Conjugation in the Hypotrich Ciliate,Paraurostyla weissei (Stein): A Scanning Electron Microscope Study*

SYNOPSIS. Conjugation in Paraurostyla weissei has been investigated by scanning electron microscopy. In the course of conjugation, one member of each conjugating pair is resorbed. An organism that is being resorbed always lies to its partner's left and is always fused to its partner's oral region. A mechanism for the development of this asymmetry is proposed, based on the asymmetry of individual Paraurostyla. After resorption is complete, exconjugants enter a rounded, nonmotile stage which lasts several days. Exconjugants at this stage have been compared with cysts and have been found to be dissimilar.     

Doublet Formation and Cytoplasmic Symbionts in the Ciliate Urostyla grandis

The formation of homopolar doublets can be induced by the action of antibiotics which inhibit the growth of cytoplasmic bacterial symbionts whose cell cycle appears to be controlled by the host. They multiply during the macronuclear S-phase of the ciliate and become enclosed in vesicles and are largely destroyed just before cell division is completed. Since doublet formation is due to an incomplete cell division, and because experimental disturbances at the cell cortex of dividing ciliates also lead to doublets, the symbionts are thought to contribute some factor which is essential for normal cytokinesis of the host cell.     

Morphometric Variation in the Hypotrich Ciliate Genus Euplotes*†

SYNOPSIS. A quantitative method for the analysis of cirral patterns in the genus Euplotes is developed and contrasted with alternative approaches. Inherent variations in cirral pattern, as they are reflected in frequency distributions of intercirral distances, are ascertained through subclonal analyses of Euplotes harpa samples grown under different conditions. This assessment of the extent of variation within a form having 10 frontoventral cirri provides a basis for a comparative study of other Euplotes of cirrotype 10. These results suggest that all marine cirrotype 10 forms with a single dargyrome have the same configuration of frontoventral and transverse cirri. Similarly, most marine double dargyrome forms of cirrotype 10 have this same cirral pattern, and thus constitute variations upon the same morphometric theme.     

The Positioning of Ciliary Organelles in Hypotrich Ciliates*†

It is commonly observed in hypotrichs that new ciliary rudiments arise directly from or in close juxtaposition to certain pre-existing ciliary elements. Oral primordia often are initiated near specific cirri, cirral rudiments frequently arise as a result of the disaggregation of certain old cirri, and new dorsal ciliature is formed within pre-existing ciliary rows. In the first 2 situations it has been demonstrated experimentally that neither the old ciliature in question nor the specific cortical site marked by that ciliature is essential for the appearance of the new cirral rudiment. The experimental analysis done thus far suggests that the positions of oral and cirral primordia are determined by interacting gradients established in relation to certain reference points. The nature of the reference points is not fully elucidated; in some cases at least these points appear to be more closely related to topographic features of the cell than to specific pre-existing cortical structures. In the dorsal ciliary rows of Euplotes new ciliary units are formed usually and perhaps invariably in close proximity to old ones, and are generally oriented along the axis of the pre-existing row. The result is a tendency to perpetuate the preexisting row number across cell generations. Changes in row number, however, can occur as a result of occasional formation of new units at right angles to the row, a process that is much enhanced in certain homozygous segregants (basal body deficient). The optimal row number (stability range) as well as the number of ciliary units are under genic control. In addition, the spatial pattern of distribution of ciliary units among rows is invariant in all of the material examined. This pattern is presumed to result from an underlying field whose geometry is independent of both the number of units and the number of rows.     

Encystment in the Hypotrichous Ciliate Paraurostyla weissei: Ultrastructure and Cytochemistry1

The cyst wall of Paraurostyla weissei consists of four morphologically distinct layers. It shows an ultrastructure and composition similar to that of the previously described kinetosome-resorbing cysts, and its cytoplasm displays characteristics of “urostylid-type” cysts. Therefore it is possible to consider it a “transition ciliate” between Stichotrichina and Sporadotrichina.     

Participation of the Undulating Membrane in the Formation of Oral Replacement Primordia in Tetrahymena pyriformis*

SYNOPSIS. Cells of T. pyriformis GL-C, transferred from a complete axenic medium to a medium lacking amino acids, cease dividing after several hours, and instead begin to undergo oral replacement. This process can be synchronized by a single long 33.8 C treatment. Oral replacement was also observed during stationary phase of normal culture growth in cells of strain GL-C and WH-6 (syngen 1). In strain GL-C the oral replacement primordium is initiated by the appearance of a small number of kinetosomes adjacent to the anterior end of kinety 1, just posterior to the undulating membrane (UM). The UM then loses its cilia and becomes disorganized, and is thus converted into a field of kinetosomes which is broadest near its posterior end. This UM-derived field then becomes joined with the much smaller field which had appeared earlier near the anterior end of kinety 1. As a consequence, the right margin of the UM-derived field becomes continuous with the anterior end of kinety 1, and thus comes to appear as an anterior extension of this kinety. The membranelles and UM of the new oral area differentiate within this composite field. While this is going on, the membranelles of the old oral area are progressively resorbed; these old membranelles always remain spatially separate from the oral replacement primordium. In strain WH-6, the stomatogenic field initially formed adjacent to kinety 1 is substantial, and the role of the UM kinetosomes in stomatogenesis is less obvious than in strain GL-C. The posterior portion of the UM probably contributes to the oral replacement primordium, while the anterior portion is resorbed. In this strain small supernumerary primordia are occasionally seen adjacent to the portion of kinety 2 which is nearest to the posterior region of the UM. It is suggested that the junction between the posterior portion of the UM and the neighboring cortex can serve as an inductive zone for initiation of stomatogenesis, the UM itself having a varying capacity for direct provision of kinetosomes for the stomatogenic field. The flexibility of the stomatogenic site in T. pyriformis is discussed in relation to the apparent restriction of potentialities in peniculine ciliates such as Paramecium.     

Electron Microscopy of the Hypotrich Ciliate Oxytricha platystoma, with Consideration of its Macronuclear Organization

SYNOPSIS. The body of Oxytricha platystoma is covered with 2 membranes, the outer or pellicular membrane and the inner or cytoplasmic membrane. Each cirrus consists of a bundle of 25-50 cilia. There are 2 macronuclei and 2 micronuclei. The micronucleus is a very small body containing dense Feulgen-positive material. The macronucleus is an elongated body surrounded by a double membrane. The dense Feulgen-positive material is embedded in a less dense nucleoplasm. Some larger bodies found inside the nucleus may be nucleoli. There is a single reorganization band in each macronucleus. It consists of a solution plane and a reconstruction plane, and has a total thickness of 1.5 μ. The macronucleus divides amitotically, whereas the micronucleus divides mitotically.     

Epixenosomes: Peculiar Epibionts of the Hypotrich Ciliate Euplotidium Itoi Defend Their Host Against Predators

ABSTRACT. Euplotidium itoi harbors on its dorsal surface peculiar episymbionts (referred to as epixenosomes) equipped with a complex extrusive apparatus. In the laboratory. E. itoi stocks without epixenosomes behave and reproduce like symbiotized stocks. the hypothesis that epixenosomes play a defensive role against predators was tested by comparing the behavior of Litonotus lamella when preying upon Euplotes crassus, E. itoi without epixenosomes. and E. itoi with epixenosomes. Litonotus discharges its toxicysts upon direct-cell-to cell contact, and paralyzes the three types of prey with the same efficiency. Nevertheless, Litonotus can ingest Euplotes, Euplotidium without epixenosomes, and to a certain extent, Euplotidium with epixenosomes whose ejecting capability has been inhibited. while it never eats Euplotidium with unaltered epixenosomes. In each prey-type, about 60% of the individuals attacked by Litonotus toxicyst discharge are able to recover their normal behavior once transferred into pure sea water. This percentage for E. itoi with epixenosomes that are never eaten by the predator corresponds to the probability of survival. This probability is lower for the other two prey-types in which the prey engulfed by the predator do not have the chance to recover. These data support the hypothesis and suggest the involvement of the epixenosome's ejecting apparatus in a defensive function.     

Pleurotricha indica n. sp., a New Hypotrich Ciliate from the Indian Subcontinent1

A new species, Pleurotricha indica n. sp., is described, characterized by an average size of 220 × 119 μm, a firm and inflexible body, six rows of dorsal kineties, one left and two right rows of marginal cirri, and an “Oxytricha-like” pattern of ventral cirri. The parts of the macronucleus are variable in shape and number. The comparison with other members of the genus shows that P. indica differs from other congeneric species in the combination of these characters.     

Mucocysts in the Heterotrich Ciliate Spirostomum*

Mucus-like secretions by Spirostomum are demonstrated by a combination of anatomic and hydrodynamic technics whereby the presence of mucocysts and trails formed by their secretions can be shown. The mucocysts in this heterotrich differ somewhat in form and content from those reported for hymenostomes. It is suggested that the mucuslike secretions aid in lubrication when the ciliate swims near a solid boundary and reduce unsteady hydrodynamic effects when the organism swims in unobstructed fluid.     

New Methods for Cultivating,Harvesting, and Purifying Mass Cultures of the Hypotrich Ciliate Euplotes aediculatus1

A new method is described for mass cultivation of Euplotes aediculatus, a hypotrich ciliate containing omikron-symbionts. The ciliate cultures, continuously aerated in Erlenmeyer flasks (5000 ml) with 4500 ml medium, yield densities of 2300 cells/ml which are four to five times higher than cell densities of cultures grown in unaerated Fernbach flasks. Harvesting such cultures involves the application of 25-μm mesh sieves. Cells so concentrated can be purified by using columns or special chambers in which Euplotes migrates towards the cathodes in an electric field (field strength 7 V/cm).     

Regulation of Ciliary Pattern in Ciliates*

SYNOPSIS. The modes of pattern regulation found in the ciliates Dileptus and Paraurostyla are compared. These forms are systematically distant but both possess very extensive regenerative capacities. They are characterized by 2 types of ciliary patterns: the ciliature of Dileptus has largely a simple pattern composed of single kinetosomes while that of Paraurostyla has a complex pattern composed of aggregates of kinetosomes interconnected by amorphic matter. In both ciliates a change in cell size evokes pattern regulation which differs substantially in the extent of pattern replacement, timing, and localization of morphogenetic activities. It is concluded that these differences result from the pattern constituents.     

Pattern Formation in Mirror-Image Doublets of the Ciliate Stylonychia pustulata

ABSTRACT. Mirror-image symmetry doublets of the ciliate Stylonychia pustulata were obtained from the progenies of dividing cells in which cell division was inhibited by heat-shocks. In two components consisting of the doublet, the left (cell's) component possessed ciliary organelles arranged in almost the same pattern as in normal singlets, while the right one had surface organelles located in a mirror-image symmetry of those of the left component. In cell division of the doublet, two sets of ciliary primordia that were arranged in a mirror-image symmetry developed synchronously in both components. In about 80% of oral primordia (OP) of the right components, the arrangement of the membranellar bands became abnormal. In some cases, OP of the right component were occasionally separated into two longitudinal halves, each consisting of normal membranelles and inverted membranelles. A set of primordia of the paroral membranelles and fronto-ventro-transverse cirri was rarely derived from the basal bodies of the right half with a band of normal membranelles. As a result, a third component with the ciliary organelles normally arranged emerged on the right side of the original right component. The differentiation of membranelles and segmentation of the primordial streaks into cim proceeded from anterior to posterior. A cytoplasmic bulge with multiple right marginal cirral rows was frequently formed at the right margin of the doublet. The behavior in the separation of third and fourth streaks from a primordial streak of dorsal cirri was not mirror-image symmetrical in each component.     

Fission in Heteropolar Tandem Grafts of the Ciliate Stentor coeruleus*

SYNOPSIS Stentor pairs fused by their posterior ends show persisting mutual adhesion, tho they eventually pull apart. When immobilized in methyl cellulose these grafts constricted in 2 in the line of heal. In no other type of stentor graft has such deliberate separation been observed.