirely membranous, are armed with two inner and six prestomal teeth and their surfaces have serrated ridges. There are six gustatory sensillae on the membrane of each labellum, which are connected by the intralabial canaliculi with the sense cells of the bulbous part of the theca.

The cutting action of the teeth of the labella depends upon the protractions and retractions of the narrow part of the theca. When this part retracts it everts the inner membranous walls of the labella, and the teeth, being attached to these walls, perform protrusible divergent movements.

The present paper is the fifth instalment of the Report on the Molteno Institute collection, of which Parts I–III (Ascaeidae, Heterakidae, Oxyuridae, Camallanidae, etc.) and Part IV (Trichostrongylidae and Strongylidae) were published in this Journal by Dr H. A. Baylis (1923) and myself (1926). This collection was sent to Cambridge by Dr E. Hindle and consisted chiefly of unnamed material which had accumulated in the Parasitological Laboratory of the Egyptian Government School of Medicine in Cairo. Since commencing the work on the Filarioidea contained in this material, a further series of worms belonging to this order was placed at my disposal by the Cairo Medical School and the results of my study of this collection have been incorporated with those of the Molteno Institute specimens.

In July, 1927, Dr Kenneth Smith took a specimen of the Hippoboscid fly Ornithomyia avicularia on the window of a building at the Cambridge University farm. The fly was lethargic and easily captured, and, noticing that its abdomen was infested by some parasite, the captor kindly handed me the specimen.

During the eighteen months spent with the League of Nations International Commission on Human Trypanosomiasis, I had a unique opportunity for studying the transmissibility of the human trypanosomes by Glossina palpalis.

The two genera here considered agree with one another and differ from all the other members of the Lernaeopodidae in having the abdominal appendages dorsal to the eggstrings; and all their species so far described are parasitic upon some species of ray.

Parasitology, 20, 87. The legend to Fig. 7 should read: A 1. = antennules; A 2. = antennae.

Generic Diagnosis, ♀. Cephalothorax with transverse lateral expansions, small in young, resembling a hammer in old specimens, between whose anterior surfaces projects the head. Neck smooth, cylindrical and without swimming feet. Trunk much enlarged transversely, smooth, flattened dorsiventrally, bearing a pair of posterior appendages profusely and dichotomously branched. Abdominal appendages reduced to two small knobs; or one undivided abdomen.Egg-strings long and straight; eggs multiseriate. Two pairs of antennae, twopairs of maxillae, one pair of maxillipedes.

During the early part of 1928, a census of the rookeries in the Oxford district was carried out by the Oxford Bird Census organised by Mr E. M. Nicholson. This work raised a number of problems, of which one of the most important was that of natural checks to the numbers of rooks. Although shooting of the young rooks is one of the greatest checks on their population, Mr Nicholson's observations showed that there must also be a mortality amongst the nestlings. Lewis (1925, 1926 b) has shown that gape-worms are common in starlings (Sturnus vulgaris), and it seemed possible to us that this parasite might also be sufficiently common in rooks to cause deaths among the young birds. The gape-worm had already been recorded from the rook by Lewis (1926 a) and Baylis (1928), so that the possibility seemed well worth investigating.

Owing to the kindness of Dr H. A. Baylis I have recently had the opportunity of examining portions of two species of Avitellmine tapeworms, both of which are new to Helminthology and both of which belong to a genus which is distinct from the two genera which have hitherto represented the Avitellininae. The material which I have examined is the property of and is deposited in the British Museum (Natural History) at South Kensington, London.