In view of the morphological similarity of T. evansi and T. brucei, including the sporadic occurrence of marked polymorphism in the first-named species, the hypothesis is advanced that T. evansi may have originated from T. brucei, by the introduction of the last-named species into localities free of Glossina and its subsequent propagation by direct passages.

The possibility of contact between the mammalian host of T. evansi, on the one hand, and Glossina and tsetse-borne trypanosomiases, on the other, is shown to exist in the Anglo-Egyptian Sudan, thus pointing to the source from which T. evansi in that country may have originated and providing circumstantial evidence in support of the hypothesis.

Attempts were made to discover whether T. evansi is capable of developing in Glossina. A total of 568 flies were fed on infected mice and examined at periods from 6 hr. to a fortnight following the infective feed. The results were entirely negative: not only is the trypanosome incapable of establishing an infection in the fly, but the majority of flagellates perish and are digested during the first hours after ingestion by the insect.

The behaviour of T. evansi in tsetse is shown to be similar to that of non-transmissible strains of trypanosomes of the Brucei group after prolonged maintenance by direct passages in the mammalian hosts, and is therefore also in keeping with the hypothesis.

There are about seven species of the genus Ascodipteron in the tropical parts of the Old World. Their endoparasitic females, which live embedded in the skin of bats, are not uncommon on certain species of the genera Emballonura, Hipposideros and especially of Rhinolophus and Miniopterus. The males, on the other hand, are extremely rare, and have never been taken on bats before. There is a description of the male of Ascodipteron speiserianum only, by Muir (1912), who bred this species in Amboina, Dutch East Indies.

1. The feeding of the tick Ixodes ricinus was studied in relation to the reproductive condition of the host, in this case the hedgehog Erinaceus europaeus.

2. Hedgehogs in hibernation, in full breeding condition, and injected with male and female sex hormones, were parasitized with unfed nymphs and female ticks in midwinter.

3. Attachment and engorgement of the ticks was successfully accomplished on both sexually active and inactive hosts. The longer time required to complete engorgement on the hibernating hedgehogs may be explained by their lower blood temperature.

4. Parasitization by this tick does not appear to be related to the reproductive condition of the host animal, and the amount of sex hormone in the host's blood has no apparent immediate effect on the fecundity of the tick.

The genus Microcotyle of the order Monogenea is a large one, containing about forty species, and it is well summarized by MacCallum (1913, 1915).

Experiments on the inactivation of various plant virus preparations by ultra-violet light and by X-rays are described. The curves obtained by plotting against the dose of radiation the number of lesions obtained on inoculation of a test plant are exponential and the rate of inactivation is proportional to the intensity of the radiation. The inactivation curves obtained with preparations of a given virus in different states of aggregation do not appear to be systematically different.

The discussion of these results shows that the particles in an aggregated virus suspension cannot be considered to be permanent clusters of elementary virus particles. Two possible alternatives which are compatible with the radiation experiments are discussed, either (a) the aggregation consists of the attachment of a single elementary virus particle to inert matter, or (b) the aggregation consists of a reversible union of elementary virus particles, there being a dynamic equilibrium between the aggregates which are constantly dissociating and the elementary particles which are constantly aggregating. The dose of X-radiation required for inactivation of the virus is consistent with the view that inactivation is caused by the production of a single ionization in the elementary virus particle, the size of which is approximately known from nitration experiments.

Very little appears to be known—at least by students of intestinal protozoa, and general parasitologists—about the man whose name now lies entombed in the familiar flagellate genus Lamblia. We all know, of course, the organism to which this name was given by Blanchard in 1888, and we are all aware that it was dedicated to a person called Lambl, who is popularly supposed to have discovered it. We all know also that Blanchard's genus had been forestalled by Kunstler's Giardia (1882), though many of us continue to use the first name in everyday speech; while some of our less cautious writers, even now, continue to ascribe to Lambl the discovery of the intestinal amoebae of man.

1. The morphology and life-history of Dientamoeba fragilis, as observable in cultures, are described and illustrated, and the stages correlated with those commonly found in human faeces.

2. The nuclear structure especially is reinterpreted, and nuclear and cytoplasmic division are described in detail.

3. It is shown that the “normal” binucleate condition of this “amoeba” represents an arrested telophase stage of mitosis—the “granules” in the nuclei being really chromosomes (constant in number), and the strand connecting the nuclei being a persistent centrodesmus. The chromosome number is probably 6 (certainly not 4).

4. Binary fission is the only method of reproduction hitherto observed: no cysts or other stages in the life-history have been discovered.

5. Attempts to transmit D. fragilis to a man and 2 macaques (M. rhesus and M. sinicus) by administration of trophic amoebae per os—and in the case of M. rhesus inoculation per anum—were unsuccessful. It was also found impossible to infect chickens permanently by injection per anum (though one chick acquired an infection lasting for a week).

6. Consideration of its cytology and development leads to the conclusion that D. fragilis is not a true amoeba but an aberrant flagellate closely related to Histomonas. No flagellate stages, however, have yet been discovered.

7. Some consequences of this conclusion are briefly discussed, and hopeful directions for further inquiries are indicated.

8. On analogy with Histomonas, it is suggested that D. fragilis may be conveyed from man to man not by direct oral infection with trophic forms but in the ova of a nematode worm—possibly Trichuris (or Ascaris?).

An account is given of ultrafiltration studies with Nicotiana virus 11 (tobacco necrosis virus). It is shown that though the filtration end-point is about 40 mμ, there is invariably a sharp drop in the local lesion counts between the membrane pore sizes 250 and 125 mμ. This phenomenon shows itself as a “bench” or shelf with an upward trend in the filtration curve (see Text-fig. 1, curve A). A number of possible explanations are given. The fact that increasing dilution raises the height of the bench leads to the deduction that large particles are breaking up into smaller ones, the larger particles being aggregates of the smaller. Experiments on resuspension of virus inside the filter and fractional filtration support the same conclusion.

From the filtration end-point the particle size of the virus is computed to be between 13 and 20 mμ.

Seven species of marine fishes and three of fresh or brackish water Canadian fishes have yielded new or known Myxosporidia. The marine fishes were from St Andrews, New Brunswick and Halifax, Nova Scotia, places 250–275 miles apart by sea, and from the Labrador coast. The brackish and freshwater fishes were obtained in Montreal and the Salmon River, Nova Scotia.

Descriptions and illustrations are given of the morphology of five new species of Myxosporidia: Ceratomyxa urophysis, Myxoproteus myoxocephali, Myxidium myoxocephali, Myxosoma diaphana and Henneguya amiae.

Chloromyxum leydigi Mingazzini, C. granulosum Davis, Myxidium lieberkuhni Bütschli, Myxidium gadi Georgévitch and Zschokkella hildae Auerbach are recorded from new piscine hosts in Canada.

Some effects of the Myxosporidian infections, both macroscopic and microscopic, on their hosts are considered. Comparison of the effects of similar infections of Myxosporidia on allied fishes in Normandy and Eastern Canada has shown a general similarity between them.

The economic importance of some Myxosporidian infections of the edible fish examined is shown by parasitism of the cod, haddock and sculpin. Amia calva is also used for food in Montreal. The possibility of edible fishes acquiring Myxosporidian infections by way of their food is noted, with reference to the host-specificity of the Myxosporidia of Fundulus heteroclitus described by Bond.

The influence of environment on and powers of adaptation to different habitats exhibited by certain Myxosporidia is discussed.

Some remarks are made on the zoogeographical distribution of certain Myxosporidia and their piscine hosts.

Mycetosporidium jacksonae n.sp. occurs as a parasite in the intestinal epithelium and the malpighian tubules of weevils of the genus Sitona. The life history comprises vacuolated and compact plasmodia in which arise ovoid or spherical multinucleate bodies resembling coccidian schizonts. Sporulation results in the formation, within thin-walled sporangia, of 8-nucleate, biconvex spores with densely staining, resistant walls. Other types of multiplication occur in the form of small uninucleate, fusiform bodies developed directly from the plasmodia; and of small uninucleate, ovoid or fusiform bodies, four to six of which are formed within each chamber of a multilocular sporangium.

The parasite resembles M. talpa Léger & Hesse 1905, but differs in some characters and, consequently, the new species M. jacksonae is made for it.

The genus Mycetosporidium is of uncertain systematic position and appears to be related to the Mycetozoa, but it also resembles the Haplosporidia in some characters.

(The slides upon which the description of M. jacksonae is based are deposited in the Molteno Institute of Biology and Parasitology, University of Cambridge.)