Numerous specimens of this fluke were obtained on several occasions from domestic ruminants which were examined at Mukteswar. It has been ascertained that the infection occurs very commonly among goats and sheep, and occasionally also among bulls. Two buffaloes were also examined for infection with these flukes, but with negative results. The intensity of infection, particularly among ovines, is very great, several hundred specimens being obtained every time. Although these worms are found in all parts of the alimentary canal posterior to the oesophagus, the usual seat of predilection is the small intestine. On one occasion only were a few worms found in the bile ducts. It has been observed that the flukes die soon after the death of the host and begin to undergo post-mortem changes. For this reason it was often found difficult to obtain satisfactorily stained preparations of the parasites. Usually acid haematoxylin gave better results than the various carmine stains. The following description of the worms is based on the observation of several unstained and stained preparations and eight series of sections made through various planes.

Through the courtesy of Prof. Ali Akhtar, Afghanistan, the writer examined about eight flukes obtained from the trachea of the spoon-bill, Platalea leucorodia var. major. A short account is given of the species, and its affinities are discussed below.

1. Aphidius matricariae Hal. is an internal parasite of Myzus persicae Sulz.; it was also found parasitizing M. circumflexus Buckt. and Aulacorthum solani Kalt. (Myzus pseudosolani Theob.).

2. The percentage of aphides successfully parasitized increased with an increased number of strikes per host. A single female can lay up to 350 eggs, and one female successfully parasitized 309 M. persicae.

3. The female parasite reaches its maximum activity during the 2nd or 3rd day of oviposition, and this activity has no correlation with light intensity.

4. The disappearance of supernumerary larvae due to cannibalism has been observed.

5. The species is arrhenotokous. Mating takes place from 2 hr. after emergence. In the progeny of early matings the females preponderated; in later matings the sex ratio was approximately 1:1.

6. The parasite appears to fly under the same conditions as those generally favourable for aphides. It is generally disseminated by flight of the adult itself and through localized movements of parasitized apterous aphides.

7. The host is unable to reproduce if ‘struck’ in the 3rd instar or earlier.

Among a very large number of preparations reputed to possess mosquito-repellent properties, only a few are really efficacious. The most commonly used preparations are those prepared with citronella oil. Definite information, however, on the comparative efficiency of many of these preparations is lacking. It was therefore our object to determine the value of different culicifuges under laboratory conditions. The experimental results obtained in this connexion are sufficiently promising to justify their publication, especially because owing to the war the want of an effective and a cheap culicifuge is all the more important.

1. The carcasses of 154 silver foxes of various ages, from fifteen farms in the southwest, have been examined and their parasites recorded. In addition, those of fourteen wild red foxes have similarly been examined.

2. The incidence of various species of nematode, cestode, and protozoan parasites has been analysed for the foxes, in age groups and in farm groups.

3. The worm egg counts in the faeces have been discussed in relation to the numbers of female worms in the foxes. No adequate correlation has been established between the two sets of data.

4. The ages of the foxes at incidence of the nematode parasites has been discussed, and the possibility of the development of resistance to various species investigated.

5. Certain peculiarities in the sex ratios of the Nematoda have been discussed.

6. The possibility of infestation of silver foxes by parasites derived from the wild-red-fox population of the neighbourhood of the farms has been investigated, as has also that of the transference of Crenosoma striatum from the hedgehog to foxes.

The louse populations of the heads of 93 infested children, 45 boys and 48 girls under 14 years of age from a northern English industrial city have been examined.

The average number of lice per head was 14·8 for all children, 12·7 for boys and 16·8 for girls. The maximum population observed was 142.

The majority of infestations (65%) were light with under 10 lice. Girls were more frequently heavily infested than boys.

Most of the infestations, though light, must have been established at least for some weeks.

In this paper two new genera of Laelaptidae are raised, the first for four large mites taken oh a banded mongoose, the second to fit a number of females taken on a squirrel. In addition to these new genera, two new species of Liponyssus and a new species of Haemolaelaps are described. All these specimens have been collected in Uganda.

The spermatophore in Ornithodorus moubata consists of a bulb with a neck at the end of which are two large capsules. When the spermatophore issues from the male opening the capsules are invaginated into the bulb to form a compact but tense object which the male applies to the female aperture with his proboscis. The male releases his grip on the neck, and the tension in the walls of the bulb causes the capsules to evaginate and thus enter the uterus of the female.

Some new species of Mastigophora and Sporozoa and a Microfilaria, parasitic in fish, frogs and toads in eastern Canada, are described and illustrated.

Trypanosoma percae n.var. canadensis from the yellow perch, Perca flavescens, is monomorphic, smaller, with a shorter, broader body and shorter free flagellum than Trypanosoma percae from European Perca fluviatilis. Trypanosoma myoxocephali n.sp. from the longhorn sculpin, Myoxocephalus octodecimspinosus, is small, with a narrow undulating membrane. It is the first trypanosome to be recorded from Myoxocephalus. Trypanosoma lavalia n.sp. from Bufo americanus is delicate, with a prominent undulating membrane with two myonemes. Trypanosoma gaumontis n.sp. from Bufo americanus is small, crook-like, with undulating membrane with deep folds and one myoneme very-near the bordering flagellum. There is no free flagellum. Trypanosoma montrealis n.sp. from Bufo americanus is long and sinuous, with very short free flagellum and without chromatoid granules in the cytoplasm.

Trypanosoma rotatorium (Mayer) is described from Rana catesbiana from eight sites, R. clamitans from three sites, and R. pipiens from three sites in Quebec Province. Trypanosoma inopinatum Ed. & Et. Sergent is recorded from Rana catesbiana and R. pipiens, A form similar in dimensions and morphology except for a much shorter free flagellum has been found in R. catesbiana from St Eustache.

Spirochaeta manitoui n.sp. is described from the blood of Rana catesbiana from Lake Manitou.

Lankesterella canadensis n.sp. from Rana catesbiana from Montreal and Lake Manitou is described and illustrated. Intracorpuscular forms have polar vacuoles, schizogony occurs in endothelial cells of the blood vessels of the liver and kidney, and multinucleate oocysts have been observed.

Haemogregarina myoxocephali n.sp. from the longhorn sculpin, Myoxocephalus octo-decimspinosus, and Haemogregarina urophysis n.sp. from the white hake, Urophysis tenuis, are described. Two other haemogregarines sens lat. from species of Rana and Bufoamericanus are described, Haemogregarina aeglifini Henry is recorded from a new host, Gadus callarias from off Labrador, Haemogregarina platessae Lebailly from Pseudopleuronectes americanus and Haemogregarina bigemina Laveran & Mesnil from the eel pout, Zoarces angularis, the hosts being new.

Plasmodium catesbiana n.sp. from Rana catesbiana from the Back River, Montreal, is a small species, with ‘signet ring’ and amoeboid trophozoites, schizonts with up to eight merozoites clustered round coarse pigment granules and gametocytes showing slight sexual dimorphism. Plasmodium bufonis n.sp. occurs in Bufo americanus from Laval des Rapides. The schizonts are large, oval, and give rise to eight merozoites arranged en barillet, the pigment usually being at one pole. Possibly micro- and macromerozoites may be produced. Macrogametocytes are oval and deep-staining; microgametocytes are vermicular. Both have pigment.

A haemosporidian, different from but probably allied to Haemogregarina bigemina, is described from the black sea bass, Centropristis striatus.

Haemoproteus laurentiae n.sp. occurs in Bufo americanus from the banks of the St Lawrence at Montreal South and at Lake Manitou. Its pigment is characteristic, consisting of rod-like or bacilliform distributed granules. Haemoproteus lavalia n.sp. from Bufo americanus, from Laval des Rapides, has pigment restricted to curved bands of rounded to somewhat angular granules. Uninucleate parasites have been observed in extremely few endothelial cells of the lungs. Haemoproteus lanoraiea n.sp. from Bufo americanus, from Lanoraie, has very pale yellow to light brown pigment granules, densely crowded at one pole and forming a compact granular cap. Oval parasites have been found in endothelial cells of the lungs.

Leucocytozoon salvelini n.sp., parasitic in the leucocytes of the speckled trout, Salve-linus fontinalis, is described.

Dactylosoma salvelini n.sp., parasitic in Salvelinus fontinalis from a Laurentian stream, is the second species of Dactylosoma to be described and the third to be notified from fish. It has fan- to wedge-shaped schizonts producing eight merozoites. Its gametocytes are not markedly different from one another in shape but differ in cytoplasmic staining and in nuclear structure. Dactylosoma sylvatica n.sp., parasitic in Rana sylvatica from near Quebec City, produces eight merozoites and has oval and reniform gametocytes.

The morphology of a Microfilaria from Rana sylvatica is described.

The effects of the Protozoa on the host cells are described for each organism, and some differential leucocyte counts for comparable normal and parasitized Amphibia are given in the concluding section.

Experiments are described on the inactivation by gamma-rays, X-rays, and alpha-rays of the viruses of tomato bushy stunt, tobacco necrosis, tobacco ringspot, tobacco mosaic and potato virus X. Within the errors of the experiment the inactivation curves appear to be exponential, and the inactivation doses increase in the order gamma-rays, X-rays, of wave-length 1·5 A., X-rays of wave-length 8·3 A., and alpha-rays.

A theory is given explaining these results and correlating the inactivation dose with the virus size. Estimates of the sizes of the viruses obtained from the radiation experiments he within the range of the sizes given by other methods, but are somewhat lower than the most probable sizes. Possible explanations of the discrepancy which are discussed are (a) the virus particle is not the molecule, in the sense of the smallest infective unit, or (b) certain structural changes in the virus molecule produced by the radiation may still leave it infective. Some of these may perhaps show themselves as mutations.