1. Study of the nuclear morphology of a large number of haematoxylin-stained specimens of Iodamoeba bütschlii has permitted description of the process of nuclear division in this organism.

2. The interphase nuclei of the trophozoites were classified into four types (types I to IV) depending on the distribution of the periendosomal granules. The development of the four types of interphase nuclei appears to follow the process of nuclear division.

3. During the early prophase stages the periendosomal granules are incorporated into the endosome. More than twenty small granules are formed from the organizing endosome.

4. In late metaphase stages more than ten, and probably twelve, granules can usually be counted per set of the daughter chromosomes.

5. The centrodesmus may extend beyond the nuclear boundary during the anaphase stages, while the nuclear membrane appears intact.

6. The periendosomal granules reappear by the end of telophase stages when the two daughter nuclei are nearly completely separated.

7. In the freshly separated daughter cell the nucleus may still retain the trailing tail and appear tadpole-shaped, but the periendosomal granules are usually arranged like those in the type I interphase nucleus.

8. The validity of the genus Iodamoeba is re-emphasized on the basis of the characteristic nuclear structures and the unique process of nuclear division as here described for I. bütschlii.

The haplosporidian described is found in the Malpighian tubules of the beetle Gonocephalum arenarium in the Cape Peninsula, South Africa.

With the exception of the germination, which must take place in the digestive tract, the life cycle is completed within the Malpighian tubules. Studied over a period of several years, it has been found that the incidence of infection averages about 5 %.

Six Malpighian tubules connect with the gut, and in an infected insect all six are almost always parasitized to the same degree and by the same forms of the parasite.

1. The cytological study of 4–8 hr. old zygotes of seven species of Plasmodium, i.e. P. gallinaceum, P. berghei, P. cynomolgi, P. gonderi, P. inui, P. knowlesi and P. vivax, revealed a uninucleate condition at the resting phase.

2. Ookinetes of these species at 12–24 hr were uninucleate and of the usual dimorphic form.

3. In the present studies post-zygotic meiosis was demonstrated in the early oocysts of the above seven species of Plasmodium. The times of investigation for the beginning and completion of meiosis in the early oocysts of these species of Plasmodium were as follows:

4. Different forms of spireme at prophases were observed in the early oocysts of the above species of Plasmodium. This fact indicated that each species has its own characteristic form of spireme; for instance, ‘bow-shaped’ in P. gallinaceum, beaded, filamentous net-work in P. cynomolgi.

5. The diploid and haploid number of chromosomes were demonstrated step by step, during the first reduction division in the early oocysts of seven species of Plasmodium.

6. The succeeding nuclear divisions following the post-zygotic meiosis were traced in early oocysts of seven species of Plasmodium. The divisions took place mitotically, giving rise to tetra- to multinucleate oocysts. The haploid group of chromosomes in each species was quite distinct during the different mitotic phases found in these oocysts.

7. The results obtained from the cytological study of different meiotic and mitotic phases found in the early oocysts of seven species of Plasmodium show that the number of chromosomes is a specific character, for instance, P. gallinaceum has a complex of two haploid chromosomes, P. cynomolgi, four; P. gonderi, three; P. inui, four; P. knowlesi, P. berghei and P. vivax, two.

Ribonucleic acid which was normally present in Toxoplasma gondii was found to disappear or become undemonstrable during the action of the dye-test antibodies using cytochemical techniques. A possible explanation for the mechanism of the dye test has been put forward based on this evidence.

A positive Feulgen reaction has been seen in all stages of Toxoplasma gondii. The intense basophilia seen in the intracellular and the extracellular stages is removable by treatment with ribonuclease. Granules which reacted positively with the periodic acid-Schiff technique were found in abundance in the cytoplasm of the cysts, whereas the same granules were not universally present in the intracellular and the extracellular stages at all days of infection. The cyst wall stained with this technique with varying degree of intensity.

It is thought that the variations seen in the individual parasites may be attributed to various causes, for example, strain differences, differences in the reaction of the host to the parasite, differences in the period of infection or to other unknown causes.