contractile vacuole lies on the right side in the region of the
anal cirri, sometimes just above them, sometimes below. The anus is
posterior and on the right side. The characteristic macronucleus is
long and band-form, its main portion being usually on the left side
with an anterior and a posterior arm toward the right. Movement is
rapid swimming, which, however, is frequently broken by creeping
periods, during which the animals appear to be examining the foreign
body on which they creep.

Fresh and salt water.

Euplotes charon Ehr. Fig. 52.

Synonyms: _Trichoda charon_ Mueller; _Ploesconia charon_; _P.
affinis_, _subrotunda_, _radiosa_, _longiremis_, Dujardin '41.

The body is oval, small, and somewhat variable in length. The
carapace is strongly marked upon the dorsal side by deep longitudinal
grooves, 6 to 8 in number; the grooves may be absent, however. The
adoral zone extends to the posterior third of the body, the mouth
and oesophagus are directed anteriorly. There are 10 ventral cirri,
7 of which are on or near the frontal border and 3 near the right
edge. There are 5 posterior cirri and 4 anal cirri, of much smaller
size. The cirri may or may not be fimbriated, the latter condition
indicating the approaching disintegration of the body and is
abnormal. The macronucleus is long and band-formed or horseshoe
shape. The contractile vacuole lies on the right side dorsal to the
posterior cirri.

Fresh and salt water. Length 45 mu; diameter 25 mu.

[Illustration: Fig. 52.--_Euplotes charon_, dorsal and ventral
aspects.]

Euplotes harpa Stein. Fig. 53.

The body is elongate, oval, somewhat widened anteriorly, and has
rounded ends. The frontal margin is three-toothed. Ten ventral cirri.
Dorsal surface provided with 8 longitudinal markings. The peristome
is long and broad, with considerable variation. The adoral zone
consists of powerful membranelles arranged in a continuous curve
from the mouth to the extreme right frontal margin. Seven of the 10
ventral cirri are situated at the anterior extremity; the remainder
are arranged in a triangle on the right edge. The anal cirri, 5 in
number, are long and stiff; the marginal cirri smaller and finer. The
nucleus and contractile vacuole are similar to those of the preceding
species.

Length 95 mu; width 54 mu.

[Illustration: Fig. 53.--_Euplotes harpa_.]

Genus DIOPHRYS Dujardin '41.

(Buetschli '88.)

Medium size, colorless to yellow, rigid in f