Shiga distinguished two species; a larger pathogenic species with a somewhat active movement, and a small harmless species with a somewhat sluggish movement. Bowman mentions two varieties, Strong and Musgrave (1900) two species--the pathogenic _Amœba dysenteriæ_ and the non-pathogenic _Amœba coli_; Jäger (1902) and Jürgens (1902) mention at least two species. In the following year (1903) a work by Schaudinn was published which marked a real advance. This, in conjunction with the establishing of a special genus (_Endamœba_ or _Entamœba_) for human intestinal amœbæ first by Leidy[11] and then by Casagrandi and Barbagallo,[12] for the time cleared up the confused nomenclature, the old name _Amœba coli_ being retained for the harmless intestinal amœbæ of man, whereas the pathogenic species was designated _Entamœba histolytica_. The history of more recent work is incorporated in the accounts of the entamœbæ given below. [11] “On _Amœba blattae_,” _Proc. Acad. Nat. Sci._, Philadelphia (1879), xxxi, p. 204. [12] “_Entamœba hominis_ s. _Amœba coli_ (Lösch).” _Annali d’Igiene speriment._ (1897), vii, p. 103. See also further remarks on p. 34. *Entamœba coli*, Lösch, 1875, emend. Schaudinn, 1903. Syn.: _Amœba coli_, Lösch, 1875. _Entamœba hominis_, Casagr. et Barbag. 1897. The amœboid trophozoite, according to Lösch, measures 26 µ to 30 µ and upwards; according to Grassi 8 µ to 22 µ; according to Schuberg 12 µ to 26 µ. A separation of the body substance into ectoplasm and endoplasm is only perceived during movement. The pseudopodia, which are generally only protruded singly, are broad and rounded at the end (lobopodia) and are hyaline, while the remainder of the body is granular. The ectoplasm is less refractile than the rest of the cytoplasm; it also stains less intensely (fig. 1), and is best seen on protrusion of a pseudopodium. Red blood corpuscles are rarely, if ever, found ingested in the cytoplasm. [Illustration: FIG. 3.--_Entamœba coli_: life-cycle, _a_-_e_, stages in binary fission; _A_-_D_, schizogony, with formation of eight merozoites; 2–10, cyst formation or sporogony, with formation of eight nucleate cysts. (After Castellani and Chalmers)] The nucleus is vesicular, and is spherical when inactive, measuring 5 µ to 7 µ, with a thick nuclear membrane. In the centre of the nucleus is a chromatinic body or karyosome or sometimes several small nuclear bodies formed of plastin and chromatin; the remaining chromatin is arranged on the achromatic network in the form of fine granules, especially thickly deposited on the nuclear membrane.