Nuclear division in the trophic stages of Iodamoeba butschlii (Prowazek, 1912) Dobell, 1919

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.