Observations on the ultrastructure of Haemogregarina simondi in the marine flatfish Solea solea (L.).

Developing stages of Haemogregarina simondi from the marine fish Solea solea (L.) were examined by electron microscopy. Merozoites lay in a parasitophorous vacuole and were bound by a pellicle of three unit membranes beneath which lay a ring of 45--61 microtubules. The cytoplasm contained 4--6 rhoptries, more than 169 micronemes, several mitochondria, and amylopectin granules. A conoid and one polar ring were observed at the anterior end. Intraleucocytic and intraerythrocytic schizonts with up to eight merozoites were described also. Intraerythrocytic and free gametocytes were characterized by distinct refractile bodies and a pellicle consisting of only two unit membranes. The number of micronemes was in excess of 194. The results were discussed in comparison with other members of the Haemogregarinidae.     

Structure, Cytochemistry, and Locomotion of Haemogregarina sp. from Rana berlandieri

Intra- and extracellular gametocytes of Haemogregarina sp. from Rana berlandieri were studied by light and electron microscopy. Locomotion in free gametocytes appears to be related to series of horizontal “peristaltic” waves of constriction, passing from anterior to posterior along the body. Intracellular gametocytes lie within a vacuole in the erythrocyte cytoplasm. The pellicle of the parasite consists of a trilaminar plasmalemma and an inner electron dense layer, beneath which lies a ring of 80 microtubules. The inner dense layer becomes thickened and modified in the apical region, to form a cap-like structure. The gametocytes contain a prominent nucleus, several mitochondria, and many granular inclusions. One type of inclusion consists of elliptical, electron-dense, profeinaceous bodies scattered throughout the cytoplasm, while other inclusions are larger and electron-opaque, polysaccharide in nature, and occur predominantly in the pre- and post-nuclear regions. In the electron microscope, pronounced pellicular folds were observed in longitudinally sectioned extracellular gametocytes. These folds are thought to represent the waves of constriction seen in motile specimens by light microscopy. The mechanism of movement of the parasite is discussed and compared with that in haemosporidian ookinetes, as well as in gregarines.     

The Fine Structure of Rhynchocystis pilosa (Sporozoa, Eugregarinida)

SYNOPSIS. The trophozoite of Rhynchocystis pilosa obtained from the seminal vesicles of the earthworm Lumbricus terrestris was studied by light and electron microscopy. The trophozoite's cortical organization is particularly interesting because of its unusual evaginations and associated fibrillar structures. The pellicle is formed by 2 concentric membranes elevated into 60–70 alternating primary and secondary ridges extending posteriad. Numerous long ‘hairs’ or cytopilia originate along the primary ridges and each contains a system of fibrils originating from an underlying longitudinal myoneme. Longitudinal rows of pores lie between adjacent pollicular ridges. Three systems of fibrils lie in the cortex of the trophozoite. A longitudinal myoneme consisting of 12–18 fibrils lies below each primary pellicular ridge. Circular myonemes lie below the pellicle in a parallel array along the length of the organism. Each myoneme consists of 4–8 fibrils structurally similar to those of the longitudinal myonemes. Pairs of fine filaments also lie in the inner pellicular membrane along the apex of each ridge. The trophozoite's anterior end is modified as an attachment organelle consisting of 30–35 delicate pellicular folds which originate at the base of an anterior papilla. The folds extend approximately 15 μ posteriad where they become continuous with the primary pellicular ridges. The nucleus lies in the cytoplasm near the posterior level of the attachment organelle and is surrounded by a double membrane perforated by numerous pores. The cytoplasm contains numerous small vesicles which may be found in dense aggregations. These aggregations often occur in proximity to Golgi complexes and certain membrane-bound bodies. Mitochondria are abundant in the cytoplasm as are large, ovoid paraglycogen bodies. Occasionally layers of granular membranes are arranged parallel to the surface of the paraglycogen bodies but also occur thruout the cytoplasm.     

THE ULTRASTRUCTURE OF THE PELLICLE COMPLEX OF EUGLENA GRACILIS

The pellicle complex of E. gracilis is composed of the cell membrane, the ridge and groove with the notch, four fibrils, and the subpellicular ER. The cell membrane is of unit membrane configuration and covers the outside of the cell, the cytostome, the gullet, and the reservoir. The notch of the pellicle complex has always a close topographic relationship to two particular fibrils, as well as the subpellicular ER. The gullet is that region between the reservoir and the cytostome which, in addition to longitudinal fibrils, is surrounded by a single row of circular fibrils. The circumference of the cytostome has twenty large pellicular ridges alternating with small pellicular ridges. Alternating tall and small pellicular ridges cover the entire cell during division.     

Fine Structure of Gametogony and Oocyst Formation in Sarcocystis sp. in Cell Culture

Fine structure of gametocytes and oocyst formation of Sarcocystis sp. from Quiscalus quiscula Linnaeus grown in cultured embryonic bovine kidney cells was studied. Microgametocytes measured up to ～5 μm diameter. During nuclear division of the microgametocyte, dense plaques were found adjacent to the nucleus just beneath the pellicle; occasionally microtubules were present within these plaques. These microtubules subsequently formed 2 basal bodies with a bundle of 4 microtubules between them. Microgametocytes also contained numerous mitochondria, micropores, granules, vacuoles, and free ribosomes. Each microgamete was covered by a single membrane and consisted of 2 basal bodies, 2 flagella, a bundle of 4 microtubules, a perforatorium, a mitochondrion, and a long dense nucleus which extended anteriorly and posteriorly beyond the mitochondrion. The bundle of 4 microtubules is thought to be the rudiment of a 3rd flagellum. Macrogametes were covered by a double membrane pellicle, and contained a large nucleus (～2.5 μm), vacuoles, and a dilated nuclear envelope connected with the rough endoplasmic reticulum (ER). In young macrogametes (～4 μm), the ER was arranged in concentric rows in the cortical region, and several sizes of dense granules were found in the cytoplasm. However, in later stages (～8 μm) the ER was irregularly arranged and was dilated with numerous cisternae; only large dark granules remained and a few scattered polysaccharide granules were found. No Golgi apparatus or micropores were observed. After the disappearance of dark granules 5 concentric membranes appeared. Four of these fused to form an oocyst wall composed of a dense outer layer (～66 nm thick) and a thin inner layer (～7 nm). The 5th or innermost membrane surrounded the cytoplasmic mass which was covered by a 2-layered pellicle and contained a nucleus, small amounts of ER, large vacuoles, and mitochondria. The sexual stages described greatly resemble those of Eimeria and Toxoplasma.     

Aspects of the sporogonic development of Leucocytozoon tawaki of the Fiordland crested penguin in its primary vector, Austrosimulium ungulatum: an ultrastructural study.

Early oocysts of Leucocytozoon tawaki Fallis, Bisset and Allison were located between the basal lamina and the midgut epithelium of the vector, Austrosimulium ungulatum. The spherical oocysts were surrounded by an amorphous, electron-dense wall and contained a large, central core of closely spaced dense particles, the crystalloid inclusion. Around the latter were many concentrically arranged cisternae of granular endoplasmic reticulum. A few large, poorly defined nuclei, some of which contained spindle apparatus, were seen. Sporozoite formation occurred around the peripheral cytoplasm of maturing oocysts. The sporozoite pellicle was subtended by 30 microtubules which appeared to originate from the most posterior of 3 dense, polar rings. Each forming sporozoite contained a central nucleus, mitochondrion, and a crystalloid inclusion both anterior and posterior to the nucleus. The nature and significance of the crystalloid in Leucocytozoan species and other apicomplexans is discussed with special reference to similar viruslike inclusions in the sporogonic stages of certain species of Plasmodium.     

The Fine Structure of Two Archigregarines, Selenidium fallax and Ditrypanocystis cirratuli

SYNOPSIS. In S. fallax and D. cirratuli the pellicle is thrown into longitudinal folds. The pellicle consists of 2 membranes, one 3-layered, the other 5-layered. Sub-pellicular fibrils, each about 23 mμ in diameter run along the pellicular folds. Pellicle and sub-pellicular fibrils together form the mechanism by which Selenidiids move. The undulating membranes of D. cirratuli are enlarged pellicular folds, the tips of which are packed with fibrils. The light ovoid patches seen in thin sections are sections through regions which contain a form of glycogen in the living animals. Typical mitochondria are absent. Objects described as lipochondria have a regular distribution at the bases of the grooves in the pellicle and are probably formed from the inner components of the pellicle.     

Gametogenesis, fertilization and ookinete differentiation of Leucocytozoon smithi

Development of Leucocytozoon smithi during gametogenesis, fertilization, and ookinete differentiation was studied by light and electron microscopy. Gametogenesis occurred rapidly, within 1-2 min after gametocytes were ingested by black flies. Usually one axoneme, but not infrequently two, was observed in microgametes. The macrogamete nucleus was characteristically elongated and fragmented, with a convoluted nuclear envelope. Fertilization occurred within five min after ingestion of gametocytes by the vector. The entire axoneme and nucleus of the microgamete entered the cytoplasm of the macrogamete. Zygote differentiation resembled sporozoite formation in that a thickened inner membrane and subpellicular microtubules developed beneath the plasmalemma, followed by cytoplasmic protrusion or evagination to form the anterior end. Extension of the inner thickened membrane continued as the zygote elongated. Development of sausage-shaped ookinetes was completed within 6-8 h after ingestion of a blood meal by a black fly. Mature ookinetes possessed a single nucleus, double-layered pellicle, canopy, apical pore, polar ring complex, subpellicular microtubules, micronemes, crystalloids, abundant mitochondria, endoplasmic reticulum, and ribosomes. Comparison of development of L. smithi with species of Plasmodium and Haemoproteus revealed general similarities in both sexual and asexual development within the insect vector. A diagram summarizing life cycle events for L. smithi is included.     

The Ultrastructure of Lankesterella hylae

SYNOPSIS. The ultrastructure of Lankesterella hylae was studied and numerous points of similarity to Plasmodium, Toxoplasma, Sarcocystis and Lankesterella garnhami were found. The protozoa were intracellular and lay within vacuoles containing vesicles, unusual membrane formations and dense granular material. The parasite was invested by a double membrane and had a micropyle, as well as membranous processes extending from the surface. At the anterior end were conoid and apical rings. The cell contained a nucleus, nucleolus, bipolar paranuclear vacuoles or bodies, a series of microtubules beneath the pellicle, endoplasmic reticulum, mitochondria, toxonemes and a variety of vacuoles. In addition, dense particles, similar to those related to the endoplasmic reticulum, were scattered throughout the cytoplasm.
The unusual membrane formations and vesicles in the periparasitic vacuoles were striking observations possibly related to the nutrition of the parasite.     

Fine Structure of Schizonts and Merozoites of Eimeria nieschulzi*

SYNOPSIS. Schizonts of E. nieschulzi lie in a vacuole within the host cell. After nuclear division the cell membrane invaginates forming merozoites. Differentiation of the pellicle and other organelles occurs while merozoites are still attached to the schizont cytoplasm. Merozoites have a pellicle thickened at the anterior end to form a polar ring. Radiating posteriorly from the ring, directly beneath the pellicle, are about 25 microtubules. Within the polar ring is a dense conoid. Extending posteriorly from within the conoid is a paired organelle. The paired organelle varies in size and shape in each generation of merozoites. Numerous toxonemes occupy the anterior half of the merozoites. Two paranuclear bodies are present in 1st generation merozoites. One or 2 granular bodies were seen in the anterior end of 2nd generation merozoites. In 3rd generation merozoites 6 or more granular bodies were seen anterior to the nucleus. Each merozoite has a single nucleus containing diffuse chromatin material. Elongate mitochondria and glycogen granules are present. The vacuole surrounding mature merozoites contains residual cytoplasm of the schizont and some granular material. Microvilli project into the vacuole from the host cell membrane.     

Ultrastructure of Spermatozoa in the Nematode Halalaimus dimorphus (Nemata: Oxystominidae)

The ultrastructure of spermatozoa in the free-living marine nematode Halalaimus dimorphus was studied with transmission electron microscopy. Spermatozoa in the posterior testis of the male had a large cavity filled with cellular processes, which contained a variable number of small tubules. Mitochondria and small tubules were the only cell structures observed in the cytoplasm. The spermatozoa had a bipolar structure. The anteriorly situated nucleus, which was electron-dense and homogeneous, was surrounded by a single membrane. The size of the small tubules in the cytoplasm (diam. 12-13 nm) and their relatively thick wall structure suggested that they were not normal microtubules (diam. 25 nm). The material of the small tubules was assumed to be major sperm protein (MSP). The cavity appeared to open on the surface of the spermatozoon at the posterior extremity of the cell, and also medially, at the level of the anterior end of the cavity. The pores apparently were closed by a special plug-like structure, which was an evagination of the cell. The wall of the cavity was characterized by longitudinal folds, which were mushroom-shaped in transverse section. Spermatids in the anterior testis of H. dimorphuswere characterized by fibrous bodies packed with small tubules and by cellular processes also containing small tubules. H. dimorphus sperm seem to perform swimming movements based on liquid currents commonly present in turbin-like systems. Spermatogenesis resembled that found in ticks.     

Observations on the Fine Structure of the "Cyst Stage" of Besnoitia jellisoni

SYNOPSIS. Light and electron microscope studies of the "cyst" of Besnoitia jellisoni indicate that it consists of an extracellular wall, a large, sometimes multinucleate, host cell, and an intracellular vacuole containing the parasites. The "cyst" wall has fine fibrils and small dense granules embedded in an election-lucid matrix. The wall may be formed from a secretion of the enclosed host cell. The plasma membrane of the host cell is very irregular, being modified into microvillar or pseudopodial extensions. Small vesicles and invaginations of the plasma membrane indicate mioropinocytosis. The one to several large lobular nuclei lie in a thick area of cytoplasm which is filled with rough endoplasmic reticulum and many mitochondria with lamellar cristae. The parasite-containing vacuole is limited by a vacuolar membrane which has many blebs suggesting a transfer of materials into the vacuole.
The "cyst" organisms are crescentic or piriform and are enclosed by a pellicle consisting of outer and inner membranes. Twenty-two subpellicular fibrils extend longitudinally adjacent to the inner membrane from the anterior polar ring to a posterior ring. A micropyle is situated laterally in the pelliole near the level of the nucleus. A conold and several associated paired organelles are present at the anterior end. Microuemes, more abundant in older organisms, are also present in the anterior portion of the parasite. A Golgi apparatus lies adjacent and anterior to the nucleus. One or more mitochondria with saccular cristae, ovoid glycogen bodies, free ribosomes and occasional vacuoles are also present. Organisms within the "cyst" multiply by endodyogeny.     

The Fine Structure of Haemoproteus columbae Sporozoites*

SYNOPSIS. The fine structure of Haemoproteus columbae sporozoites has been studied and compared to sporozoite structure as revealed by the light microscope. The sporozoites are ultrastructurally similar to those of other Haemosporidia in that they possess a 3-layered pellicle, subpellicular microtubules, polar ring, micropore, free ribosome-like particles, micronemes, a structure resembling a Golgi complex, an irregular mitochondrion, and a large nucleus. In the anterior region of the sporozoite there are 21–22 regularly arranged longitudinal subpellicular microtubules located peripherally around the cell. In the apical region the microtubules appear thickened on 1 side. The sporozoite of H. columbae has a microneme system in which 1–3 micronemes are associated with the outer pellicular membrane at the anterior end. Micronemes are found throughout the cytoplasm, but occur in greater concentration in the anterior region of the sporozoite. A clear pellicular cavity, located between the polar ring and the termination of the inner pellicular layer, is present at the anterior end of the sporozoite. Vesicular invaginations of the inner pellicular layer have been observed in the anterior region; their function is unknown. Spherical osmophilic bodies are found throughout the cytoplasm.     

Electron Microscope Studies on Eimeria perforans (Sporozoa)

SYNOPSIS. By means of electron microscopy, a study has been made of the fine structure of the macrogametocytes, microgametocytes and oocysts of Eimeria perforans from the intestine of the wild rabbit (Oryctolagus cuniculus). The parasites lie in a vacuole within the host cell. The surface of the gametocytes is not plain, but displays irregular protrusions. A large intranuclear body can be detected within the macrogametocytes. Similar structures are also found within the cytoplasm. Within the latter there exists a large spread out reticulum, the channels and vesicles of which concentrate especially close to the nuclear membrane. Tubuli are seen in the numerous mitochondria, which often have a dumb-bell shape.
In most of the gametocytes irregular, strongly osmiophilic lipid inclusions are observed, which always are surrounded by the endoplasmic reticulum. Strange folded ovoid bodies are found within the cytoplasm of the oocysts. Nothing can be told with certainty of their nature and function. Probably they represent specific storage bodies.     

CYTOCHEMICAL LOCALIZATION OF ACID PHOSPHATASES IN EUGLENA GRACILIS

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.     

New Observations on Gametogenesis,Fertilization, and Zygote Transformation in Plasmodium gallinaceum1

The ultrastructure of the sexual stages of Plasmodium gallinaceum during gametogenesis, fertilization, and early zygote transformation is described. New observations are made regarding the parasitophorous vacuole (PV) of gametocytes and the process of emergence in male and female gametocytes. Whereas female gametocytes readily disrupted both the PV membrane and host cell plasmalemma during emergence, male gametocytes frequently failed to break down the plasmalemma of the host cell. New observations and hypotheses are presented on the behavior of the male gamete nucleus. Following fertilization, the male nucleus appears to travel through a channel of endoplasmic reticulum in the female gamete before fusing with the female nucleus at a region in which the nuclear envelope is thrown into extensive convoluted folds. Polarization of the zygote nucleus, in association with the appearance of a perinuclear spindle of cytoplasmic microtubules, preceded all other changes in the developing zygote. After nuclear polarization becomes apparent, electron-dense material is deposited beneath the zygote pellicle, and a canopy is formed which eventually extends over the entire apical end of the developing ookinete. As the apical end begins to extend outward, polar rings, micronemes, and subpellicular microtubules become visible in this portion and a “virus-like” inclusion known as a crystalloid is formed in the posterior portion of the zygote. When female gametes are prevented from being fertilized, the cytoplasm at 24 h after gametogenesis is devoid of most of those organelles found in the developing zygote or the mature ookinete. The cell is surrounded only by a single membrane. Although at various points beneath the membrane there are deposits of electron-dense material reminiscent of those deposited in the zygote, no further development of ookinete structures takes place in the unfertilized female gamete.     

Cytology of a chromophobe pituitary adenoma. A case report

A pituitary tumor with suprasellar and extrasellar extension was investigated by means of the squash-smear cytologic technique. The dominant cell type was large, round to oval cells, with pale-staining, finely granular cytoplasm. The nuclei of these cells often contained single or multiple inclusions of uncertain nature. There also were cells with eosinophilic cytoplasm, usually collected in small nests. Hyperchromatic "naked" nuclei, in various shapes, were immersed in a homogeneous, faintly staining ground substance. Mitotic figures were detected easily. Cytology of these combined cell types allowed the intraoperative diagnosis of a rather pleomorphic pituitary adenoma.     

An Ultrastructural Study of Eimeria iroquoina Molnar & Fernando, 1974 in Experimentally Infected Fathead Minnows (Pimephales promelas,Cyprinidae) 3. Merogony1

Fathead minnows, Pimephales promelas, raised from eggs in the laboratory, were experimentally infected with oocysts of Eimeria iroquoina from either P. promelas or the common shiner, Notropis cornutus. Within intestinal epithelial cells, trophozoites thought to be derived from the sporozoites contained a prominent electron-dense refractile body. Merozoites dedifferentiated into trophic forms by losing components of their apical complex and pellicle. The inner membrane components of the pellicle appeared discontinuous, and the micronemes became enclosed within vacuoles. Prior to merozoite formation, multinucleate meronts were limited by a single membrane. Golgi complexes were associated with the nuclei of this stage. Merozoites were formed by ectomerogony in one generation and by endomerogony in the final generation. In both forms of merogony the final nuclear division was coupled with the onset of differentiation of the merozoites and featured eccentric mitotic spindles associated with centrocones located within the nuclear envelope and with the precursors of the apical complex. A Golgi complex was closely associated with the nucleus and apical tip of the forming merozoite. Unlike other Eimeria species, the complete pellicle of the merozoites of the final asexual generation of E. iroquoina was formed within the cytoplasm of the meront, without association with the limiting membrane, thus, all pellicular components are synthesized de novo. The inner membranes of the pellicle initially appeared as longitudinal strips, each of which was associated with a pair of the 22–24 subpellicular microtubules. Mature meronts of the final asexual generation averaged 9 μm in diameter and produced 13–16 merozoites. With the exception of the internal completion of the pellicle of the final generation merozoites, the basic processes of merogony in fish Eimeria species are similar to those recorded in terrestrial hosts.     

Fine Structure of Haemoproteus columbae Kruse During Differentiation of the Ookinete*

Ookinete differentiation begins in vitro～1 hr after blood infected with mature gametocytes of Haemoproteus columbae is withdrawn from a pigeon. In the undifferentiated zygote, dense material accumulates at the point under the plasma membrane. The conoid and conoidal rings condense from this material. The nucleus is drawn out to a point with the intranuclear spindle (INS) at the peak. Atypical centrioles lie under the forming conoid in the cytoplasm next to the INS. Fibrous material under the inner membrane forms the polar ring from which subpellicular microtubules originate. One hr later the centrioles have disappeared and the nucleus has returned to the center of the organism. The conoidal complex forms the tip of a growing cytoplasmic projection, the anterior end of the ookinete. During this time an elaborate pellicle is differentiating antero-posteriorly; crystalloid formation begins with an extensive proliferation of rough endoplasmic reticulum (ER) continuous with the outer membrane of the nuclear envelope. Crystalloid particles are formed between the lamellae of the ER and collected in a sphere that is later partially surrounded by a small amount of ER. Ookinetes, differentiated 2 hr longer than the ookinetes in vitro, were obtained from the gut of the pigeon fly, Pseudolynchia maura. The differentiated pellicle of these ookinetes consists of a plasma membrane, an inner membrane layer composed of 2 appressed membranes, and in the anterior end, an electron-opaque lamina immediately under the inner membrane. Anterior to the polar ring, this lamina forms a canopy which, posteriorly, is drawn out into projecting ribs which diminish and disappear in the first third of the organism. Fifty to 60 subpellicular microtubules insert on the polar ring. Ookinetes differentiated in vitro were no more than 4 hr old. They lacked micronemes and retained a pellicular cytostome and “internal cytostomes.” The differentiation of micronemes probably occurs at a later time because they are visible after 6 hr in ookinetes in the fly gut. So many degenerating organisms appeared in vitro after 5 hr that this material was discarded.     

ASPECTS OF CILIARY FINE STRUCTURE IN EUPLOTES PATELLA

1. The functional unity of cirri and membranelles can result structurally only from extensions of the ciliary membrane. 2. The pellicle is composed of an outer pellicular membrane and an inner cytoplasmic membrane. 3. The ciliary rootlets are composed of numerous filaments 120 A in diameter with central areas of low density. They have no periodic structure. 4. The ciliary membrane is a double-layered structure continuous with the pellicular membrane. The cilia show the typical arrangement of nine double, peripheral and two single, central fibrils. All fibrils pass into the basal region, the peripheral ones joining with the rootlet filaments, while the central fibrils from the extreme proximal position of the basal region turn back toward the pellicle and appear to unite just beneath the cytoplasmic membrane. 5. The cilia (300 mµ diameter) taper at their tips to a diameter at least as small as 50 mµ. At a diameter of about 150 mµ, the fibrils begin to show a reduction in number. 6. The central ciliary fibrils may determine the possible directions of ciliary beat. These fibrils show an intrafibrillar structure in their basal portion, which involves regularly spaced 40 A granules. 7. These observations on Euplotes, together with the other evidence cited, are consistent with the hypothesis that ciliary motion is produced by the contraction of the peripheral fibrils, while the central fibrils perhaps determine the plane in which the cilia can bend.