eden), and very contractile. The main feature of
importance in distinguishing it is the 4-part structure of the mouth
region, which, however, may not be obvious. Pharynx faint and smooth.
Contractile vacuole terminal. Macronucleus in one central body or in
numerous pieces scattered throughout the cell. Salt water.

Trachelocerca phoenicopterus Cohn '66. Fig. 30.

Synonyms: _T. sagitta_ Ehr. '40, Stein '59; _T. tenuicollis_
Quennerstedt '67, Kent '81; _T. minor_ Gruber '87, Shevyakov '96.

The body is extremely elongate and ribbon-like, and this, combined
with its wonderful power of extension and retraction, makes it one of
the most curious and interesting of microscopic forms. The anterior
end is square or cylindrical; the type species has a four-sided
mouth, but many specimens may be found which have a plain cylindrical
mouth region. One reason for this may be the fact that the extremity
gets broken off. In one instance I noticed a very large form with the
anterior end under some debris, which evidently held it tight, for
the body of the ciliate was thrashing back and forth and twisting
itself into knots, etc., like a nematode worm. Finally, the anterior
end broke off with about one-tenth of the body; the remainder, in an
hour, had regenerated a new anterior end with long cilia, but with
no indication of four sides. The small anterior piece was also very
lively, moving about and eating like the normal animal; its history,
however; was not followed. This species appears to be variable in
other ways as well; thus, in some cases the posterior end is rounded
(cf. Entz '84); in others it is pointed (cf. Kent '81, Cohn '66, et
al.).

Again, the macronucleus may be a single round body (Entz '84,
Buetschli '88) or in two parts (Kent '81), or in many parts scattered
about the body (Gruber). In the Woods Hole forms the tail is
distinctly pointed and turned back sharply, forming an angle at the
extremity. The cilia on this angular part are distinctly longer than
the rest. The function of this posterior part is apparently to anchor
the animal while it darts here and there upon the tail as a pivot,
contracting and expanding the while. The body is finely striated
with longitudinal markings; when contracted there are no transverse
markings nor annulations. The nucleus is in the form of many
fragments scattered throughout. Length of large specimen 1.7 mm.

[Illustration: Fig. 30.--_Trachelocerca phoenicopterus_.]

Genus