The biotic factors in the environment of the tick, Ixodes ricinus, exercise little effect on the geographical or local distribution of the species, or on its seasonal prevalence.

The local distribution is determined by edaphic factors, a wet, mossy, or peat soil and a dense mat of old vegetation or a rank growth being necessary for survival of the tick. In Britain, the critical season for survival is summer, during which the moisture factor in the microclimate acts in a limiting capacity.

The seasonal prevalence is determined by temperature. Within limits, which appear to correspond to air-temperature limits of 7 and 16° C. (weekly maxima), the unfed tick climbs the vegetation, and thus readily obtains a host. In Britain, it is inactivated in winter by the cold, and in summer it is less readily picked up by hosts because of its positive geotropic response to the stimulus of high temperatures.

The summer is, in Britain, the optimum season for development, which also proceeds to some extent in winter. Autumn and spring are parasitisation seasons. The life cycle, involving a parasitisation and a development season for each stage, requires a minimum of 1½ years. The period may extend to 4½ years.

The possible world distribution of the species is limited primarily by temperature. Thus, microclimatic extremes of — 14 and 35° C. limit the range through which the tick can survive. A period of at least 3 months with the mean air temperatures over 10° C. is necessary for development, while the mean air temperature of the coldest month must not exceed 10° C. to allow of parasitisation occurring.

Within the areas delimited in relation to the temperature requirements of the tick, distribution is governed by the moisture factor. An index of the suitability of an area within the temperature limits is afforded by the type of vegetation; forest and woodland, including grass and cultivation areas, as opposed to prairie and steppe, indicate suitable moisture conditions.

(1) Female Ixodes ricinus ticks which feed on a sheep infected with tick-borne fever are not capable of transmitting the infective agent to their progeny. Only the nymphs and females, therefore, can be infective to sheep. In the case of an infective female, the infection may have been acquired, (a) in the immediately preceding stage, or (b) in the larval stage, the infective agent remaining in the tissues of the tick during the nymphal engorgement and subsequent moult. This appears to occur irrespective of whether the host on which the nymph feeds is a susceptible or an insusceptible. animal.

(2) Ticks which have acquired infection are infective as soon after moulting to the next stage as they are able to attach to hosts. Unfed ticks were not found to be infective after a period of about 14 months.

(3) Infection is transmitted to the sheep in the course of the 2nd day after attachment of infective nymphs.

(4) The disease may be transmitted to sheep by inoculation of emulsions of infective ticks, if these have been allowed to commence engorgement. The use of saline for such emulsions appears to be inadvisable.

There is still some difference of opinion as to the classification of what Rudolphi in 1801 called the Amphistomata. Fischoeder (1901—4) regarded all “Amphistomes” as belonging to a single family, the Paramphistomidae. Stiles & Goldberger (1910) proposed the elevation of the group to the status of a superfamily, the Paramphistomoidea, comprising three families, Paramphistomidae, Gastrothylacidae and Gastrodiscidae. Braun (1911), Odhner (1911), Looss (1912) and Stunkard (1925) have maintained Fischoeder's view; Maplestone (1923) and Travassos (1934) have preferred that of Stiles and Goldberger.

In a very important revision of the Streblidae, Speiser (1900) classified them into two subfamilies: (1) the Nycteriboscinae and (2) the Streblinae. To the first subfamily he referred all the genera of the world, with the exception of Strebla and Euctenodes. Upon the presence of the ctenidium and some other characters these two American genera were included in the second subfamily. This classification of the subfamilies was also adopted by Kessel (1924, 1925).

The main theme of this series of papers will be the power of the three wellknown members of the brucei group of trypanosomes, T. brucei, T. rhodesiense and T. gambiense, to infect man. Inextricably involved with this problem are two others, both of practical importance: (1) Can the African big game serve as a reservoir for human trypanosomiasis? and (2) What are the affinities existing among these three trypanosomes? This may appear to be an inversion of the real order of importance, but a study of the literature on the brucei group, past and recent, reveals that infectivity to man dominates all other considerations.

In this section are collected all the instances recorded at this laboratory of the testing of T. gambiense on man, after the trypanosome had been maintained for a time in laboratory animals.

Of the five species of helminths of the British muskrat (Ondatra zibethica L.), two (Notocotylus quinqueserialis and Hymenolepis evaginata) have been introduced with the animal. The three other species of helminths (Capillaria hepatica, Taenia taeniaeformis larva and T. tenuicollis larva) have probably been largely re-acquired from the local fauna. All of the three common species of ectoparasites [Laelaps multispinosus (Tetragonyssus spiniger), Listrophorus validus and Dermacarus n.sp.] occur in North America. Three other species (Tyroglyphus sp., Myobia n.sp., Polyplax sp.) have occurred as single individuals, the last species having probably been acquired from the water vole. Introduction into Britain has greatly depleted the original helminth fauna as regards number of species and individuals; but not so with the ectoparasites. Lists of the parasites hitherto recorded from the muskrat are given and those found in brown rats (Rattus norvegicus Erx.) and water voles (Arvicola amphibius amphibius L.).

1. Experiments upon Xenopsylla cheopis Roths. are described which were carried out to discover if feeding influenced duration of life or had any effect upon the survival of the sexes or upon the relationship between duration of life and saturation deficiency of the atmosphere.

2. Fleas fed once before starvation lived longer than unfed fleas. There was no difference between survival of the sexes and no direct proportion between survival times and saturation deficiency.

3. Fleas kept with the host for 7 days before starvation lived still longer. Females lived considerably longer than males, but there was still no direct proportion between survival times and saturation deficiency.

The following animals are from a collection made for and kindly presented to me by Miss Miriam Rothschild during her visit to Brighton in July and August 1935.

1. A detailed description is given of a coccidian which parasitises the nuclei of the intestinal cells of the polychaete worm Polydora flava Claparède. The final stages in sporogony have not been observed; nevertheless, this is the first record, from an annelid worm, of an eimeriid which shows a striking resemblance to those Coccidia occurring in the higher animals. It is also the first record of an intranuclear parasite from an annelid.

2. From the gut of the same worm, a new species of Selenidium is described. It differs from all other species, hitherto recorded, in the possession of an axial tube, which completely encloses the nucleus and extends from one end of the organism to the other: hence it is proposed to name this organism Selenidium axiferens. The anterior end of the trophozoite shows a circlet of siderophilous bodies, which Ray (1930 a) has shown to be characteristic of the genus.

3. Both uninucleate and multinucleate intracellular forms, with polar groups of chromatic globules, have been discovered in great abundance on six occasions; no merozoites have been found, but evidence is submitted to show that these intracellular forms represent the schizogonic phase in the life-cycle of the Selenidium.

4. Sporogony follows closely that described for other species, but the final stages have not been observed. The gametocysts measure 48 × 50–70 × 63μ.

5. Association and cyst formation are described in Polyrhabdina polydorae Caul. & Mesn. (?) for the first time. Innumerable nuclei make their appearance in each gametocyte, before ejection of the cysts into the sea-water takes place. Gametocysts can easily be distinguished from those of Selenidium axiferens, not only by their morphology, but also by their greater size (98 × 90–105 × 100μ).

The comparative resistance to high temperature and various humidities of four species of blow-flies, Calliphora erythrocephala Meig., Lucilia sericata Meig., Sarcophaga falculata Pand. and Phormia groenlandica Zett. is studied. It is shown that Phormia groenlandica is the most resistant species and Calliphora erythrocephala the least resistant species, with Lucilia sericata and Sarcophaga falculata occypying an intermediate position.

This order of resistance is correlated negatively with the order of the seasonal succession of the species.

It is suggested that certain differences in the length of life of males and females subjected to various humidities is brought about by an “ageing” factor.

The nematode described here was collected by the Wyoming field party of the United States Bureau of Fisheries during the summer of 1934. The Rocky Mountain whitefish, the Eastern Brook trout, and the rainbow trout serve as hosts for the parasite. In several instances pathological changes, particularly of the gonads, were found to accompany its presence.

In July, 1934, I found a trichomonad-like organism in water taken from a pond in Lincolnshire. Its morphology, and method of division, and also the cultural conditions under which it will grow, have been described previously (Bishop, 1935). It was named, provisionally, “Trichomonas” keilini. In “T.” keilini, unlike most trichomonads, the undulating membrane is short, the bordering flagellum never becomes free, and there is no basal fibre beneath the undulating membrane. “T.” keilini was never found directly in the pond water but only after it was centrifuged and allowed to stand for 7–21 days.

Specimens collected by the Swedish Expedition to the White Nile in 1901 have been identified as Rhadinorhynchus niloticus Meyer, 1932. On the basis of this material, including the first recorded females, the species has been restudied. Points wherein the individuals are unlike the forms included in the family Rhadinorhynchidae are presented in detail. A new genus, Tenuisentis, is proposed with Rhadinorhynchus niloticus as type. This new genus becomes type of a new family, the Tenuisentidae, which is assigned to the order Eoacanthocephala.