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This paper illustrates the structural diversity of the ciliary membrane of the somatic ciliature in 68 ciliate genera and describes the interior architecture of several presumptive sensory cilia. Freeze-fracture technique reveals a variety of intramembrane particle arrays known as ciliary necklace, ciliary plaques, and ciliary rosettes. While the function of these arrays is still largely unknown, their distribution among ciliates suggests a phylogenetic correlation. Whereas current systems of ciliate classification are primarily based on the character of the ciliature which surrounds the cytostome as well as on the morphogenesis of this oral ciliature, the data presented in this paper are well suited to emphasize the significance of the somatic ciliature for the reconstruction of ciliate phylogeny. This is particularly evident when the freeze-fracture data are mapped in parallel with a simplified phylogenetic tree based on the appearance of both the oral and the somatic ciliature. The freeze-fracture data are in agreement with hypothesis of a non-hymenostome origin of the spirotrichs and suggest a close relationship with respect to the origin of the Hymenostomatida from the Colpodida instead of from the Nassulida. The presumptive sensory cilia show a significantly greater particle density than most somatic cilia. While the particles may represent receptor proteins or ion channels, with the freeze-fracture technique it is at present impossible to specify the modalities of such "sensory" cilia.

Host-parasite relationships have been studied by electron microscopy using glutaraldehyde-OsO4-fixed pellets of lymphoid cultures infected in vitro by Theileria annulata and T. parva. Intracellular presence of the parasite resulted in a progressive and marked lymphoblastoid transformation. The schizont stage periodically provoked the formation of, and adopted an intimate association with, cytoplasmic annulate lamellae in the interphase cell. Annulate lamellae developed from the outer nuclear membrane of the host cell by a delamination process and were taken into the cytoplasmic matrix of the schizont by phagotrophy through the cytostome. Schizont nuclei themselves were seen to divide at the prometaphase stage of host cell mitosis, the division being characterized by the development of intranuclear spindle microtubules anchored in spindle pole bodies. A hypothesis is propounded that Theileria parasites, consequent on interiorization, provoke the blastoid transformation and the formation of annulate lamellae through the influence of components of their genomic material on host cell deoxyribonucleic acid (DNA) and that the annulate lamellae represent a species of messenger ribonucleic acid (mRNA) and serve as a monitoring device for the schizont, facilitating the accurate timing of the host cell cyclical events.

The survival or degeneration of nuclei produced after meiosis in Paramecium caudatum depends upon their position in the cytoplasm. The surviving nucleus lies in the paroral region, which is the region around the cytostome. In this study, this was confirmed by quantitative measurements of the location of surviving nuclei in both stained and living conjugating cells. Observation of nuclear behaviour in living cells shows that there is an active mechanism for localizing one of the four meiotic products into the paroral region after the second meiotic division. When this mechanism is inhibited by vinblastine, none of the four nuclei gets into the paroral region and all of them become pycnotic, before degenerating. The results show that migration into the paroral region is essential for survival of the nucleus and that microtubules are involved in this nuclear migration.

SYNOPSIS. Spathidium spathula irradiated with 0 to 55 kr of × rays showed one or more of the following kinds of behavior: (1) Death of an undivided cell (primary death); (2) death of a descendant of an irradiated cell (secondary death); (3) permanent injury including one or more of the following: low daily division rate, excessive macronuclear enlargement, total loss of micronuclei, cytostome replication, heavy pigmentation, and decreased motility; (4) temporary division retardation for 1 to 2 days followed by apparent complete recovery; and (5) no apparent injury. The first 3 kinds of behavior increased with increasing dosage from 15 to 25 to 55 kr. At 6 kr only the last 2 categories were observed. The LD50 for 8 days was 46 kr for both primary and secondary death, or 60 kr for primary death alone. Micronuclear number varied greatly following irradiation in lines showing either permanent or temporary injury. Two different responses occurred: (1) The micronuclear number averaged about twice the normal number of 20 with a large range (0 to 360) 1 day after exposure. The number gradually decreased during the next 2 days; (2) some cells lost all micronuclei following irradiation, the incidence increasing with dose. At 55 kr complete loss of micronuclei occurred in 96% of the surviving lines.

SYNOPSIS. The fine structure of 2 isolates of Trypanosoma congolense maintained in laboratory rodents has been studied from thin sections of osmium- and aldehyde-fixed flagellates. The pellicular complex, nucleus, and flagellar apparatus are all similar to those of other African trypanosomes. Aberrant intracellular differentiation of the flagellum is occasionally found. As in bloodstream forms of other salivarian trypanosomes the single mitochondrion forms an irregular canal running from one end of the body to the other, with a shallow bowl-shaped expansion forming a capsule for the fibrous kinetoplast (mitochondrial DNA). A connexion between the mitochondrial envelope of the kinetoplast and the basal body of the flagellum is not evident, and sometimes the flagellum base is not even apposed to the kinetoplast but lies behind it. Tubular cristae are present in the mitochondrial canal and, by light microscopy, this structure gives a positive reaction for NAD diaphorase suggesting at least some activity in electron transport, even tho at this stage in its life cycle respiration is doubtfully sensitive to cyanide and cytochrome pigments are in all probability absent. The region of the cytoplasm between the nucleus and the flagellar pocket has all the trappings associated with secretory cells in higher animals, or with the secretion of surface structures in phytoflagellates. just behind the nucleus a limb of granular reticulum subtends a Colgi stack of flattened saccules with attendant vesicles. Close to the distal pole of the Golgi complex is a network of smooth-membraned cisternae, termed here the agranular or secretory reticulum, which undergoes localized swelling with the accumulation of a secretory product to form large spherical sacs or vacuoles. These network-linked vacuoles probably correspond to the post nuclear vacuole complex visible by light microscopy. From its apparent secretory function this complex is regarded here as being possibly an extension or derivative of the Golgi complex, the smooth-membraned tubules lying alongside the 2 structures possibly representing a link between them. By analogy with phytoflagellates and the secretory cells of higher animals, it is suggested that the secretion is transported for discharge into the flagellar pocket by way of multivesicular bodies and smooth-walled tubules or vesicles. Spiny pits in the wall of the flagellar pocket, and similar-sized vesicles in the nearby cytoplasm, could be stages in either exocytosis of secretion or endocytosis (pinocytosis). It is tentatively suggested that the secretion may be the material from which the surface coat is formed. Neither a cytostome nor a contractile vacuole has been observed in T. congolense.

SYNOPSIS. In the culture forms of the elasmobranch trypanosome Trypanosoma raiae is found a prominent cytopharyngeal complex. This consists of a group of 5 or 6 microtubules associated with a deep invagination of the cell membrane which arises from a cytostome near the opening of the flagellar pocket. This structure is a constant feature of the various epimastigote and trypomastigote forms that this flagellate has in culture. Replication of the cytopharyngeal apparatus is completed before cytokinesis. Experiments using ferritin as an electron dense tracer show that endocytosis occurs from the blind ending of the cytopharynx both in the exponential and stationary phases of growth in vitro. Ferritin is transported from the cytopharynx by endocytotic vesicles to large, membrane-bound vacuoles in the posterior region of the cell. Ultrastructural location of non-specific acid phosphatase within these digestive vacuoles and also within the Golgi apparatus is reported. Coated vesicles found in association with the flagellar pocket are another route of uptake of ferritin by T. raiae.

The Feulgen-positive kinetoplast of Bodo sp. resembles the kinetoplasts of trypanosomes in ultrastructure. In direct continuity with it is a single, long, sinuous mitochondrion that encircles the body completely. Near the anterior depression from which the two flagella emerge is an apical cup, possibly serving as a cytostome, from which a deep open channel descends into the cell. Its cavity is lined by a membrane and surrounded by fibers that in appearance and number resemble the fibers of a flagellum, and that originate with the flagellar basal bodies near the kinetoplast.

The localization of induced and constitutive acid phosphatase activity in Euglena was studied by light and electron microscopy, using two different cytochemical methods. Cells grown in high phosphate medium have constitutive acid phosphatase activity in three regions: in the Golgi complex, around the paramylum bodies, and in the peri-reservoir vesicles. Cells that have formed an induced acid phosphatase by exposure to a phosphate-deficient medium have, in addition to the constitutive activity localized exactly as in the uninduced cell, a strong activity in the pellicle. The induced activity is not uniformly distributed over the pellicle, but is localized at the notch of each pellicle complex, near a group of about four fibrils and near a characteristic vesicle of the endoplasmic reticulum. In the cytostome, where fission begins during division, there is an alternation of large and small pellicle complexes, both of which have induced phosphatase activity. A similar alternation is seen over the entire pellicle of dividing cells.

Trichomonas tenax(T. tenax) and Trichomonas hominis (T. hominis) were collected, cultured and sampled for comparative microscopical studies using electron microscope. 1. Both flagellates were oval in shape and surrounded by a distinct outer membrane. Five recurrent flagella and one anterior flagellum had, each, 9 paris of peripheral and 1 pair of central fibrils, Undulating membrane was curved over the recurrent flagella, and bended in the middle at right angles with cell surface. Cytostome, engulfing bacteria, was observed in T. hominis. 2. In the cytoplasm, there were fine dense glycogen particles, and vacuoles containing ingested materials. Dense pigment rods were also observed in both flagellates, but the rods were not distributed around the vacuoles in T. hominis. 3. In T. tenax axostyle appeared as a cup-shaped structure comprising a single row of 41 fibrils, each about 120 a in diameter. It enclosed glycogen particles, and the open side was faced to the nucleus. 4. Endoplasmic reticulum was observed around the nucleus, but it was less developed in T. hominis. 5. Nucleus was ovoid having double nuclear membrane, which was clearly defined in T. hominis. 6. Blepharoplast, parabasal body, Golgi appartus and mitochondrion was not observed in both flagellates.

SYNOPSIS. The first sign of merozoite formation in schizonts of Haemoproteus columbae is the accumulation of dense material at intervals beneath the plasma membrane of the schizont. The schizont's membrane then invaginates in deep furrows cleaving the parasite into pseudo-cytomeres. thereby increasing the area of membrane available for differentiation. Signs of differentiation appear under this membrane as soon as it is formed. Rhoptries and polar rings develop in the region of the dense accumulations, the cytoplasm containing these structures begins to elevate, and each evagination differentiates into a merozoite. When the merozoite is half-formed, the cytostome appears, then dense bodies at the apex of the organism, and finally a spherical body intimately associated with a mitochondrion. These merozoites of Haemoproteus are assumed to be the forms that penetrate erythrocytes and become gametocytes. They contain the same organelles as merozoites of Plasmodium. However, the merozoites of Haemoproteus are oval like the erythrocytic merozoites of Plasmodium rather than elongate like the exoerythrocytic merozoites. This body shape may be a generic characteristic or it may indicate a structural difference between exoerythrocytic merozoites and merozoites that infect erythrocytes. When the merozoites of Plasmodium, Haemoproteus and Leucocytozoon are compared, the first 2 genera appear closely related, but Leucocytozoon seems very different. Perhaps it should not be included within the Haemoproteidae.

Evidence is presented for the passage of bacterial food organisms into a cytoplasmic tube present in Cyathomonas truncata . The tube thus appears to function as a gullet or cytostome. A fringe, which may assist in feeding, surrounds the entrance to the gullet. Microtrichocysts and macrotrichocysts are recognized in this organism. The undischarged trichocysts bear a strong resemblance to retractile bodies of kappa particles, and are able to incorporate 3 H-thymidine. The trichocysts of Cyathomonas can thus be classified with that ever increasing category of cytoplasmic organelles whose ultrastructural and molecular properties suggest that they are a type of endosymbiont.

SYNOPSIS. An electron microscope study of Plasmodium coatneyi in the rhesus monkey supplied information on the fine structure of trophozoites, gametocytes and of the host cell. The trophozoites resemble other mammalian malaria parasites. They do not have typical protozoan mitochondria, but instead a concentric double-membraned organelle, which, it is assumed, performs mitochondrial functions. They feed on the host cell by pinocytosis, engulfing droplets of erythrocytes thru invaginations of the plasma membranes at any region of the cell or thru the cytostome. Digestion of hemoglobin takes place in small vesicles pinched off from the food vacuole proper. Gametocytes can be clearly distinguished into macro- and microgametocytes. Macrogametocytes are covered by 2 plasma membranes, the inner one appearing thicker in some places. The cytoplasm is filled with Palade's particles and has numerous vesicles of endoplasmic reticulum and toxonemes. In microgametocytes most of the inner membrane is thickened, the cytoplasm has few Palade's particles and vesicles of the endoplasmic reticulum and does not have toxonemes. Erythrocytes with trophozoites are irregularly scallop-shaped and have elevated points with knob-like protrusions covered by a double membrane. If these protrusions are sticky they might be in part responsible for clumping and arresting the schizonts and segmenters in the capillaries. The host cell contains numerous Maurer's clefts which in some instances are continuous with the membranes of the parasite suggesting that they might originate from them.

The trophozoite stages of P. chabaudi and P. vinckei are polymorphic. The single plasma membrane that surrounds the young trophozoite encompasses a cytoplasm that contains abundant polyribosomes, pigment, granular endoplasmic reticulum, and pinocytotic vesicles. Its nucleus, irregular in shape, with unremarkable nucleoplasm, is delimited by a fenestrated nuclear envelope. As the trophozoite matures, there is a reduction in the number of pinocytotic vesicles, and the cytostome becomes active. Likewise, condensation appears beneath the plasmalemma of the parasite. These condensations develop into a dilaminate plaque, which ultimately contributes to the triple-layered pellicle of the merozoite. Concurrent with the changes in the young schizont, an apparatus that consists of microtubules and is similar in structure to a mitotic spindle can be found within the intact nucleus. The mature schizont presents a highly lobulated outline. The pellicle of the budding merozoite is trilaminar. The outer lamina is derived from the plasma membrane of the schizont, the middle and inner laminae from the dilaminate plaque. Two mechanisms of merozoite formation are described.

Plasmodium elongatum, an avian malarial parasite, differs from other such parasites by infecting both the circulating red blood cells and the hematopoietic cells. The exoerythrocytic development of P. elongatum occurs mainly in these red cell precursors. The fine structure of the asexual stages of P. elongatum has been studied in the bone marrow and peripheral blood of canaries and compared with that of the asexual stages of other avian malarial parasites. With minor differences, the merozoites of P. elongatum possess the same organelles as those in the exoerythrocytic merozoites of P. fallax and the erythrocytic stages of P. cathemerium, P. lophurae, P. fallax, and P. gallinaceum. The developmental sequence is also essentially similar to that of other avian malarial parasites, in that upon entry into a new host cell, the dedifferentiation, growth, and redifferentiation phases take place. However, we have found some important differences in the feeding mechanism of P. elongatum. The cytostome is involved in the ingestion of host cell cytoplasm in both exoerythrocytic and erythrocytic stages, in contrast to P. fallax, in which the cytostome is inactive in the exoerythrocytic stages. In P. elongatum, host cell cytoplasm is ingested through the cytostome, and "boluses" are formed and incorporated into a large digestive vacuole. Subsequently, the digestion of the boluses takes place in this digestive vacuole. Thus, in regard to the function of the cytostome, the exoerythrocytic stages of P. elongatum appear to be closely related to the erythrocytic stage which has a feeding mechanism similar to that of the erythrocytic stage of other avian malarial parasites.

SYNOPSIS. Thin sections of the following stages of Trypanosoma avium were examined in the electron microscope: Trypomastigote forms from the blood of a bird, large epimastigote forms developing from the former after 2 hours in vitro, small epimastigote and metacyclic trypomastigote forms developing after longer periods of cultivation in vitro. The general structure of all stages was similar to that which is already well known for the genus, with the following points being of particular interest: (1) In the large trypomastigote and epimastigote forms, and possibly also in the smaller forms, the flagellar sheath was attached to the pellicle, at least in places. In the large trypomastigote forms, this resulted in the drawing out of a “fin” or ridge of cytoplasm, particularly in the mid-region of the body, to form a true undulating membrane. (2) At least some of the individuals in the blood of a bird have 2 basal bodies, one of which is aflagellate, altho these individuals rarely if ever divide. The large epimastigote forms into which they transform in vitro develop 4 basal bodies (2 flagellate and 2 aflagellate) before dividing. (3) The chondriome is well-developed in all stages, extending thruout the body, even to the tip of the elongated posterior end of the form in the avian host. (4) A short cytostome, leading from the flagellar pocket, was seen in the hematozoic (blood-inhabiting) trypomastigote form but not in other stages. (5) It is suggested that the forward movement of the kinetoplast and basal body during the transformation from trypomastigote to epimastigote form is mediated by localized cytoplasmic movement, resulting in the “rolling-up” of the organism's hind end. It is further suggested that protein synthesis is reduced or even suppressed entirely in the small epi- and trypomastigote forms appearing at the end of the developmental cycle in vitro or in the insect host, such synthesis recommencing rapidly after re-entry into the vertebrate.

Trichomonas vaginalis Donne, 1837 can be made resistant to a variety of chemical compounds and is a suitable organism for the study of resistance, particularly as it can be maintained indefinitely in bacteria-free cultures. Moreover, it possesses a cytostome and ingests relatively large granules (for example, rice starch), and probably acquired resistance in the case of this flagellate does not depend on non-transit of a particular compound through the surface membrane as is apparently the case in resistant trypanosomes. Thus a strain of T. vaginalis was made resistant to 4.4′-diamidino stilbene. Initially the strain tolerated not more than 1 in 70,000; but by culturing repeatedly on gradually increasing concentrations, a strain was obtained which grew in a concentration of 1 in 5,000. 4.4′-Diamidino stilbene fluoresces in ultra-violet light, and it was easy to demonstrate its presence in the cytoplasm of resistant flagellates grown on a concentration of 1 in 5,0001. On the other hand, we failed to make an Indian strain of Leishmania donovani and a Sudan strain of L. infantum resistant to this drug by the usual method of sub-culturing in gradually increasing concentrations.

SUMMARYAn automated suspension culture system for the cultivation of Plasmodium falciparum is described which retains a degree of flexibility which is absent in other automated culture apparatuses. Not only does this system of cultivation promote rapid multiplication of asexual parasites but also permits the development and maturation of gametocytes. Using a combination of gelatin flotation and N-acetyl glucosamine treatment synchronous development of gametocytes was achieved. The total time for gametocyte maturation in vitro under the conditions provided was 7 days. Stages II and V required 48 h for development whilst I, III and IV needed 24 h each. Mature microgametocytes were relatively long lived in comparison with macrogametocytes. Electron microscopic study of the synchronized stages confirmed the observations of Sinden (1982) but, in addition, we noted the presence of Garnham bodies, a cytostome in all stages and dense spherules in stages I–III similar to the fenestrated buttons in sporozoites and exoerythrocytic forms. The relationship between the number of osmiophilic bodies in the mature gametocytes and their ability to escape from the red cell is reaffirmed.

Summary It has been known for many years that trypanosomatids require exogenous essential growth factors in order to divide. Two surface domains are involved in starting nutrient endocytosis: the flagellar pocket and the cytostome. Although the flagellar pocket plays a fundamental role in the endocytic process occurring in several trypanosomatids, we have shown the cytostome as the main structure involved in this process in epimastigote forms of T. cruzi. After one minute of endocytosis, cargo is still found at the cytostome entry as well as along the cytopharynx. After two, five and fifteen minutes of endocytosis, cargo was seen inside vesicles and tubules, prior to fusing with reservosomes. Three-dimensional reconstruction of these tubules and vesicles showed they are interconnected, forming an intricate and branched network, distributed from the perinuclear region to the posterior end of the cell. Whole unfixed parasites that had taken up gold-protein conjugates for fifteen minutes were washed and dried on electron microscope grids. Observation with an energy-filtering transmission electron microscope revealed long gold-filled tubules at the posterior end of the cell. Parasites treated with ammonium chloride had their intracellular traffic slowed down, which allowed us to observe many events of vesicle fusion. The acidic nature of this network was evidenced using acridine orange. Based on pH and protein uptake kinetics we propose that the vesicular-tubular network is the early endosome of Trypanosoma cruzi epimastigotes.

The surface structure of the ciliary zone in 13 species of ciliates found in the large intestine of the horse was observed by scanning electron microscopy. In Holophryoides ovalis many fine depressions considered to be a result of phagocytosis or pinocytosis in the naked cytostome were noticed. In Blepharocorys spp. a distinct section was present between the portion with cilia and that without cilia. It was not present, however, in some species of the family Buetschliidae, such as Bundleia postciliata and Didesmis spp. The species of Entodiniomorphida had a lip around the ciliary zone with cilia forming synciliary tufts. In Spirodinium equi and Tetratoxum unifasciculatum the ciliary zone revolved counter-clockwise in an en face view. Some differences in the surface structure of the ciliary zone between the entodiniomorphid and spirotrich ciliates are discussed.

SLEIGH, M. A. & BARLOW, D. 1976. Collection of food by Vorticella. Trans. Amer. Micros. Soc., 95: 482-486. Two bands of cilia act together in feeding by Vorticella. Propulsive cilia of the polykinety draw water and particles to the peristome, where less active haplokinety cilia filter out the particles. Activity of cilia of both bands transports particles between the two bands towards the cytostome and provides a flow of water out of the infundibulum which can carry away particles that are not ingested. The rates of ciliary action are high and the filtration mechanism is strikingly effective.

All stages in the life cycle of the holotrichous ciliate Ichthyophthirius multifiliis were examined using the scanning electron microscope. Different procedures were used to prepare the tomite, trophozoite and cyst stages. Photomicrographs of freeze dried and critical point dried organisms fixed with glutaraldehyde are presented along with views of trophozoites and tomites deciliated by dibucaine hydrochloride to reveal the pellicle and buccal cavity normally covered by cilia. The holotrichous ciliate Ichthyophthirius multifiliis Fouquet, 1876 is a worldwide obligate ectoparasite of freshwater teleosts (Paperna, 1972; Nigrelli et al., 1976). Epizootics of ichthyophthiriasis rarely occur in freely flowing water (Allison and Kelley, 1963; Kozel, 1976) but can devastate populations of cultured and feral fishes in close confinement, with younger fish being most susceptible (Pillay, 1968). The life cycle has 3 stages termed tomite, trophozoite, and cyst. The small 15 x 40 ,um fusiform tomite, also termed theront, is the infective stage and can survive only 96 hr without a host (Suzuki, 1935). The narrowed anterior end of the tomite possesses a characteristic filamentous projection from a conical depression in the pellicle. This filament differs from the somatic infraciliature in its 3 times greater length and usually rigid orientation (Kozel and Dobra, 1978). Cytochemical techniques have demonstrated a capsule-like structure, also located near the anterior end of the tomite, which contained acid phosphatase and non-specific esterases. The capsule and anterior filament may be part of a perforatorium as cells partially burrowed into host tissues have never been observed to possess a trailing filament (Kozel, 1980). Beckert (1975) considered the tomite to be able to drill its way into the host epithelium with its pointed anterior end and its cilia. After burrowing into the epidermis of the teleost the tomite becomes spherical and develops its oral apparatus. It is now called a trophozoite. The parasite cilia dislodge surrounding host tissue and the trophozoite ingests the debris through its cytostome. The buccal cavity is a rigid cuplike Received 1 June 1984; revised 19 October 1984; accepted 23 October 1984. * Send reprint requests to GWF. t Emeritus Professor of Biology. organ located near the anterior end and is equipped with long cilia that beat continually inward (MacLennan, 1935). The trophozoite grows at a linear rate, dependent on temperature, and leaves the host when it reaches a diameter of 100-1,000 ,um (MacLennan, 1942). The freed trophozoite swims in slow spirals, compared to the tomite, and eventually adheres to surfaces of its environment. A fine gelatinous exocyst is exuded, the oral apparatus is resorbed and schizogony begins. The first 2-4 daughter cells of the schizont form an endocyst of fine anastomosing fibrils that reinforce the exocyst. The endocyst may be formed in more than 1 layer in larger schizonts (MacLennan, 1937). The endocyst(s) and exocyst are not uniform in thickness and for the ultrastructure of these membranes and of the schizonts, the reader is referred to Ewing et al. (1983), and Brown and Gratzek (1980). A large cyst may release up to 1,000 infective tomites to complete the cycle. The purpose of this paper is to present scanning electron micrographs of the entire life cycle of I. multifiliis and the ultrastructure of several surface features. MATERIALS AND METHODS A culture of I. multifiliis was maintained in the laboratory by serial passage on non-immune 8 to 20 cm channel catfish (Ictalurus punctatus) kept in 80-liter aquaria. Water temperature was maintained at 22 C and aeration provided 7-8 ppm dissolved oxygen. The water pH (6-8) was controlled by adding 3 millequivalents/litre of NaHCO3 as a buffer and adjusting with 1 molar NaOH or HC1. Trophozoites were collected by rubbing infected fish by hand in 18-cm diameter syracuse dishes filled with aquaria water filtered through 0.45-micrometer filters and termed biologically conditioned water (BCW). This filtered water served as a culture medium for I. multifiliis allowing the parasite to complete its life cycle. When a number of trophozoites came off the catfish they were transferred by Pasteur pipet through 2 washes of distilled deionized water, 10 min in each wash.

The most rapidly cleared particle size has been reported to increase with the body size of the ciliate, a relationship attributed to changes in the morphological features of the oral apparatus. This study examined the possibility that the spacing of the adoral zone of membranelles (AZM) in Blepharisma japonicum could change or adapt to different sizes of prey. To test this hypothesis, specimens of B. japonicum were cultured on the bacterium Proteus vulgaris, the small ciliate Tetrahymena pyriformis, and smaller individuals of B. japonicum, each of which represented a different size of prey. After completing the culture period, a portion of the AZM was viewed by scanning electron microscopy and measurements of intermembranellar spacing were made from the micrographs. Significant differences (P = 0.01) in intermembranellar spacing were found between treatments: the smaller the prey size, the greater the spacing between the cilia of adjacent membranelles. The relationship between body size and particle size in Blepharisma cannot be explained by the inverse relationship already noted. The possibility remains that other oral structures (e.g., the "gullet") may govern this relationship. In natural waters, the range of food particle sizes often changes seasonally. Therefore, filter feeding organisms would benefit by being adaptable to different particle sizes. Copepods have been shown to shift their grazing pressure from one size of particle to another in order to take advantage of peak particle concentration (Poulet, 1974). Nival & Nival (1976) formulated an equation for filter feeding efficiency from a number of quantitative setal characteristics including setal spacing. They were able to show that the most efficiently filtered particle size increased throughout the maturation of the copepod. Richman et al. (1977) suggested that the flexibility in copepod feeding behavior cannot be explained solely by the mechanism of a fixed sieve, but they admitted not being able to offer an alternative explanation until the kinetics of filter feeding become more clearly understood. Ciliates, like copepods, are suspension (filter) feeders, but unlike copepods, possess cilia rather than setae for filtering. Fenchel (1980a,b) studied suspension feeding organelles and suspension feeding efficiency of ciliates in relation to particle size. He found: (1) that the free space between membranellar cilia determined the minimum size of particle retained; and (2) that the size of particle most rapidly cleared increased with the size class of Blepharisma americanum (see Fenchel, 1980b). He attributed the latter relationship to changes in the morphological properties of the oral apparatus. The oral apparatus of Blepharisma consists of both oral ciliature and cytopharyngeal struc1 We thank David Montagnes, Guy Gilron, and Stephen Wickham for their enthusiastic support and helpful criticism throughout this investigation. Research supported by the Department of Zoology and by N.S.E.R.C. Canada Operating Grant A-6544 awarded to D. Lynn. 2 Person to whom reprint requests should be addressed. TRANS. AM. MICROSC. SOC., 104(4): 333-340. 1985. ? Copyright, 1985, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.27 on Sat, 26 Nov 2016 04:15:15 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC. tures (Giese, 1973). The two major components of the oral ciliature are: (1) the adoral zone of membranelles (AZM), which functions to set up a vortex and draw in food particles from the surrounding water; and (2) the undulating membrane, which directs the particles into the cytostome (Giese, 1973; Sleigh & Barlow, 1982). Since the AZM functions to concentrate the food particles, it also may function in the selection of particle size (Fenchel, 1980a). In the present study, intermembranellar spacing was chosen as a possible site of long-term adaptation. The membranelles of the AZM are anchored by microtubular rootlets interconnected with microfilaments (Dembitzer & Hirshfield, 1966; Giese, 1973). By contraction of the filamentous components, the ciliate may be able to change intermembranellar spacing. However, Fenchel's (1980b) study assumed that intermembranellar spacing is more or less constant for a species. We assumed, then, for the purposes of this study, that the intermembranellar spacing is constant and does not change or adapt to prey size. Blepharisma were fed natural prey organisms to test for the possibility of adaptation of intermembranellar spacing to size of prey after several weeks of exposure to prey. Exposure to actual prey represents a more plausible ecological situation than using latex beads (Fenchel, 1980b) since the prey organisms chosen are known to support growth of Blepharisma (see Giese, 1973). Since a ciliate is more likely to encounter a monospecific patch of prey organisms in the natural environment, Blepharisma has been grown with one prey species at a time. MATERIALS AND METHODS

In an effort to establish comparative data within the genus Leucocytozoon, elongate gametocytes of L. ziemanni from naturally infected great horned owls (Bubo virginianus) were exam- ined by electron microscopy. Micro- and macrogametocytes proved to be easily distinguishable at the electron microscopic level due to dramatic dimorphism at maturity and cytoplasmic and nuclear morphology. The parasite membrane architecture, number and type of cytoplasmic ribosomes of both micro- and macrogametocytes, presence and arrangement of osmiophilic bodies and electron dense spheres, mitochondrial morphology, endoplasmic reticulum cisternae morphology, mitochondria con- taining pocket infoldings of the nuclear membrane of the microgametocytes, and cytostome and food vacuole formation compare favorably with available information on L. simondi and L. smithi. Com- parative variations exist only in that L. ziemanni gametocytes apparently lack compartmentalization of the cytoplasm by aligned unit membranes and parasite induced separations of the host cell nu- cleus as reported for L. simondi. The ultrastructure of gametocytes of vari

The erythrocytic stages of a reptilian malarial parasite, Plasmodium floridense, were studied for the first time with the electron microscope. The fine structure of the erythrocytic stages of this reptilian parasite was compared with the erythrocytic and exoerythrocytic stages of avian parasites and the erythrocytic stages of mammalian parasites. The overall structure and developmental sequence of P. floridense are essentially similar to those of avian and mammalian malarial parasites. The merozoite possesses all of the organelles which have been described in the merozoites of avian and mammalian parasites. However, we also noticed large less-electron-opaque rounded bodies of unknown nature located near the paired organelles in the merozoite of P. floridense. The dedifferentiation phase is also observed in P. floridense in that certain organelles of the merozoite are lost, such as an anterior end structure (conoid), paired organelles, dense bodies, spherical body and the thick inner membrane and a layer of microtubules of the pellicular complex. During the growth phase, the cytostome of P. floridense ingests host cell cytoplasm and forms food vacuoles. Nuclear division is also similar to that of avian and mammalian malarial parasites. The redifferentiation phase is initiated by the reappearance of the thick inner membrane, paired organelles and anterior end structure (conoid), as we have observed in other species of malarial parasites. The budding of the merozoites from a schizont occurs at the areas which are covered by the thick inner membrane. By the migration of various organelles into the budding areas, several merozoites are formed from a schizont as we have observed among avian and mammalian malarial parasites. A reptilian malarial parasite, Plasmodium floridense, was first described in Sceloporus undulatus and Anolis carolinensis by Thompson and Huff (1944) and the infection of P. floridense has been extensively studied by Goodwin (1951) and Jordan (1964). Though there are considerable studies on the fine structure of the erythrocytic and exoerythrocytic stages of avian (Rudzinska and Trager, 1961; Ristic and Kreier, 1964; Aikawa, 1966; Aikawa et al., 1967; Meyer and Oliveira Musacchio, 1965; Hepler et al., 1966) and mammalian (Rudzinska and Trager, 1959, 1968; Rudzinska et al., 1965; Ladda et al., 1966, Aikawa et al., 1966b) malarial parasites, no report has been made on reptilian malarial parasites. We have, therefore, undertaken a study of the reptilian malarial parasite, P. floridense, and investigated the possibility of morphological and developmental differences in ultrastructure between the reptilian parasite and avian and mammalian parasites. MATERIALS AND METHODS Sceloporus undulatus infected with P. floridense was obtained in Clinch County, Georgia, in the vicinity of the Okefenokee Swamp. Blood from these lizards with 1 to 5% parasitemia was fixed Received for publication 7 June 1968. * Contribution No. 399 from the Army Research Program on Malaria. in 1.25% glutaraldehyde solution with 0.05 M phosphate buffer at pH 7.3 and containing 4% sucrose for 1 hr at room temperature. The blood was centrifuged for 10 min at 200 g. The resulting pellets were washed several times in 0.05 M phosphate buffer solution for at least 1 hr. Following the wash, the pellets were postfixed in 1% Os04 for 1 hr. The pellets were dehydrated in an ascending ethanol series and in propylene oxide and embedded in Epon 812. Thin sections were cut on a Porter-Blum MT-2 ultramicrotome with a Dupont diamond knife. The sections thus obtained were mounted on 300-mesh copper grids and stained with 1% uranyl acetate and lead citrate. The material was examined with a Siemens Elmiskop 1A. OBSERVATIONS AND DISCUSSION The merozoites of the erythrocytic stages of Plasmodium floridense are similar to those of certain avian (Aikawa, 1966; Aikawa et al., 1967; Hepler et al., 1966) and mammalian (Aikawa et al., 1966b; Aikawa, 1968) parasites. These include P. fallax, P. lophurae, P. cathemerium, P. gallinaceum, P. elongatum, P. berghei, P. knowlesi, and P. cynomolgi. The organelles of the merozoites include an ante ior end structure (conoid*) with polar rings, pa red organelles, dense bodies, a mitochondrion, a spherical body, a nucleus, ribosomes, endoplasmic reticulum, a cytostome, a pellic* Our use of the term "conoid" differs from the original use of Gustafson et al. We use the term to refer to the truncated anterior end.

The genus Embadomonas was founded by Mackinnon (1911) to include two species of flagellates (E. agilis and E. alexeieff) obtained from tricopterous larvae. According to Mackinnon (1915), to this genus belong "small slipper-shaped flagellates, characterized by a very large cytostome bordered by prominent lips, which are more or less siderophilous, and two flagella not so long as the body, one acting as an organ of locomotion, and the other lying in the cytostome; the spherical nucleus is placed at the anterior end of the body; the two basal granules from which rise the flagella, lie at the anterior border of the cytostome. There is a definite periplast, which prevents deformation of the body. The anterior part of the body shows a well marked torsion. The cysts are relatively small, and are ovoid in form." Since then other species have been discovered. Wenyon and O'Connor (1917) described E. intestinalis from man; da Fonseca (1920), E. wenyoni ("Waskia") from the monkey Cebus caraya. Faust and Wassell (1921) described E. sinensis from man but from the figures of Faust (1922) there is some likelihood that they were dealing with a flagellate of another genus, since the posteriorly directed flagellum is not shown emerging from the cytostome or lying within it for any of its length as is the case in other species belonging to this genus. In some respects the new species, described since the founding of the genus by Mackinnon, do not conform with the original generic description, but there is general agreement with respect to the presence of two flagella, one of which is directed anteriorly and the other, posteriorly, the latter lying either wholly within the cytostome or for only the proximal portion of its length. In some forms this flagellum is shorter and thicker than the anterior flagellum. We do not accept the statement of da Fonseca (1920) that flagellates of the genus Embadomonas possess an undulating membrane in the cytostome for none of the observers who have studied various species of this genus has recorded such a finding and moreover his description of the genus "Waskia" is definitely synonymous with Embadomonas as given by Mackinnon except for the description of "double" forms which, however, are doubtless division forms.