Genus LIONOTUS Wrzesniowski '70.

(Duj. '41; Wrzesniowski '69; Quennerstedt '65; '67; Cohn '66;Entz '84; Gourret & Roeser '88; Bütschli '88; Shevyakov '96.)

The body is flat and somewhat leaf-shape, flexible, and elastic. The anterior end is somewhat proboscis-like and flexible, but is not sharply demarcated as inLionotus. The central portion of the body is developed into a more or less arched dorsal mass, which usually contains the nuclei and contractile vacuoles. As a result of this local thickening, the body is surrounded by a thin hyaline margin. This, however, may be absent on the right side in some species. The mouth reaches from the anterior extremity to a short distance from the end, and usually approaches the left edge. An anus is present near the posterior end of the dorsal swelling. Trichocysts are numerous on the ventral surface, and often on the dorsal surface, where they are inclosed in minute papilla-like swellings. Cilia-distribution controverted. Maupas and Bütschli hold that ventral surface alone is ciliated; others (Kent and Dujardin) that cilia are uniformly distributed. The entire body, dorsal and ventral surfaces alike, are uniformly striated. The contractile vacuole lies posteriorly, on the right side and in the dorsal swelling. In the fresh-water formL. meleagris, it is connected with a long canal whose swellings are frequently taken for additional contractile vesicles (Bütschli); in the marine form described below the canal is not developed and a series of vacuoles takes its place; these are all contractile. The macronucleus may be single, double, quadruple, band-formed, or rosette-formed. Movement is steadily progressive and peculiarly gliding. Fresh and salt water.

Loxophyllum setigerumQuenn. '67.

Synonyms:Litosolenus armatusStokes '93;Litosolenus verrucosaStokes '93.

The body is flattened, irregular in outline, obtusely pointed anteriorly, the point being turned to the right; rounded posteriorly. The left edge is nearly straight, the right considerably arched with a few setæ on the posterior half. Contractile vacuoles are numerous, dorsal in position and on the right side. The macronueleus is beaded, the several spheres connected.

Varietyarmatum(Cl. & Lach.) Fig. 32.

Under the nameLitosolenus armatus, Stokes described a form from brackish water near New York, which should unquestionably be referred to the genusLoxophyllum, and I believe to Quennerstedt's speciessetigerum. While the latter possesses only a few setæ, the former has a number of them, and Stokes described his species as having a variable number. For this reason I include the Woods Hole form under the tentative namearmatum, as a variety of Quennerstedt'sL. setigerum. The flat margins are distinctly striated longitudinally, and faintly marked radially, on the dorsal surface. Longitudinal elevated striæ also run the length of the dorsal hump and upon the entire ventral surface. The ventral surface is alone ciliated. Upon the edges of the flat border are sharp-pointed, colorless, spine-like processes, situated at equal distances around the entire periphery except at the anterior end. Each spine is thick at the base and tapers to a full point which is curved upward—i. e., dorsally (fig. 32, a, b). The entire body is plastic and contractile, turning its leaf-like edge readily over objects upon which it creeps. The cilia are fine and uniform, with a tendency to lengthen in the oral region.

Length 100µ; greatest width assumed on contraction 85µ; when normal about 50µ.

Loxophyllum setigerum, var. armatum. a, b, c, ventral, dorsal, and lateral aspects.Fig. 32.—Loxophyllum setigerum, var.armatum.a, b, c, ventral, dorsal, and lateral aspects.ENLARGE

(Incorrectly calledLitonotusby many. Entz '84; Gruber '84;Bütschli '88; Kent '81; Schewiakoff '89; Shevyakov '96.)

The body is elongate and somewhat lance-shaped, widest at the central part and tapering to a point at the anterior end. The posterior end may be similarly tapered or rounded. The anterior end frequently proboscis-like, flat, and flexible, while the entire body is more or less elastic and contractile. The right side is flattened and alone provided with cilia, while the left side of the body proper is arched; on the left side of the proboscis is a row of coarse cilia resembling an adoral zone, and a row of trichocysts. A long peristome stretches down the thin, ventral side of the proboscis, and the mouth proper is situated at the junction of the proboscis and body; the mouth, as a rule, is invisible. The ciliated right side alone is striated in the majority of species. The contractile vacuole may be single or multiple, usually in the posterior region of the body and dorsal in position. The macronucleus is usually double, rarely single or quadruple, but may occasionally break into numerous smaller pieces. Movement, free-swimming or gliding, with especial tendency to get under clumps of foreign matter.

Fresh and salt water.

Lionotus fasciolaEhr. Fig. 33.

Synonyms.Amphileptus fasciolaEhr. '38; Dujardin '41; Lachmann '56; Cohn '66, Diesing '65.Loxophyllum fasciolaClaparède & Lachmann '58; Balbiani '61.Loxophyllum duplostriatumMaupas '83. Shevyakov '96.

Body frequently brown or brilliant yellow in color, somewhat sigmoid in form with tapering anterior end, the extremity of which is turned dorsally. The proboscis is about half the entire length and is not sharply marked from the rest of the body but tapers gradually, its base being equal to the diameter of the body at its middle point. The body is slightly contractile and the posterior end is carried to a rounded point, but not into a distinct tail. Unlike the fresh-water variety, this one has no hyaline margin nor hyaline caudal region, and the contractile vacuole is double or multiple on the dorsal side near the posterior end. Cilia are present only on the under (right) side, with, however, a row of large cilia marking the course of the elongate mouth, upon its left side. The right side is striated, the left arched and without markings. The endoplasm is finely granular with, however, larger food particles in the process of digestion, while specimens are occasionally seen with the natural form completely lost through distortion caused by over-large captures (Cf. also Wrzesniowski '70, p. XXIII, fig. 32). Movement continuous, slow, and gliding; very little tendency to jerking movements. Macronucleus double, both parts spherical, and placed in about the center of the larger part of the body; closely approximated but not, as Schewiakoff described, connected. In conjugation, a large form unites with a smaller one, the mouth parts being connected. Details of conjugation and macronuclei not made out. Length 200µ to 600µ.

Lionotus fasciolaFig. 33.—Lionotus fasciola.ENLARGE

Key to marine genera of Chlamydodontidæ.Diagnostic characters:Form usually ellipsoid, never very elongate. Transverse section of body circular or elliptical. The mouth is usually some distance from the anterior end and may be in the posterior part. Sometimes it is in the center of the ventral surface, again on the right side. The œsophagus invariably has a well-developed buccal armature, or a smooth peculiarly built œsophageal tube. Food particles of large size.1.Body cylindrical. Cilia about entire bodyGenus *NassulaBody flat22.a.Without a caudal process3b.With a caudal process53.a.Anterior end angular4b.Anterior end roundedGenusChlamydodon4.a.Dorsal striæ and cilia present, ventral cilia longerGenusOrthodonb.Dorsal striæ and cilia absent; posterior end not pointedGenus *Chilodonc.Dorsal striæ and cilia absent; posterior end pointedGenusScaphidiodon5.a.Caudal spine with posterior bristle-like cilia6b.Caudal spine without posterior bristle-like cilia; ventral cilia reducedGenusTrochilia6.a.With pigment spot on anterior angleGenusÆgyriab.Without such pigment spotGenusOnychodactylusc.Cilia on right edge only of greatly reduced ventral surfaceGenus *Dysteria* Presence at Woods Hole indicated by asterisk.

(Dujardin '41; Stein '67; Cienkowsky '55; Cohn '66; Clap. et Lach. '58;Kent '81; Maupas '83; Entz '84; Fabre-Domergue '88; Bütschli '88; Shevyakov '96.)

The body is ovoid or cylindrical, with well-rounded ends, and in some cases slightly flattened. The mouth is ventral and placed some distance from anterior end (1/4 to 1/3 total length). A slight depression on the ventral surface marks the mouth region, which is further indicated by larger and more powerful cilia. The rest of the body is uniformly ciliated. The entire body is marked by clearly defined spiral stripes. The mouth is circular and the œsophagus is supported by a considerable armature, which usually extends dorsally and to the left, rarely to the right. In some cases the structure of this armature is indistinct; again it can be clearly seen to consist of definite rods (Stäbchen). The anus is probably always terminal. Contractile vacuoles are variable in different species. In some cases there is but one, which is placed at the posterior end or centrally on the ventral side; in others there may be four—two dorsal and two ventral. In many cases trichocysts are uniformly distributed. Sometimes the body is colorless; again, and more often, it is brightly colored with red, blue, brown, or black pigment. The macronucleus is globular and central, occasionally band-form and with numerous attached micronuclei. Food substance varied, usually vegetable matter, see, however, below. Cysts are globular. Movement is a steady progression, combined with rolling.

Nassula microstomaCohn '66. Fig. 34.

Synonyms:Paramœcium microstomumCl. et Lach. '58, Gourret et Roeser '88;Isotricha microstomumKent '81.

Nassula microstomaFig. 34.—Nassula microstoma.ENLARGE

Body subcylindrical, rounded at each extremity, not quite twice as long as broad. A slight depression on one surface marks the position of the mouth, this depression being indicated by a row of longer cilia. The mouth is extremely small and is surrounded by a curious buccal armature. This is not made up of bars or rods, as in most species ofNassula, but appears perfectly smooth and uniform except for the considerable swelling at the inner end. The cuticle is firm and unyielding and marked by longitudinal and somewhat spiral rows of cilia and trichocysts. Under the microscope this is one of the most pleasing forms found at Woods Hole. Its color is yellowish brown from the presence of brilliant particles of coloring matter held in the cortical plasm, and, as it slowly rolls along, these particles and the black trichocysts give to the organism a peculiar sparkling effect. The macronucleus is almost central; the contractile vacuole posterior. The endoplasm appears well filled with food bodies, some of which could be distinguished asAmphidiniumandGlenodinium.

Length 55µ; greatest diameter 30µ.

(Dujardin '41; Engelmann '78; Stein '54, '58; Kent '81; Bütschli '88;Gruber '83; Cienkowsky '55; Möbius '88;Clap. et Lach '58; Wrzesniowksi '65; Shevyakov '96.)

Small forms, greatly flattened dorso-ventrally and almost egg-form in outline. The anterior end is bent distinctly to the left and forms a characteristic process, which, together with the entire margin of the body, is soft and flexible. The posterior end is, as a rule, broadly rounded. The ventral surface is finely striate, and this surface alone is ciliated. The lines of cilia converge at the mouth, and at this region the cilia are somewhat larger and more distinct, thus forming a functional adoral zone. The mouth is median and is situated in the anterior half of the body. It is surrounded by a well-defined armature, composed usually of from 10 to 16 rods. The contractile vacuoles are quite varied and from one to many in number, the number increasing with the size of the individual. The macronucleus is usually single, elliptical in form, and centrally placed; one micronucleus. Reddish granular pigment and trichocysts are occasionally present.

Chilodon cucullulusMüll., sp. Fig. 35.

Synonyms;Colpoda cucullusO. F. Müller;Loxodes cucullulus;Chilodon uncinatusEhr. '58, Perty '52, Dujardin '41;L. dentatusDuj., etc.

This extremely variable form has received so many different names that it hardly pays to enumerate them. It is one of the commonest and most widely spread ciliates known, although at Woods Hole I was surprised to see it so rarely. It is the type species of the genus and needs no further description. The specimens observed at Woods Hole had numerous contractile vacuoles and were 42 to 45µ long and from 28 to 32µ wide.

Chilodon cucullulusFig. 35.—Chilodon cucullulus.ENLARGE

(Cl. et Lach. '58; Entz '84; Möbius '88; Shevyakov '96.)

Small forms, firm in outline, and colorless or slightly colored. The body is somewhat clam-shaped, flattened, slightly curved or straight on the right side, the other more convex. The true ventral side is only a narrow strip along the right and anterior edge of the body, the apparent ventral side being a fold of the very large dorsal surface which comes around ventrally, forming a valved structure somewhat analogous to a clam shell. Cilia are limited to the outer edge of the small ventral surface, which also bears a peculiar spine at the posterior end. Behind this spine are larger cilia. The mouth opening lies in the anterior widened portion of the ventral surface and is connected with a smooth tubular pharynx. The right half of the dorsal side,i.e., the apparent dorsal side, is arched and bears longitudinal ridges. Two to four contractile vacuoles are placed on the ventral side. The macronucleus is usually dorsal, elliptical, and cleft, with one micronucleus attached. Fresh and salt water.

Dysteria lanceolataCl. et Lach. Fig. 36.

Synonym:Cypridium lanceolatumKent '81.

Dysteria lanceolataFig. 36.—Dysteria lanceolata.ENLARGE

Outline of the flattened body ovoid; body consists of two valve-like portions; the edge of the right valve is nearly straight, that of the left valve more or less sinuous; anteriorly it is cut away, obliquely and posteriorly it has a deep indentation in which the seizing spine rests. The cilia are confined to the ventral surface, here reaching, however, from the anterior dorsal extremity to below the posterior indentation. Posteriorly the cilia become larger, corresponding to the larger cirri ofD. armata, which are posterior to the spine. The mouth lies between the two valves and is surrounded by a long and smooth buccal armature which passes downward and backward to the left a distance equal to about half the entire body length. The macronucleus is situated in the dorsal region in the central part of the body. There are two contractile vacuoles, one behind the center of the buccal armature, the other near the inner end of this organ. Movement is in circles, the animal moving around quite rapidly when not attached by its posterior process. It is colorless and measures 45µ in length by 27µ in width. Claparède & Lachmann and Shevyakov describe it as 70µ long.

Key to marine genera of Chiliferidæ.Diagnostic characters:Mouth never lies behind the middle of the body; the œsophagus is but slightly developed. The undulating membranes are placed either on the edge of the mouth or in the œsophagus. A peristomial depression leading to the mouth is absent or very slightly indicated.1.Mouth in the anterior half, undulating membrane on left edge only; right edge continued in a long ventral furrowGenus *Frontonia2.Two undulating membranes; mouth central; no caudal bristlesGenus *Colpidium3.Two undulating membranes; caudal bristleGenus *Uronema* Presence at Woods Hole indicated by asterisk.

(Ehrenberg, subgenus ofBursaria'38; Claparède & Lachmann '58;Bütschli '88; Shevyakov '96.)

Form elongate and cylindrical, or often flattened dorso-ventrally, with round or pointed ends. It is usually plastic and contractile. Cilia are evenly distributed about the body and are similar in length. The large, open mouth lies on the anterior half of the ventral surface, and is elongate and oval in outline. On its left edge is a well-defined membrane which stretches across to the right side of the mouth. On the right edge is a small, longitudinally striped tract which is free from trichocysts and smooth in appearance. This tract is continued posteriorly in a long furrow, which in some cases reaches the posterior end of the animal. A few rows of cilia in this furrow vibrate differently from the others and give the effect of a membrane (Bütschli). The œsophagus is extremely short and hard to make out. The body is usually covered uniformly with trichocysts, often of considerable size. There are 1 or 2 vacuoles with long canals radiating throughout the endoplasm. The macronucleus is oval and centrally placed. Micronuclei vary from one to many. An anal opening is placed at the end of the long ventral furrow. The plasm is colorless or green by the presence of Zoochlorella, or colored brown or black by pigments. In these cases there is a considerable pigment mass on the anterior end. Movement is regular, forward, and combined with rotation. Food consists of foreign objects, diatoms, other protozoa and the like. Fresh and salt water.

Frontonia leucasEhr. Fig. 37.

Synonyms:Frontonia vernalisEhr. '38;Bursaria leucasAllman '55, Carter '56;Panophrys leucasDuj. '41, Stein '67;Panophrys vernalisDujardin '41, Stein '67;P. chrysalisDuj. '41, Fromentel '74;Cyrtostomum leucasStein '67, Kent '81.

Frontonia leucasFig. 37.—Frontonia leucas.ENLARGE

Form ovoid, elongate, occasionally a little flattened dorso-ventrally. Mouth in the anterior third of the body. The left edge of the mouth carries a distinct undulating membrane; the right edge is plain, longitudinally striated and bears cilia. It is slightly depressed and the depression is carried posteriorly in the form of a shallow furrow which reaches to the posterior end. The contractile vacuole is on the left side, the spheroidal nucleus on the right side of the furrow. The body is uniformly covered with fine cilia, and the periphery is uniformly studded with large trichocysts, except along the furrow. Food consists of dinoflagellates and other small forms. Color dark brown to black.

Length 330µ; width 200µ.

This form differs considerably from the fresh-waterFrontonia leucasas described by Schewiakoff '89, especially in the extreme length of the peristomial furrow, in the position of the nucleus and contractile vacuole, and in the nature of the water canals. These in the Woods Hole form are very irregular in size and very much branched, not uniform as in Lieberkühn's (see Bütschli) figure ofFrontonia leucas, nor radiating as in Schewiakoff's description. This may be the same species asFrontonia marina, of Fabre-Domergue '91, whose description and figure I have not seen.

(Bütschli '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 œsophagus. There are usually two undulating membranes which do not extend beyond the mouth borders. The right undulating membrane extends down into the œsophagus 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 anus 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 colpodaEhr., sp. Fig. 38.

Synonyms:Colpidium cucullusKent '81;C. striatusStokes '85;Kolpoda cucullusDuj. '41;Paramœcium colpodaEhr. '38, Quennerstedt '67;Plagyiopyla nasulaKent '81, G. & R. '86;Glaucoma pyriformisG. & R. '86;Tillina campylaStokes '85, '88.

Colpidium colpodaFig. 38.—Colpidium colpoda.ENLARGE

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 œsophagus 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 anus is ventral to this axis and also posterior. Length 45µ, width 20µ. 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 asColpidium colpoda.

(Quennerstedt '69; Cohn '66; Kent '81; Bütschli '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 striæ. 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 anal 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 saltwater, usually in decomposing vegetable substances.

Uronema marinaDuj. Fig. 39.

Synonyms:Enchelys triquetraDujardin;E. corrugataDuj.;Cryptochilum griseolumMaupas '83;Philaster digitiformisFabre-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 50µ; width 15 to 20µ. Common in decomposing algæ.

Uronema marinaFig. 39.—Uronema marina.ENLARGE

Key to marine genera of Pleuronemidæ.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 neck-like elongationGenus *PleuronemaBody medium-sized; anterior end produced into neck-like elongationGenus *Lembus* Presence at Woods Hole indicated by asterisk.

(Perty '52; Clap. & Lach. '58; Stein '59, vol. I; Quennerstedt '67;Kent '81; Bütschli '88; Schewiakoff '89; Shevyakov '96.)

Small to medium-sized ciliates, with an unchanging form. They are somewhat lens-shape and laterally compressed, the two surfaces about equally arched. The ventral surface is nearly straight or but slightly arched; the dorsal is quite convex. The anterior and posterior extremities are equally rounded. The peristome begins as a small depression, but becomes larger until it takes in nearly all of the ventral surface. The depression becomes much deeper at about the center of the body, and is especially marked on the left side of the peristome. In this deeper portion is the mouth, with an almost imperceptible œsophagus. Upon the left edge of the peristome is a high, undulating membrane, sail-like in appearance when extended. This may stretch around the posterior edge of the peristome and upon the right aide, thus forming a pocket by means of which the food particles are directed into the mouth. The rest of the right edge of the peristome is occupied by closely approximated powerful cilia (Bütschli) or a second undulating membrane (Stein). The body cilia are relatively long. Trichocysts and caudal bristles may be present. The contractile vacuole is subterminal and dorsal; it is questionable whether there are canals leading to it. A round macronucleus with one micronucleus is in the anterior half of the body. The anus is terminal. Food is chiefly bacteria. Movement combines springing with swimming and rotation. Fresh and salt water.

Pleuronema chrysalisEhr., sp. Fig. 40.

Synonyms:Pleuronema crassaDujardin '41;P. marinaDuj. '41; Fabre-Domergue '85;P. coronataKent '81;Paramœcium chrysalisEhr. '38;Lembadion oraleG. & R. '88;Histiobalantium agileStokes '85, '88.

The body is ovoid, slightly flattened, rounded at both ends, the anterior end sharper than the posterior. The ventral surface is almost entirely taken up by a peristome which extends from the anterior end posteriorly three-quarters of the body length. The posterior end of the peristome is straight, the left curved, following the depressed portion. The body is covered with fine cilia in longitudinal lines, except on the peristome. The mouth is small and situated in the hollow of the peristome near the left border. On the left peristome edge is a large undulating membrane. It begins near the anterior end of the body and increases in height posteriorly following the peristome edge around on the right side. This posterior bend of the membrane causes the appearance of a full sail, so often seen. It can be entirely withdrawn and folded together in the peristome. On the right edge of the peristome are large, powerful cilia. The contractile vacuole is central and dorsal; the macronucleus is in the anterior half of the body, with one attached micronucleus. Food consists of bacteria. Not very common. Fresh and salt water. It often remains quiet, with membrane and cilia outstretched, as though dead, but suddenly gives a spring and is gone.

Pleuronema chrysalisFig. 40.—Pleuronema chrysalis.ENLARGE

Pleuronema setigera, n. sp. Fig. 41.

Body colorless, elongate, and with the general form of a cucumber, the posterior end being somewhat pointed. The mouth and relatively small peristome are situated in the lower third of the body. The peristome begins as a shallow furrow at the center of the ventral surface and dips sharply into the buccal depression, which is deep and turned toward the posterior end. The left edge of the peristome bears a high undulating membrane, which extends anteriorly only as far as the center of the body; posteriorly it passes around to the right edge of the peristome, thus forming the characteristic membranous pocket. Inside the oral depression is a second undulating membrane, running down to the mouth. This is small and without an œsophagus. The body is clothed with long setose cilia which are frequently fully outstretched when the animal is resting, a slight tremor of the large membrane alone indicating vitality. Posteriorly these appendages are drawn out into long filiform setæ, the number varying in different individuals from three to nine or ten. These are extremely fine and difficult to see without a high power (e.g.1/12 oil) and careful focussing of the substage condensor. LikeP. chrysalis, the resting periods are terminated by sudden springs, otherwise the movements are steady and forward. The macronucleus is central, and the contractile vacuole posterior and terminal. Length 45µ to 50µ; greatest diameter 17µ. In decaying algæ.

It was this form, I believe, that Peck '95 described as a "ciliate."

Pleuronema setigeraFig. 41.—Pleuronema setigera.ENLARGE

Back to Index Next