1. Rickettsia-like bodies are recorded from the reduviid bug, Triatoma rubrofasciata.

2. These Rickettsiae are capable of being transmitted hereditarily and have been found in the unhatched embryos and larvae of the bug.

3. They produce pathological lesions in laboratory animals and can be maintained for at least five passages through guinea-pigs.

Argulus Foliaceus has a remarkably wide distribution, and is found throughout Europe. A. coregoni, which is another European form of the Argulidae, has been recorded in England from such localities as the Birmingham Canal; Barble, Leicestershire; Berkshire Trout Farm; the River Wharfe, Yorkshire; Tring Reservoirs; the Thames; the River Frome in Somerset; and the River Lune.

1. The anatomy of the adult miracidium of Parorchis acanthus is described.

2. Development of the miracidium and of the succeeding larval stages has been followed.

3. Cleavage of the fertilized egg gives rise to an ectodermal and a propagatory cell. The former gives rise to the soma, and the latter, after contributing a few small cells to the body of the miracidium, becomes the germ cell.

4. This germ cell develops in the same way into the first generation redia while still in the body of the miracidium.

5. The fully formed miracidium contains a single fully formed redia when it penetrates the intermediate molluscan host.

6. In the intermediate host the miracidium disintegrates and second generation rediae are formed from the germ cells in the body cavity of the parent redia.

7. The germ cells in the body cavity of the daughter redia give rise to cercariae by a similar process of embryonic development to that found in preceding generations.

8. The germ cells in the cercariae become differentiated into the adult genitalia.

9. No evidence has been found to show that rediae or cercariae are derived from cells in the wall of the redia.

10. No ovary, maturation process, parthenogenesis, or fertilization takes place in any of the larval stages, but germinal lineage is apparent throughout the life cycle.

From 1931 to the middle of 1936 we occasionally examined the gut contents of the centipede Cormocephalus dentipes, procured from Calcutta and its suburbs. In the intestine we have often found a coccidium belonging to the genus Adelina. Species of Adelina are on record from arthropod and annelid hosts; but since Schellack (1913) described in detail the life history of A. dimidiata from Scolopendra cingulata, no account of any other species from a myriapod has been given.

If the normal molluscan host of Fasciola were a species of Lymnaea it should be possible readily to produce experimental infection in that species. Although adult flukes have been reared from larvae found naturally in different species of Lymnaea in various countries, great difficulty has been experienced in producing experimental infection of these same species of Lymnaea. In fact, although the factors governing the successful completion of the life cycle are not known, the ease with which, according to text-books, the cycle may be followed experimentally, is contrary to experience in both Europe and warmer climates.

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.

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.

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?).

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.)