Thin sections of Trypanosoma cruzi in tissue cultures and from blood agar medium have been examined with the electron microscope.

In the leishmania and crithidia forms of the parasite a neat separation of kinetonucleus and blepharoplast has been obtained and these structures are described. The blepharoplast is the row of basal corpuscles which give origin to the axial fibres of the flagellum.

Division of the parasite seems to begin in the basal corpuscles; it is followed by binary division of the kinetonucleus and only later by fission of nucleus and cytoplasm.

During the development of the leishmania into the crithidia form, the kinetonucleus and basal bodies are dislocated towards the posterior half of the trypanosome. The migration of these two structures and the consequent lengthening of the flagellum causes the surface membrane of the flagellum to be pushed inwards to form a deep invagination, so that the flagellum comes to the surface of the body and is separated from it along its whole length by its own sheath.

In the adult form of the parasite a great vacuole is formed near the posterior tip of the trypanosome. It has no definite structure in the electron microscope, is transparent and seems to be filled with a liquid content. The basal corpuscles are situated in this region near the wall of the vacuole. The typical structure of the kinetonucleus could not be identified with certainty in these forms; it seems to be altered by the formation of the vacuole.

The vacuole is crossed by a fibre system which comes from the body of the trypanosome and is often dislodged by the size of the vacuole. This fibre system ends in a sharply pointed process of varying length.

The cost of reproduction of figures was defrayed by the Instituto de Biofísica da Universidade do Brasil.

1. The genus Meteterakis is reconstituted with eight species: M. govindi, M. louisi, M. baylisi, M. longispiculata, M. cophotis, M. japonica, M. mabuyi and M. triaculeata.

2. M. cophotis, M. japonica and M. longispiculata were previously placed in the genus Spinicauda.

3. M. mabuyi was previously in the genus Africana.

4. M. triaculeata was previously in the genus Ganguleterakis.

5. M. baylisi and M. louisi are new species.

6. Spinicauda bufonis and, probably, Africana varani are considered synonyms of M. govindi.

7. Africana howardi is considered a synonym of M. japonica.

8. A list of the remaining species in the genera Africana and Spinicauda is given.

1. An examination of the cuticle of Oxyuris equi has revealed the presence of previously unidentified structures. The layers of the cuticle of this nematode have been renamed.

2. The cuticle of Strongylus equinus has been examined in a similar fashion and, whilst the basic nomenclature of the various layers has been retained, previous descriptions of the individual layers have been modified and extended.

3. Further evidence is put forward in favour of the presence of pore canals in the cuticle of Ascaris lumbricoides.

The following new species of Ixodes from eastern Africa are described and figured: I. rotundatus, I. auriculaelongae, I. nchisiensis, I. latus, I. loveridgei, I. spinae, and I. euplecti.

The female of I. oldi is redescribed and the hitherto unknown male and nymph are described and figured. Some consideration is given to two specimens from Uganda which differ in certain particulars from typical specimens from East and West Africa.

The life cycle and pathogenicity of a strain of Eimeria isolated in Great Britain from turkey poults by single cell inoculation are described and, using the criteria laid down by Tyzzer, the species is identified as E. adenoeides.

The life cycle is of the same general pattern as in other Eimeria species, consisting of two asexual and one sexual generations.

The organism is highly pathogenic for young poults, a dose of 200,000 oocysts producing 100 % mortality in 3-week-old birds and smaller doses causing reduced weight gain. Birds 11 weeks old resisted a dose of 3 million oocysts.

The gross and microscopic pathology of the infection is described. No changes were found in the blood picture.

1. A short note is given on Pterygosoma hystrix Lawrence, 1935, amplifying the original description and extending the known range of variation.

2. The hitherto undescribed male, larva, protonymph and deutonymph of Pterygosoma gerrhosauri Law, 1935, are described and figured.

3. The protonymph and deutonymph of Pterygosoma bicolor Law, 1935, are described and figured, together with a record of variation in the female.

This paper gives an account of the mature eggs and the miracidium of Paryphostomum mehrai obtained from experimentally infected white rats, which were fed with the cysts of Cercaria mehrai obtained from naturally infected as well as artificially infected snails of the species Indoplanorbis exustus. The metacercariae develop into the adults in the intestine of the host in a period of 20 days, after which the adults begin to lay their eggs, which are passed out with the faeces of the host. The molluscan phase of the life cycle involves the gradual development of the miracidium larva after its penetration into the molluscan host into a mother rediae. The mother rediae, not more than three to five in number, were observed in the preoesophageal region of the snail host. They produce large numbers of daughter rediae, which were found migrating towards the liver mass. The daughter rediae, after fixing themselves in the liver mass, undergo further development and produce large numbers of cercariae. The entire process, from the entry of the miracidium until the cercariae are matured takes about 8 weeks.

1. Methods are described for the isolation and maintenance of a pure strain of Eimeria mitis.

2. The prepatent period of the infection in chicks was 101 hr. The mean dimensions of the oocysts were 15·38 × 13·83μ, and sporulation occurred after 48 hr. at 60° F. (15·5° C.). The production of oocysts following infection with known numbers of oocysts is recorded.

3. When 500,000 or more oocysts of E. mitis were given to chicks aged 6, 17 or 26 days the growth rate of the birds was markedly reduced. Young chicks were most susceptible and a few deaths occurred when 6-day-old chicks received 2·5 million oocysts. E. mitis is unlikely to be of pathological importance under normal conditions of good husbandry practice.

4. Pathological lesions due to this species of Eimeria were not found in sections of intestinal tissues.

5. Developmental stages of this parasite were found throughout the whole of the small intestine.

6. The growth-retarding effects and oocyst production by E. mitis were controlled when 0·2% sodium sulphadimidine was given in the drinking water.

1. A brief outline of the life cycle of a species of Nosema parasitic in Saturniid moths is given. It is of the normal type.

2. The structure of the spore is described, and from electron microscopy evidence is presented which supports the theory that the sporoplasm is injected into the host's tissue.

3. The volume of the spore is affected by the ambient medium, by the pretreatments of fixation and of desiccation, by the site of development within the host and by the age of the host.

4. These results have been discussed with reference to the use of spore size as a diagnostic character in the classification of the Microsporidia. It is concluded that spore size is not a reliable character for taxonomic purposes.

A male and a female of a species of Syngamus were found in copula in the small intestine, about 1 in. from the gizzard, of a fieldfare (Turdus pilaris) which had been shot accidentally. The nematodes were well preserved and were undamaged. Eighty-four small tapeworms, of two different genera, were also present in the intestine. Neither the tapeworms nor the nematodes were attached to the intestinal wall.

1. The male of Ixodes rothschildi is described for the first time from the burrows of Fratercula arctica grabae at Skokholm, Wales.

2. The species described as I. rothschildi by Zumpt is now considered as a new species, I. diomedeae.

1. Maturation of the plerocercoid of the pseudophyllidean cestode Diphyllobothrium sp. and the metacercaria of the strigeid trematode Diplostomum phoxini follow a similar pattern, which may be divided into the following phases: (1) cell multiplication; (2) segmentation or body shaping; (3) organogeny; (4) early gametogeny; (5) late gametogeny; (6) egg-shell formation and vitellogenesis; (7) oviposition.

2. Cytological or histochemical criteria have been developed by means of which each developmental phase may be recognized. Development in vitro may be considered comparable with that occurring in vivo if the same phases are completed with the same incubation time and without the appearance of cytological abnormalities.

3. The cell multiplication phase is characterized by high mitotic activity. This activity in vitro can be evaluated by incubating larvae after 24 hr. culture for a standard time (5 hr. Diphyllobothrium; 4 hr. Diplostomum) in 10−4 colchicine and comparing the number of mitoses seen in a defined area of an aceto-orcein squash with those found in tissue matured in vivo for the same period. Use of this criterion enables the growth-producing properties of a medium to be assessed after 24 hr. culture.

4. Phases 2–4 are characterized by the appearance of the tubular genitalia, the rudiments of which are readily recognized in aceto-orcein squashes or whole mount preparations.

5. The presence of spermatids and mature spermatozoa (phases 4–5) may be detected in aceto-orcein squashes or in fresh tissue teases. The quantity and activity of spermatozoa also serve as important criteria.

6. Recognition of phase 6, egg-shell formation, is carried out by means of diazo reagents which give orange or orange-red reactions with the phenolic egg-shell precursors in the vitellaria, as seen in whole mount preparations. Abnormal egg-shell development is reflected in the failure of vitellaria to give a normal diazo reaction.

7. The appearance of eggs which are macroscopically normal constitutes the final maturation phase. Early detection of eggs (especially abnormal ones) is facilitated by the use of the diazo reaction or the catechol test for polyphenol oxidase.

8. Embryonation and hatching of eggs to produce morphologically normal infective coracidia or miracidia serve as a final criteria.

9. Criteria for the maintenance of the adult condition are also considered.

1. Standard conditions are described for preparing suspensions of washed Trypanosoma lewisi and T. equiperdum in modified Ringer–phosphate solution.

2. Oxygen consumption was measured with differential manometers, using microflasks containing 2–5 × 107 trypanosomes in 0·9 ml. of reaction mixture. Measurements of oxygen uptake were carried out at 37° C.

3. T. lewisi respired slowly in the absence of substrate for up to 2 hr. The trypanosomes suffered little damage when stored at 5° C. for 24 hr. without substrate. No oxygen uptake was observed with T. equiperdum in the absence of substrate. The trypanosomes were viable after 24 hr. at 5° C. with glucose or glycerol as substrate, but not in the absence of substrate.

4. With glucose as substrate, the rate of oxygen consumption by T. lewisi increased with the age of infection. This change was more marked with glutamine as substrate.

5. With glucosamine as substrate, the oxygen uptake of T. lewisi was at a slightly lower rate than with glucose. The rate of oxygen uptake was still lower with Na l-glutamic acid, asparagine, aspartic acid, casein hydrolysate, yeast extract and Difco Bacto-peptone. Thirteen other amino-acids had no effect on the motility of the trypanosomes.

6. With glycerol as substrate, the oxygen uptake of T. equiperdum was at a slightly lower rate than with glucose. The rate of oxygen uptake was very low with yeast extract, casein hydrolysate and Difco Bacto-peptone. No oxygen uptake or motility was recorded with glutamine, Na l-glutamic acid, glucosamine, asparagine, aspartic acid, dl-alanine, or Na acetate. Thirteen other amino-acids had no effect on the motility of the trypanosomes.

7. Ammonia was liberated from glutamine by adult and reproductive phase T. lewisi.

1. The oxygen uptake of Trypanosoma lewisi and T. equiperdum was measured with differential manometers using microflasks of 5 ml. capacity. Each flask contained 2–5 × 107 trypanosomes.

2. The oxygen uptake of trypanosomes in heparinized infected blood was compared with that of washed trypanosomes suspended in Ringer–phosphate–glucose solution with or without added serum or blood. With T. lewisi, the oxygen uptake began at a higher rate in the presence of blood or serum than with Ringer–phosphate–glucose solution. With T. equiperdum, the oxygen uptake in the presence of blood or serum began at almost the same rate as with Ringer–phosphate–glucose solution, but the rate of oxygen uptake decreased more rapidly in the absence of blood or serum than when it was present.

3. High concentrations of iodoacetic acid (e.g. 3·3 × 10−2m) caused an increase in oxygen uptake when tipped into heparinized normal rat blood. Similar concentrations caused an inhibition of oxygen uptake when 2·0 × 10−4m methylene blue was also present or when the blood had been treated with sodium nitrite to convert haemoglobin into methaemoglobin.

4. Iodoacetic acid caused little inhibition of oxygen uptake when T. lewisi was suspended in Ringer–phosphate solution containing glutamine or glutamine plus glucose, or when heparinized infected blood was tested. Inhibition was greatest when the substrate was glucose, while glucosamine, glycerol, or glucose plus serum gave intermediate results.

5. Iodoacetic acid caused least inhibition of oxygen uptake when T. equiperdum was suspended in Ringer–phosphate solution containing glycerol, or when heparinized infected blood was tested. Inhibition was greatest when the substrate was glucose, and was slightly less marked when the substrate was glucose plus serum or glucose plus glycerol.

6. Neoarsphenamine inhibited the oxygen uptake of T. lewisi to a similar extent whether glucose or glutamine was present.

7. Neoarsphenamine and reduced stovarsol thioglycollate inhibited the oxygen uptake of T. equiperdum slightly less when the substrate was glycerol than when it was glucose. Sodium arsenite was as active as reduced stovarsol thioglycollate when the substrate was glucose, but 10−4m sodium arsenite had little effect when the substrate was glycerol.

1. Evidence from previous literature shows that puppies are commonly infected with larvae of Toxocara canis at birth and that prenatal infection can be produced by feeding embryonated eggs to pregnant bitches.

2. Observations on fifty-eight dogs in Brisbane showed that all of twenty-nine puppies 1–6 months old were infected, while only three out of twenty-nine dogs over 6 months old were infected.

3. In naturally infected puppies, 1–3 weeks old, it was found that at birth third-stage larvae were present in the lungs. Third-stage larvae continued to appear in the lungs for the first week of life; their length was 0·6–1·3 mm.

4. Third-stage larvae were found in the stomach on the day after birth; at 3 days after birth fourth-stage larvae were found in the intestine.

5. It appeared likely that the second moult occurs in puppies before birth, and that the third moult takes place at a length of 1·0–1·3 mm. in the lungs and stomach within the first week of life.

6. By the beginning of the second week, fourth-stage larvae were fully grown and had commenced the fourth moult at a length of 5–7 mm.

7. Throughout the second and third weeks, adults grew rapidly, reaching a length of about 67 mm. by the end of the third week, but no eggs had appeared in the faeces at this time.

8. Experimental infection of mice with eggs showed that the larvae were distributed to the somatic tissues, few reaching the alimentary tract. The larvae did not progress beyond the second stage in the tissues of mice.

9. Experimental infection of dogs with eggs showed that in dogs over 5 weeks old the larvae were distributed to the somatic tissues and did not reach the alimentary tract. The larvae did not progress beyond the second stage, though some of them showed signs of commencing the second moult. In contrast, 1 to 3-week-old puppies infected in the same way were found to harbour larvae in the alimentary tract. Though some of these larvae were probably derived from a naturally acquired prenatal infection, it was evident from the progress of development that the experimental infection resulted in the presence of second-stage larvae in the liver and lungs and that these larvae underwent the second moult, commenced development as third-stage larvae in the lungs, migrated into the stomach and developed to the adult stage in the intestine.

10. Experimental infection of dogs and foxes with mice harbouring second-stage larvae in the tissues showed that, in some instances, development of larvae proceeded in the alimentary tract. No evidence of somatic migration was found in dogs infected in this way, but in foxes second-stage larvae were found in the lungs.

11. The structure and development of the second, third and fourth stage is described in detail and found to resemble closely the development of T. cati larvae (Sprent, 1956). Second-stage larvae from dog tissues had a length of 0·34–0·44 mm. and the second moult occurred at a length of 0·37–0·44 mm. Third-stage larvae varied in length from 0·46 to 1·36 mm., and the third moult occurred at a length of 0·98–1·3 mm. Fourth-stage larvae measured 1·2–6·3 mm., though moulting fourth-stage larvae were observed up to a length of 7·4 mm. Sexual differentiation occurred during the fourth stage and was evident at a length of about 1·5 mm.

12. The migratory behaviour of the larvae of T. canis and T. cati is compared and discussed in relation to their wide range of hosts. It is concluded that differences in migratory behaviour are adaptations to prevailing modes of nutrition and it is suggested that the somatic migration occurring in dogs is an adaptation to the non-predatory habits of this particular host.

1. The development of resistance to metachloridine (3-metanilamido-5-chloropyrimidine) was studied in two clones of Plasmodium gallinaceum derived from single erythrocytic parasites and maintained by serial inoculation in young chicks. Resistance developed with equal facility and similarly in the two clones.

2. In thirteen strains of these clones an enhancement of resistance was obtained after three to five courses of treatment, each of seven doses of metachloridine over a period of 3½ days.

3. The effect of the size of the inoculum (2·5 × 107–109 parasites), and of the dose of drug upon the rate of development of resistance was studied. Although the number of courses of treatment required to produce an enhancement of resistance was not always related to the size of the inoculum, with the largest inoculum an enhancement of resistance was observed after the minimum number of courses of treatment (three), whereas with the smallest inoculum no enhancement of resistance was obtained. The rate of the development of resistance did not appear to be related to the size of the dose of drug.

4. In some strains the increase in resistance was sudden, whereas in others it was more gradual. Resistance was retained when parasites of a newly resistant strain were transmitted through Aëdes aegypti or maintained for 43 days in the absence of the drug.

5. A comparison of the development of resistance in populations of normal parasites, and of populations composed of mixtures of known numbers of resistant and normal parasites, indicated that the pattern of the development of resistance in normal populations could be explained by the selections of mutations of a frequency of less than 1 in 5 × 107, or probably less than 1 in 109 parasites.