1. An account on the cercariae found in Melanopsis praemorsa common in the River Yarkon (Israel) is given.

2. A new species of Cercaria of the Pleurolophocerca group, Cercaria orospinosa, is described.

3. The development of C. orospinosa to the stage of metacercaria in the tadpole of Bufo viridis shows its affinity to the subfamily Cryptogoniminae (Hetero-phydae).

4. An artificial genus Velocercaria is proposed to comprise cercariae which have common morphology with Cercaria orospinosa and are characterized by the same type of tail-fins.

Trypanosoma cruzi has been examined with the electron microscope. Crithidia and metacyclic forms of a blood agar culture have been studied and compared with the adult tissue forms, obtained in tissue cultures, from the same strain.

In all the forms studied, the internal structure of the body is not revealed because it is too thick for electron penetration. In places where a good penetration has been obtained the cytoplasm shows a fine striation in spiral or parallel arrangement. This striation can be digested with trypsin or by prolonged osmic acid fixation.

Dense spherical bodies of variable size can also be observed in the body portion. They can be dissolved with xylene.

The whole body of the trypanosome is covered by a fine, transparent sheath.

The flagellum is formed by the axoneme which consists of five or nine fibres. It can be followed throughout the whole length of the metacyclic and of the adult tissue forms. In the crithidia forms of the blood-agar culture, it disappears in the anterior part of the body. The whole flagellum is covered by a fine sheath. The axial fibre bundle can be digested with trypsin or by prolonged osmic-acid fixation. Both, the striation and the fibre bundle are contractile structures which could explain the movements of the trypanosome.

Some dividing forms are also described.

This paper contains a discussion of the generic and specific characters of Tricho-nympha and Pseudotrichonympha, with a detailed account of the morphology of P. sertaneja n.sp. from a new species of Rugitermes.

The basic generic and specific characters of each organelle of Pseudotrichonympha are considered in detail. The genus Pseudotrichonympha has been separated from Trichonympha by the absence of the rostral articulation (citartrosi) and parabasal body. But in at least two species of Pseudotrichonympha a parabasal body has been found, and as Grassi himself believed that citartrosi, however feebly developed, must exist in all Pseudotrichonympha, the taxonomic position of Pseudotrichonympha needs further investigation.

The morphology of P. sertaneja n.sp. has the basic generic characters. The specific characters are discontinuous myonemes, oblique instead of longitudinal leiotropic striae, flagella of the first series covering not only the neck but the upper portion of the body, flagella of the second series confined to the basal part of the anterior triangular area of the body, flagella of the third series very short and of uniform size and simple outline of the ectoplasm.

The flagellate is regarded as a new species, named P. sertaneja n.sp. The host is a new species of Rugitermes from São Paulo, Brazil.

An illustrated account of a new species of Stephanonympha from the Brazilian termite, Neotermes hirtellus Silvestri, is given.

An historical introduction provides concise accounts of the previously described species of Stephanonympha.

The morphology of the new Stephanonympha is described in detail and illustrated.

Differential characters from previously described species of Stephanonympha are noted, the conclusion being that the Stephanonympha, of Neotermes hirtellus is a new species from a new host, to which the name Stephanonympha campinae n.sp. is given.

An account is given of the general structure of Proteocephalus pollanicola. The genital system is dealt with in greater detail. The characteristic features of the species are enumerated.

The male portion of the reproductive system consists of 60–75 testes in a single layer; vasa efferentia with a lining epithelium; a wide, coiled vas deferens; a small cirrus-sac; a coiled ejaculatory duct and a short cirrus. A description is given of the histological structure of the male ducts.

The vagina opens anterior to the cirrus-sac. A well-developed vaginal sphincter is present. The seminal canal communicates with the oviduct and the uterine canal. An oocapt is present; the transverse vitelline ducts and the ovary open into it. A few unicellular glands are present hi the vicinity of the oocapt; these possibly represent Mehlis's gland. An ootype is absent. The histological structure of the female ducts is described.

Data concerning the life cycle of the various species of the genus Trichuris are somewhat controversial. The present paper is devoted to the study of T. muris, a common parasite of the caecum of wild house-mice and rats. The possibility of transfer of T. muris in the laboratory mice would enable the author to solve various contradictory points.

Contrary to results previously published, cortisone did not cause a rapid increase of parasitaemia in mice or hamsters infected with P. berghei, and in some cases it had an inhibitory effect. The existence of a humoral agent restricting the multiplication of the parasites in the peripheral blood was suggested.

In April 1953, several specimens of the common commercial mullet, Mugil cephalus L., heavily infested with cysts in the body cavity, were received. In May, June and July 1953, several specimens of the estuarine catfish, Netuma australis (Gunther) (Family Ariidae), similarly infected, came to hand. All specimens were taken from the lower reaches of the Brisbane River, Brisbane.

In 1915 Glaser demonstrated for the first time that a nuclear polyhedrosis of a lepidopterous larva (Lymantria dispar), was induced by an invisible filterable virus isolated from the blood of diseased larvae. Nuclear polyhedroses of the larvae of over a 100 insect species are now known, and those of them which have been investigated have been shown to be due to viruses. In these polyhedroses the nuclei of susceptible cells, hypodermis, tracheae, fat and blood cells, etc., enlarge and become packed with infectious crystalline inclusion bodies, the polyhedra, from which the diseases get their name. The pupae and imagos of these insects are not generally susceptible to polyhedral virus diseases, and so far no nuclear polyhedrosis of imaginal tissues in the larvae has been reported. This has led to the suggestion that imaginal tissues are not susceptible to polyhedral virus diseases.

Experiments were designed to dissociate the effect of Eperyfhrozoon coccoides on the blood of mice from the effect of splenectomy. Both agents caused a decrease in number of red blood cells which was followed by an increased production of reticulocytes. The anaemic condition caused by the eperythrozoa persisted for more than 230 days after splenectomy, and parasites were seen in fluctuating numbers at intervals throughout this period.

At the height of infection, red blood cells were more fragile than normal in hypotonic saline and the blood clotted more rapidly than normal. No breakdown products of haemoglobin were detected in the urine or serum, and no haemolysins or haemagglutinins were detected in the serum. The white cell count was usually increased after heavy infections, the chief increase being in the number of myelocytes and other immature cells.

The action of pyrimethamine, sulphadiazine, proguanil and its active metabolite CPT, and 2:4-diaminopteridines against infections of Plasmodium berghei in mice was antagonized by P–aminobenzoic acid and by pteroylglutamic acid. Antagonism was in some instances detected only when P–aminobenzoic acid was given in solution in the drinking water as well as being injected subcutaneously. No antagonism was detected with a number of amino acids and nucleic acid derivatives.

As all of the above group of drugs can be antagonized by P–aminobenzoic acid and by pteroylglutamic acid, it would seem that they are alike in their mode of action. There must, however, be some differences between the mode of action or absorption of these drugs because species of Plasmodium that are very sensitive to the action of one of these drugs are frequently not very sensitive to the action of others.

As P. berghei is dependent on p–aminobenzoic acid, it is suggested that it can utilize this compound in the synthesis of pteroylglutamic acid to a greater extent than can P. gallinaceum, and that it resembles P. knowlesi more than other species of Plasmodium.

1. The feeding habits of second- and third-instar larvae of Neottiophilum praeustum have been observed and show that this species is a true parasite of birds and feeds by sucking the blood of nestlings.

2. If they are too numerous the larvae may kill the nestlings. Although they will continue to feed upon dead birds, and even penetrate into the viscera, such food is unsuitable for the development of the larvae and they become greatly distended and die within a few days.

3. The morphology of the hitherto unknown second-instar larva is described and is compared with that of the third instar.

4. Within the puparium of Neottiophilum praeustum there is a fourth moult resulting in the formation of a cast prepupal cuticle which resembles that described by Snodgrass in Rhagoletis pomonella and is much better developed than the prepupal cuticle in Calliphora erythrocephala.

5. The better development of the prepupal cuticle in the acalypterates than in calypterates indicates that the presence of a prepupal stage in the cyclorrhaphous Diptera is a primitive character and is progressively reduced until in the higher families it is almost vestigial.

In strains of Plasmodium gallinaceum passaged by blood-inoculation, through young birds treated with small, but effective doses of proguanil, sulphadiazine or 2:4-diamino-6:7-diisopropylpteridine, the numbers of gametocytes produced were much greater than in the parent strain passaged by the same method.

The effect of the drugs upon gametocyte production appears to be a long term one, since no change in gametocyte numbers was observed in birds treated with proguanil or sulphadiazine for only a few days.

The relationship of these drugs to nuclear division and the synthesis of nucleic acids is discussed in the light of the observed increase in gametocyte-production in drug-treated strains of P. gallinaceum.

1. A method, based on that devised for E. histolytica by Dobell (1947), was worked out for testing the action of drugs upon E. invadens.

2. The sensitivity of di- and monobacterial strains of E. invadens to emetine was determined, and of a dibacterial strain to the quinaldines A 352, A 356 and A 404. E. invadens was killed by emetine at concentrations of 1/50,000–1/100,000, A 352 or A 356 at 1/100,000, and A 404 at 1/10,000. The strains of E. invadens used in the present tests are thus less sensitive to emetine than is E. histolytica, but the sensitivity of the two species to the quinaldines is similar.

3. A strain of E. invadens which was maintained for 9 months in the presence of increasing concentrations of emetine, did not become resistant to the drug.

I am indebted to Dr A. Bishop for much advice and criticism; to Dr J. D. Fulton for a culture of Bacterium coli A'; and to Dr J. Walker for supplies of the compounds A 352, A 356 and A404. The work has been financed by the Medical Research Council.

The genus Ischnopsyllus Westwood, comprising at the moment sixteen species and subspecies, is rather a heterogenous group. Although I am reluctant to split this relatively small genus, a certain degree of division is unavoidable. First, I. grahami Waterston certainly does not belong to the genus Ischnopsyllus, and since this species does not fit any other genus of bat-fleas, a new genus has had to be erected for it (see below, where a new subspecies of grahami is also described). Secondly, the hexactenus-group of Ischnopsyllus is sufficiently distinct from the rest of the genus to make it desirable to restore, as a subgenus, the genus Hexactenopsylla Oudemans, which was synonymized with Ischnopsyllus by Dalla Torre in 1924.

In connexion with studies on bat malaria carried out by Prof. G. Mer and Dr N. Goldblum at the Malaria Research Station of the Hebrew University, a great number of ectoparasites of bats were submitted to us for identification. Together with material collected by us, over a thousand nycteribiids, streblids, Hemiptera, Siphonaptera, ticks and mites were examined.