Order. Protomonadina, Blochmann.
The smallness of the Protomonadines and their less superficial situation than the Polymastigines, may be the cause that so far as the species occurring in man are concerned, they were formerly less well known. As regards parasitic species, this group may be divided as follows, according to the number of flagella and the presence or absence of an undulating membrane:—
(1) Cercomonadidæ, with one flagellum at the anterior extremity, without an undulating membrane.
(2) Bodonidæ, with two flagella, without an undulating membrane, except in Trypanoplasma.
(3) Trypanosomidæ, with one flagellum, and an undulating membrane along the length of the body in some genera.
Family. Cercomonadidæ, Kent emend. Bütschli.
Small uniflagellate forms, without cytostome.
Genus. Cercomonas, Dujardin emend. Bütschli.
Oval or rounded organisms, with the aflagellar end often drawn out into a tail-like process.
Cercomonas hominis, Davaine, 1854.