Under the name of Zografia notonectae n.g., n.sp., Bogoyavlensky (1922) has described a new organism which he found parasitic in the body cavity of Notonecta (Hemiptera) collected in ponds in Russia (government of Moscow).

The insect fauna of tree wounds with sap-exudations or “slime flux,” as well as that of the water-filled hollows of trees, has already attracted the attention of entomologists and several interesting life histories of insects have been recorded from these media. In the present paper I propose to deal with the fauna of only one tree, a horse-chestnut standing on the Downing site between the School of Biochemistry and the Molteno Institute. For several years this tree has supplied me with very rich material for the study of Dipterous larvae and their parasites. Unfortunately, this study recently came to a natural end when this tree, with several others, was cut down to make place for a new building. This fact justifies the publication of the present records of observations collected during several years, although I do not consider them as complete. The most interesting feature of our horse-chestnut tree was the presence of two kinds of lesions each harbouring a different fauna: (A) a sap-exudating or “ slime flux ” wound, and (B) a waterfilled hollow or reservoir.

1. T. raiae and Bodo caudatus are investigated using Feulgen's nucleal reaction in addition to the usual nuclear stains. The nature and value of this method is discussed.

2. In T. raiae the parabasal body or kinetonucleus is found to consist of chromatin as shown by the nucleal reaction. An achromatic element in its composition is suggested in the division by the desmose between the two halves being achromatic.

The blepharoplast is an achromatic structure. It seems probable that it persists in the aflagellar phase of the trypanosome. In T. raiae the division of the blepharoplast precedes but does not apparently orientate the division of the parabasal body. The division of the parabasal body does not present a mitotic figure.

3. The nucleus in T. raiae consists of an achromatic karyosome body with some chromatin surrounding it, there is also chromatin arranged upon the inner surface of the nuclear membrane.

4. At division the karyosome apparently draws out into an achromatic spindle figure, the chromatin collects in the prophase into a loose granular mass and then becomes arranged at the equator. The mass divides into two portions; it is not possible to distinguish chromosomes with sufficient certainty. The nuclei are finally reconstructed from the achromatic ends of the spindle and the chromatin which has travelled to either pole.

5. In Bodo caudatus the parabasal body (kinetonucleus) is composed of chromatin and of an achromatic substance, the blepharoplasts or basal granules are achromatic bodies which play an orientating part in the division of the parabasal body: this division does not show an equatorial plate stage. The nucleus is made up of an achromatic nucleolus-karyosome surrounded by a hollow sphere of chromatin; there is a very definite division process which takes place apparently within the nuclear space. There is no equatorial plate formed and the achromatic figure which is derived directly from the karyosome is a division column which inserts itself into the already dividing chromatin and is not of the spindle fibre type found in the mitosis of the metazoan cell and of many protozoa.

The host of the Coccidian described in this paper is Hydroporus palustris L., a small Dytiscid beetle common in stagnant ditches. The infected material was collected from two ditches in the neighbourhood of Grantchester (Cambridge). From one ditch 25 per cent. of the beetles were parasitised, and from the other ditch 15 per cent. were parasitised. The infection with Legerella, which is confined to the malpighian tubules, is often very intense. Heavily infected beetles are readily recognised on dissection because the malpighian tubules are colourless and do not contain the brown excretory granules characteristic of the normal tubules. The parasite has been observed at all seasons of the year, and the life cycle does not appear to follow a seasonal course.

In his experiments upon the toxicity of oxygen for protozoa Cleveland (1925, a, b, c) was able to kill the intestinal protozoa of Termites, without injuring the host, by increasing the pressure of oxygen for varying lengths of time. He found that at one atmosphere pressure of oxygen the intestinal protozoa of Leucotermes were killed in 24 hours; those of Termopsis in 72 hours; whilst those of Reticulitermes and Cryptotermes were not all killed in ten days. At 3·5 atmospheres of oxygen he found that the intestinal protozoa of all four species were killed in less than an hour. At this pressure the intestinal protozoa of cockroach and frog were killed in 3½ hours and 28 hours respectively, whereas it took 90 hours to kill the cockroaches and 65 hours to kill some of the frogs. He also experimented upon warm-blooded vertebrates (rats), but he found that these animals survived only 5–6 hours at 3·5 atmospheres of oxygen and their intestinal protozoa were not killed in that time. Trichomonas, grown in cultures, however, from frog, rat, and man, were killed in 6, 10, and 11 hours respectively when subjected to 3·5 atmospheres of oxygen.

Adult. Eyeless; camerostome without movable cheeks. In size (largest specimen 14 × 9 mm., Smallest 9 × 6 mm.), configuration, grooves, etc strongly recalling O. coriaceus, and the younger specimens have a suggestion of a similar dorsal pattern, but the whole surface is uniformly mammillate and the hood and the rather long palps are visible from the dorsal aspect. Discs in most specimens inconspicuous. Basis capituli about as broad as long, broadest posteriorly, where there are short, stiff, caducent bristles (? three pairs) directed outwardly. Hypostome lanceolate, with very small corona, followed by 2/2 well spaced teeth, about 6 per row. The leg armature, best understood from Text-fig. 1, is highly characteristic, the most striking feature being a prominent, rather sharp tooth on the proximal false articulation of the tarsus in legs I, II and III, but absent on tarsus IV. All the tarsi bear a prominent dorsal tooth near their distal ends. Legs I and II show characteristic prominences on other articles, notably the penultimate, which has a dorsal tooth at its basal and distal extremities.

Balantidium coli (from the domestic pig) can be readily cultivated in the medium devised by Dobell and Laidlaw (1926) for the cultivation of entozoic amoebae (inspissated horse-serum and Ringer-eggwhite, with solid rice-starch). If the hydrogen-ion concentration does not exceed the limits p H = 5·4–8·0, rich cultures can be obtained in this medium, at 37° C.; and strains of the ciliate can be readily propagated for any desired period if subcultures are made every 3–5 days.

In such cultures conjugation occurs periodically; but encystation has never been observed, and all attempts to induce it under cultural conditions have hitherto failed.

The conjugation of Balantidium, as seen in cultures, is peculiar, but it has been impossible as yet to elucidate all details of the process. Conjugants are always much smaller than non-conjugants, and frequently unequal in size. Apparently but one conjugant is fertilised, and survives as an exconjugant—the partner dying after separation.

Encystation has never been seen to follow conjugation, as described by Brumpt (1909).

In cestodes of this family, the number, size, and shape of the rostellar hooks is needed for the identification of the species. While number and size are often quoted (e.g. Fuhrmann, 1924 a) the shape is usually ignored owing to the impossibility of reproducing innumerable figures: this greatly lessens the usefulness of such lists as the one above mentioned, especially to workers not in touch with a well-stocked library. For this reason the formula illustrated in Text-fig. 1 is suggested. The base, AB, of the hook is considered as unity and other measurements are expressed in decimals of it. EH is a tangent drawn parallel to AB and touching the hook at its highest point H; GB, FC and KL are perpendiculars drawn from AB to the two extremities G, F of the hook and to the inside, K, of the curve FG. With the points A, G, H and K fixed the approximate shape of the hook is determined: the various formulae may then be compared or the hook itself be reconstructed. Text-fig. 2 gives examples of the various types of hooks and their respective formulae, Text-fig. 3 of their reconstruction from the formulae. This arrangement appears preferable to that of Stevenson (1904) as being simpler and also facilitating reconstruction.

The rich material of Ixodoidea in our Museum, which I have recently studied, enables me to give records of the geographical distribution of some genera. The genus Dermacentor of the vast Russian territory, as I have shown elsewhere, is represented by two widely distributed species, D. reticulatus and D. niveus. The collection contains specimens from the following localities.

Linnaeus (1747) described and figured (reproduced in Fig. 1) a parasitic Copepod from the gills of a Gadus, which he designated Lernaea cauda duplici tereti, and defined in these words: Thorax seu corpus molle, album, subrotundum, convexum, carnosum; antice obtusum, seu potius retusum, latere utroque notatum, denticulo molle antrorsum spectante. Collum tenue longiusculum, caput trilobum dilatatum; lobo intermedio obverse eordato. Cauda pone thoracem ex duobus corpusoulis pallidis longitudine thoracis. Brachia sub thorace, ad latera colli utrinque duo, quorum pars exterius bilobum, interius ovatum.