Part 12 (2/2)

(Butschli '88; Maupas '83.)

The general form is oval, slightly compressed laterally with the dorsal side strongly arched. The ventral side is slightly incurved.

The anterior end is somewhat smaller than the posterior end, which is broadly rounded. The mouth is placed some distance from the anterior end in an oral depression and opens into a tubular oesophagus. There are usually two undulating membranes which do not extend beyond the mouth borders. The right undulating membrane extends down into the oesophagus and appears to be attached to the walls of the latter. The body stripes in front of the mouth are twisted to the left. The a.n.u.s is terminal and the contractile vacuole may be terminal or situated forwards in the dorsal region. The macronucleus is spherical and has one micronucleus attached. Food consists mainly of bacteria.

Movement rapid, but interrupted.

Fresh and salt water, common in infusions.

Colpidium colpoda Ehr., sp. Fig. 38.

Synonyms: _Colpidium cucullus_ Kent '81; _C. striatus_ Stokes '85; _Kolpoda cucullus_ Duj. '41; _Paramoecium colpoda_ Ehr. '38, Quennerstedt '67; _Plagyiopyla nasula_ Kent '81, G. & R. '86; _Glaucoma pyriformis_ G. & R. '86; _Tillina campyla_ Stokes '85, '88.

The body is oval, somewhat larger posteriorly, and a little compressed dorso-ventrally. The anterior end is twisted a little from the right to the left (more evident in fresh-water forms), and leans somewhat toward the ventral side. Under this portion, on the ventral side, lies the mouth in a large depression just above the middle of the body. The entire body is covered with uniform and delicate cilia, which are placed in longitudinal rows. These rows are almost straight on the dorsal side, but bend on the ventral surface, following the contour of the twisted anterior portion. The endoplasm is finely granular; the oesophagus leading into it is very distinct.

Schewiakoff ('89) describes two membranes, an inner and an outer; Maupas ('83) describes them as right and left. In the present species I was able to make out only one. The macronucleus is central, spherical in form, and bears a single minute micronucleus. The contractile vacuole is posterior and dorsal to the long axis of the body. The a.n.u.s is ventral to this axis and also posterior. Length 45, width 20. Common.

This marine variety is much smaller than the fresh-water form and the form differs in a number of respects, viz, in the anterior torsion and in the structure of the mouth. These may be, however, only individual variations of a widely spread species, and I believe it is perfectly safe to describe this as _Colpidium colpoda_.

[Ill.u.s.tration: Fig. 38.--_Colpidium colpoda_.]

Genus URONEMA Duj. '41.

(Quennerstedt '69; Cohn '66; Kent '81; Butschli '81; Schewiakoff '89; Shevyakov '96.)

Minute forms; colorless and constant in body form. The form is oval, slightly compressed on the ventral side, while the dorsal side is distinctly arched. The membrane is distinctly marked by rather widely separated striae. These occasionally have a spiral course about the body; in all cases they can be easily counted. The mouth is large and placed near the center of the ventral surface. It is sometimes approached by a very shallow depression or peristome from the anterior end, and marked by two rows of cilia. An undulating membrane extends down the mouth. Oesophagus absent. A long, stiff bristle extends outwards from the posterior end. The contractile vacuole is terminal or subterminal and near the a.n.a.l opening. The macronucleus is spherical, centrally placed, and with one micronucleus closely applied. Movement is rapid and usual forwards in a straight line, often found resting, however, with outstretched cilia in contact with some foreign body. Food mainly bacteria. Fresh and salt.w.a.ter, usually in decomposing vegetable substances.

Uronema marina Duj. Fig. 39.

Synonyms: _Enchelys triquetra_ Dujardin; _E. corrugata_ Duj.; _Cryptochilum griseolum_ Maupas '83; _Philaster digitiformis_ Fabre-Domergue '85.

Small animals with ellipsoidal form and about twice as long as broad. The mouth lies in the upper half of the body and bears a well-developed undulating membrane upon its left edge. The membrane is longitudinally striped and covered with long and vibratile cilia.

The right edge of the mouth bears cilia which are about the same in size as the body cilia, but are more closely inserted (Schewiakoff).

The most characteristic feature is the long caudal bristle, which is extremely delicate and about two-thirds the length of the body.

Schewiakoff thinks this bristle has a sensory function. I could not make this out, for although other protozoa ran against this bristle, often bending it well over to one side, the animal showed no sign of irritability but lay quiescent. A spherical macronucleus with attached micronucleus lies in the center of the body. The contractile vacuole is posterior in front of the bristle. The macronucleus was found to be double, as though just divided, in a large percentage of cases. This may be a precocious division of the nucleus long before signs of the body division are evident. Such a phenomenon, however, is rare, the macronucleus usually dividing at a late stage of cell division. Length 30 to 50; width 15 to 20. Common in decomposing algae.

[Ill.u.s.tration: FIG. 39.--_Uronema marina_.]

KEY TO MARINE GENERA OF PLEURONEMIDae.

Diagnostic characters: The mouth is at the end of a long peristome running along the ventral side; the body is dorso-ventrally or laterally compressed. The entire left edge of the peristome is provided with an undulating membrane which occasionally runs around the posterior end of the peristome to form a ”pocket” leading to the mouth. The right edge of the peristome is provided with a less-developed membrane. There may or may not be a well-developed pharynx.

Body small; not produced into Genus *_Pleuronema_ neck-like elongation

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