Studies of Endamoeba blattae (Bütschli)

Researches on the intestinal protozoa of monkeys and man

1. The life-history of Entamoeba coli (from a marmoset, several macaques, and Man), as observable in cultures, is here described and illustrated. It is found to be similar, in general outline, to that of E. histolytica, but to differ considerably in its excystation and metacystic stages.

2. At excystation, the entire contents of the cyst usually escapes, as a single multinucleate amoeba, through a large opening in the cyst wall, which is composed of two layers.

3. Normal ripe cysts frequently lose 1 to 4 of their 8 original nuclei before hatching, thus becoming “infranucleate” (i.e. containing only 4 to 7 nuclei instead of the “typical” 8).

4. During the metacystic stages no nuclear divisions occur. The hatched amoeba eventually produces, by a series of binary cytoplasmic fissions with random nuclear distribution, as many uninucleate amoebulae as it originally contained nuclei.

5. An originally 8-nucleate cyst may therefore produce 8 amoebulae finally –never more: but owing to the frequent development of infranucleate forms, it often produces only 7, 6, 5, or 4.

6. Development is complicated by occasional division into two within the cyst before hatching, or at the moment of hatching—such divisions being seen in both “typical” and “infranucleate” cysts; and also by the occurrence of supernucleate cysts (containing more than 8 nuclei), which are often viable but usually develop in an infranucleate condition. Consequently, amoebae containing any number of nuclei from 1 to 8—or even more—may hatch from the cysts of this species (unlike those of any other hitherto described).

7. The uninucleate amoebulae resulting from the metacystic divisions are young trophic amoebae—not gametes—and no sexual stages occur in the life-cycle. Division of the trophic amoebae is briefly described and figured.

8. The life-cycle of E. coli is finally compared with that of E. histolytica and related species: the relevant observations of other workers are briefly analysed: and the taxonomic implications are noted.

A memorandum is added on the genus Entamoeba, in an attempt to clarify the nomenclatural and taxonomic confusion created by Opinion 99 promulgated by the International Commission on Zoological Nomenclature. This leads to the conclusion that the Opinion itself is a dead letter, though the genus Entamoeba still lives and should therefore be retained, for the time being, with E. coli Casagrandi & Barbagallo, 1895, as its type.

Nuclear division in nine species of small free-living amoebae and its bearing on the classification of the order Amoebida

A study of nine species of small free-living amoebae has been made under standardized and reproducible cultural conditions, by a new method that enables specimens in all stages of division to be obtained easily. In all species the resting nucleus shows a Feulgen-negative nucleolus and Feulgen-positive chromatin granules. Nuclear division in these species and in other amoebae described by other workers is of two main types on which it is proposed to create two new families— Schizopyrenidae and Hartmannellidae. In Schizopyrenidae, the type genus Schizopyrenus n.g. and two other genera, Naegleria and Didascalus n.g., are defined. Naegleria gruberi, Didascalus thorntoni n.sp., Schizopyrenus russelli n.sp., S. erythaenusa n.sp. and S. atopus n.sp. are described. In Hartmannellidae the type genus Hartmannella is defined. H. glebae, H. rhysodes n.sp., H. leptocnemus n.sp and H. agricola are described. The relation of the proposed classification to previously defined families and genera of amoebae, and its bearing on phylogeny are discussed.