The fine structure of photoreceptors in a marine flatworm

Summary The ocelli or eyes of the marine polyclad turbellarian Notoplana acticola are clustered on the paired dorsal nuchal tentacles and in two longitudinal bands lateral to the cerebral ganglion. The ocelli, studied by electron microscopy, were characterized as rhabdomeric and non-ciliary in origin. There are 60 to 80 ocelli per animal each enclosed in a fibrous capsule to which muscle fibers may attach. An ocellus consists of a pigmented eyecup into which 30 to 50 photoreceptor cells send dendritic processes through interruptions in or among pigment cell projections across the eyecup opening. The dendritic processes terminate in numerous long intertwined microvilli which fill the eyecup. The nucleated cell body of each photoreceptor cell lies outside the eyecup and projects an axonal process to the cerebral mass. Within the dendritic processes are observed mitochondria, ribosomes, neurotubules, multivesicular bodies, vesicles and vacuoles. The cell body contains smaller mitochondria, endoplasmic reticulum, ribosomes, vesicles and prominent Golgi complexes.After dark adaptation, there are some structural alterations in terms of swelling of microvilli, increased numbers of vacuoles associated with the microvilli and dendritic processes, and changes in the pigment cell projections.This work was supported by Grant No. GM 10292 from the U.S. Public Health Service to Professor Richard M. Eakin, Department of Zoology at the University of California, Berkeley, U.S.A., where this investigation was conducted during the author's sabbatical leave of absence from the University of Illinois, and by Grant No. 1 SO 1 FR 5369 from the U.S. Public Health Service to the University of Illinois at the Medical Center.I express appreciation to Professor Eakin for interesting discussions and generous hospitality to me as a guest in his laboratory, and to the John Simon Guggenheim Memorial Foundation for the Fellowship which I held during 1964–65. I thank Dr. John P. Marbarger, Director of the Aeromedical Laboratory for the electron microscope facilities used at the University of Illinois.     

An ultrastructural study of the carotid body of horse and dog

Summary Carotid body tissue from horse and dog has been investigated ultrastructurally. Several cell types are recognized: glomus cells which are regarded as chemoreceptors, sustentacular cells which enclose the glomus cells, and nerve fibers.The glomus cells contain electron dense granules which are interpreted as packages of biogenic monoamines. There are both dark and light glomus cells, the former containing more granules and ribosomes. Invaginations of the plasma membranes as well as free coated vesicles are often seen in the cytoplasm of glomus cells. Nerves within the glomus lobules are generally wrapped by sustentacular cells, but nerve endings are also seen in close contact with the glomus cells. Some endings contain synaptic vesicles as well as a great concentration of mitochondria. The corresponding fibers are thought to be efferent. Another type of contact is interpreted as en passant synapses of afferent fibers.The author wishes to express his gratitude to Professor L. Nicander who initiated this project and took most of the micrographs and to Professor Nils Obel and associate Professor Gustav Björk at the Royal Veterinary College for their valuable help with the surgical procedure and to Dr. Martin Ritzén of the Royal Medical College for making the tests for biogenic monoamines.     

The fine structure of sensory receptor processes in the auricular epithelium of the planarian,Dugesia tigrina

Summary The marginal epithelium of the lateral auricles of the planarian, Dugesia tigrina, includes a cell type with surface cilia and microvilli, a basal nucleus, and dense cytoplasm containing secretory vacuoles, Golgi elements, mitochondria and ribosomes. Through channels within the epithelial cytoplasm, cellular processes, interpreted as extensions of neurosensory receptor cells located in the subepidermis, project to the surface. The receptor processes, containing microtubules, mitochondria, vesicles and an agranular tubular reticulum, project beyond the epithelial cell surface; one or two cilia each emerge from a basal body in the apex of the projection. Close to the point of emergence to the epithelial surface, each cylindrical receptor process is surrounded by a collar-like septate junction between adjacent plasma membranes. The cilia of the projections differ from those of the epithelial cells in diameter, density of matrix and in the banding patterns of the rootlets. A few projections appear with the apex and basal body retracted below the epithelial surface. The possible function of these ciliated processes in sensory reception is discussed.This work was supported by Grant No. SO 1 FR 5369 from the U.S. Public Health Service to the University of Illinois at the Medical Center.I thank Dr. J. P. Marbarger, Director of the Research Resources Laboratory, for use of the electron microscope facilities, Miss Irena Kairys for technical help, Miss Marie Jaeger for assistance with photography, and Mr. Robert Parshall for the drawing.To Professor Arthur Wagg Pollister, I respectfully dedicate this article on the occasion of his retirement from Columbia University.     

The fine structure of ependymal cells part II: An electron microscopic study of the soft-shelled turtle paraventricular organ,with special reference to the fine structure of ependymal cells and so-called albuminous substance

Summary The present study deals with the electron microscopic observations on the softshelled turtle paraventricular organ, with special reference to the relationship of the ependymal cells and the so-called albuminous substances. It is shown that the so-called albuminous substances consist of the tips of neuronal processes extending into the ventricular lumen. They probably arise from the nerve cells lying within the hypendymal or the underlying tissue. The ependymal cells of the PVO themselves are basically similar in structure to those of any other animal.The processes observed contain two types of vesicles, namely: the clear vesicle, 500 to 1600 Å in diameter, and the cored vesicle, measuring 600 to 1500 Å in diameter, which has a distinct membrane enclosing an extremely dense core of variable sizes. The functional significance of these vesicles is discussed in relation to that of inclusions in the neurosecretory and the autonomic nerve fibers in the hypothalamus.The findings indicate that in the terminal endings of the processes a production or formation of vesicles might occur and that these vesicles might be discharged into the cerebrospinal fluid by microapocrine secretion.The author's grateful thanks are due to Prof. E. Yamada for his continuously kind guidances and due to Prof. T. Sakurai for his constant encouragement.     

Synaptic relationships in the plexiform layers of carp retina

Summary The synaptic contacts made by carp retinal neurons were studied with electron microscopic techniques. Three kinds of contacts are described: (1) a conventional synapse in which an accumulation of agranular vesicles is found on the presynaptic side along with membrane densification of both pre- and postsynaptic elements; (2) a ribbon synapse in which a presynaptic ribbon surrounded by a halo of agranular vesicles faces two postsynaptic elements; and (3) close apposition of plasma membranes without any vesicle accumulation or membrane densification.In the external plexiform layer, conventional synapses between horizontal cells are described. Horizontal cells possess dense-core vesicles about 1,000 Å in diameter. Membranes of adjacent horizontal cells of the same type (external, intermediate or internal) are found closely apposed over broad regions.In the inner plexiform layer ribbon synapses occur only in bipolar cell terminals. The postsynaptic elements opposite the ribbon may be two amacrine processes or one amacrine process and one ganglion cell dendrite. Amacrine processes make conventional synaptic contacts onto bipolar terminals, other amacrine processes, amacrine cell bodies, ganglion cell dendrites and bodies. Amacrine cells possess dense-core vesicles. Ganglion cells are never presynaptic elements. Serial synapses between amacrine processes and reciprocal synapses between amacrine processes and bipolar terminals are described. The inner plexiform layer contains a large number of myelinated fibers which terminate near the layer of amacrine cells.This work was supported by an N.I.H. grant NB 05404-05 and a Fight for Sight grant G-396 to P.W. and N.I.H. grant NB 05336 to J.E.D. The authors wish to thank Mrs. P. Sheppard and Miss B. Hecker for able technical assistance. P.W. is grateful to Dr. G. K. Smelser, Department of Ophthalmology, Columbia University, for the use of his electron microscope facilities.     

The fine structure of blattarian prothoracic glands

Summary The ultrastructural characterization of the prothoracic glands derives interest from the fact that they are the only known source of a steroid hormone (ecdysone) among invertebrates. The present material includes nymphal glands of two blattarian species studied at graded intervals over a period of several intermolt cycles.Among the prominent cytological features of this organ are long and intricately interwoven cellular processes that may be separated from each other by extracellular channels with an average width of 0.5 . The plasma membranes of the cells facing these spaces are coated by an external lamina (boundary membrane) representing extensions of the same extracellular material that provides the connective tissue sheath of this and other insect organs. Micropinocytotic caveolae and vesicles present along this large cellular surface area may facilitate the transport of material between glandular cells and hemolymph, or vice versa.The cytoplasm contains a fairly moderate amount of membranous structures. Golgi units are distinctive but never spectacular; ergastoplasmic elements are sparse in most cells. This sparsity as well as the absence of membrane-bounded secretory granules is in line with the known steroidal nature of the secretory product involved. Some cells show a striking array of microtubules.Certain structural attributes of nucleoli, mitochondria, and lysosome-like bodies seem to vary in conjunction with distinct phases of the intermolt cycle.Dedicated to an inspiring teacher and loyal friend, Professor F. Wassermann on the occasion of his 80th birthday, August 13, 1964. — Supported by Research Grants AM-03984 and NB-02145 from the U.S.P.H.S. — I wish to thank Mrs. Cynthia Jones and Mr. Stanley Brown for their skillful assistance.     

Fine structure of the retina in Haliotis discus

Summary The fine structure of the retina of Haliotis discus has been studied by means of electron microscopy. The visual cell has an apical projection which protrudes beyond the retinal surface into the ocellar cavity. The surface of this projection shows elaborate in- and outfoldings. Besides, two apposed laminae of the folded plasma membrane contact each other to form a quintuple-layered compound membrane. The analogy of this compound membrane system to the rhabdomere of the visual cell of Cephalopoda has been discussed. Subsurface endoplasmic reticulum and giant multivesicular bodies are also notable structures in Haliotis visual cells. The observations include the fine structure of supporting cells, plexiform layer, optic nerve and transitional zone of retina to epidermis.The author wishes to express his appreciation for the encouragement and suggestions given by Dr. Toshi Yuki Yamamoto, Professor of Anatomy, Tohoku University School of Medicine, through all stages of this work.     

Fine structure of the epithelial reticular cells of the medulla of the thymus in the golden hamster

Summary The epithelial reticular cells of the thymic medulla of the golden hamster were studied by electron microscopy. On the basis of their structural details two cell types are distinguished, although the two types are similar in basic structure. The cells of one type are more extended in shape and darker in appearance. They are connected with one another by their cytoplasmic processes, forming a reticulum in the medulla. Thus they appear to play a supporting role as do the cortical epithelial reticular cells. The other cell type is larger, more rounded and lighter. The characteristic feature of this cell type is an abundance of vesicular structures, which occur as vesicles or vacuoles of varying sizes. In addition, an enormous, intracytoplasmic ciliated cyst is occasionally encountered in the latter cell type. The cyst may be regarded as representing a specialized form of the vesicular structures. The possible functional significance of the latter cell type is discussed in relation to recent concepts concerning the mechanism of thymic function.Dedicated to Professor W. Bargmann, under whose guidance my thymus studies were begun, in honor of his 60th birthday (T. Ito).     

Photoperiodic and osmotic influences on the ultrastructure of the hypothalamic neurosecretory system of the White-crowned sparrow,Zonotrichia leucophrys gambelii

Summary An attempt was made to correlate functional changes in the neurohypophysis of the White-crowned Sparrow, Zonotrichia leucophrys gambelii, with morphologic features on the light- and electron-microscope levels. The aldehyde-fuchsin-staining anterior median eminence possesses essentially the same ultrastructural features as the non-staining posterior median eminence. The axon terminals are characterized by the presence of a large number of small vesicles (approximately 400 Å in diameter) and occasional electron-dense granules. The more-or-less depleted anterior median eminence occasionally evident in the photosensitive bird showing testicular development is indistinguishable ultrastructurally from the more intensely staining median eminence generally characteristic of the photorefractory bird. In the median eminence, stainability and functional state do not seem to be correlated with changes in the type, size or number of vesicles. A slight increase in the number of granules was noted in the photorefractory bird but this was considered insufficient basis to account for differences in stainability.The pars nervosa, on the other hand, responded to osmotic stimuli (saline drinking water) by loss of stainability and decrease in numbers of elementary neurosecretory granules. Small vesicles are also present in the pars nervosa axon terminals, but are intermingled with neurosecretory granules in normal birds. Acute-osmotic birds, however, had axon terminals almost entirely occupied by small vesicles.It is to be emphasized that the pars nervosa and the median eminence are two structurally very different regions of the neurohypophysis. The basis for aldehyde-fuchsin staining in the median eminence appears to differ from that in the pars nervosa. The implications of these findings are considered in regard to hypothalamic control over gonadotropic activity in the White-crowned Sparrow.Dedicated to Professor Dr. W. Bargmann in honor of his 60th birthday.This investigation was supported by grant GB-2484 from the National Science Foundation to Professor Bern, grant GB-2819 from the National Science Foundation to Professor Mewaldt, and grant NB-01353 from the National Institutes of Health to Professor Farner. The authors wish to express their appreciation of the technical assistance of Mrs. Irene Brown, Mr. John Butchart, Sally S. Kibby, Mrs. Carol Nicoll, and Mr. John Striffler. Mrs. Emily Reid kindly prepared the histograms.     

Ultrastructure of the neurohaemal region of the toad median eminence

Summary According to the internal structure and size of the granules, six types of nerve endings can be distinguished in the toad median eminence: 1. Endings containing mostly dense granules of 600 Å in diameter; 2. Endings containing dense granules of about 800 Å in diameter; 3. Endings which contain dense granules 1,000–2,000 Å in diameter, with the peak at 1,200–1,400 Å; 4. Endings containing granules with a characteristic structure, which differentiate them from the other three types; 5. Scarce endings containing granules 2,000 to 3,800 Å in diameter; and 6. Endings containing only vesicles 400–500 Å in diameter. Types 3 and 4 endings are mainly found in the outer pericapillary zone, and are probably responsible for the strong Gomori-positive reaction observed in this zone. The other four types of endings occur mainly in the inner pericapillary zone, and appear to be Gomori-negative.The probable origins of the different types of endings, and their possible relations with the different releasing factors is discussed.The subendothelial basement membrane has numerous long processes which form a complicated network in contact with all the nerve endings, some nerve fibres and glial cells.Two types of glial cells are described. Pinocytotic vesicles are frequently seen at the points where these cells contact the basement membrane. All the ultrastructural features suggest that these cells are carrying out transport functions.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.The author is very grateful to Professor H. Heller for his continued encouragement and criticism and to Mr. J. Lane and Mr. P. Heap for their valuable help.     

Electron microscopic studies on the pars intermedia of the ferret

Summary The structure of the pars intermedia of the ferret has been studied with the electron microscope, with particular reference to the morphology of the glandular cells and their innervation. Two types of cell were found. The predominant cell is ovoid in shape and contains membrane-bound vesicles of varying size (1,000–5,000 Å) and density, the most electron-dense of which are associated with the Golgi region. The nucleus is indented and the cytoplasm contains rough endoplasmic reticulum. The second cell type is often associated with the colloid material and is elongated or stellate-shaped with long processes which extend between the predominant cells. It is devoid of cytoplasmic vesicles and has a poorly defined Golgi apparatus. Certain other structural features of this cell such as microvilli, cilia or cytoplasmic microfilaments are reminiscent of ependymal cells.Numerous nerve endings are observed throughout the pars intermedia, making synaptic contact with the predominant cell type. The majority contain vesicles with an electron-dense core measuring 750 Å; less frequently terminals contain dense granules measuring 1,000 A or more. Both also contain small electron-lucent vesicles (200–400 Å); occasionally terminals containing only the latter type are found. The pattern of innervation in the ferret is thus comparable to that previously observed in the cat, rather than that seen in rodents or monkeys, and the implications of this finding are discussed.We are indebted to Prof. Sir Solly Zuckerman, O. M., K. C. B., F. R. S., for his help and guidance and to Mr. J. Wallington for his unfailing technical assistance.     

A cytochemical method for fixation and staining of lipids in frozen-dried mouse pancreas for study with light and electron microscopes

Summary A method is described for the cytochemical identification of lipids in acinar cells of the pancreas based chiefly on reactions of their carboxyl ester linkages and their double bonds. The method involves the reaction in vacuo of certain amine and hydrazine vapors with lipids in the solid state. The method is useful for studies with the light and electron microscopes.This research was supported in part by grants from the Public Health Service (GM 08328) and the Commonwealth Fund.I have been guided throughout by the perceptive advice of Professor Herbert S. Anker, Department of Biochemistry, University of Chicago. I am indebted also to the tireless work and support of Mrs. Faustina Manelis and Mrs. Elizabeth Vilkas.Dedicated to Professor Friedrich Wassermann with admiration and affection on the occasion of his eightieth birthday.     

Intracellular compartmentation of two enzymes of berberine biosynthesis in plant cell cultures

Out of the eight enzymes involved in the biosynthesis of the isoquinoline alkaloid berberine, at least, two enzymes, berberine bridge enzyme and (S)-tetrahydroprotoberberine oxidase, are exclusively located in a vesicle with a specific gravity of =1.14 g·cm^–3 as shown by direct enzymatic assay as well as immunoelectrophoresis. Electronmicroscopic examination of the enzyme-containing particulate preparation from Berberis wilsoniae var. subcaulialata cultured cells demonstrated that it is composed mainly of membranous vesicles. The protein composition of this preparation reveals the presence of only about 20 separable proteins, of which two major ones are berberine bridge enzyme and (S)-tetrahydroprotoberberine oxidase. Incubation of these vesicles with the substrate (S)-reticuline in the presence and absence of S-adenosyl-l-methionine leads to the formation of a red product which was identified as dehydroscoulerine. If the cytoplasmic enzyme S-adenosyl-l-methionine:(S)-scoulerine-9-O-methyltransferase is added to the vesicle preparation in the presence of (S)-reticuline and S-adenosyl-l-methionine, not dehydroscoulerine but columbamine, the immediate precursor of berberine is formed. Some of the quaternary alkaloids are located inside the vesicles; fusion of these vesicles leads to vacuoles containing the quaternary alkaloids. These vesicles are the first highly specific and unique compartment serving only alkaloid biosynthesis; they are found in members of four different plant families and in cell cultures as well as in differentiated tissue.Abbreviations BBE berberine bridge enzyme - STOX (S)-tetrahydroprotoberberine oxidase Dedicated to Professor Karl Decker, Freiburg, on the occasion of his 60^th birthday     

Origin of the Golgi system in amoebae

Summary An electron microscopic study of the Golgi apparatus in the giant amoeba, Pelomyxa illinoisensis, has been presented. Studies of normally feeding, dividing, starving, and refeeding amoebae were made. The major finding is that plasmalemma vesicles, formed via pinocytosis and phagocytosis, either flatten or invaginate and form the cisternae of the Golgi apparatus. Plasmalemma vesicles are also a source of new cisternae during the lifetime of a given Golgi apparatus. The cisternae migrate through the Golgi system, but before being released they either inflate, or segment into smaller vesicles. It is postulated that they later empty into the contractile vacuole and into certain other vacuoles. No evidence was found for the fusion of smooth Golgi vesicles or fringed vesicles of any kind with the plasmalemma.Dedicated to Professor Friedrich Wassermann with admiration and affection on the occasion of his eightieth birthday.Work supported by U. S. Atomic Energy Commission. A part of the work was reported at the XVI International Congress of Zoology, Washington, D. C., in 1963.     

Fine structure of the Paraventricular organ of Xenopus laevis tadpoles

Summary The ultrastructure of the Paraventricular organ in the hypothalamus of Xenopus laevis tadpoles is described. It appeares that the Paraventricular organ of this anuran species is homologous with the Organon vasculosum hypothalami or the Paraventricular organ of other vertebrates.The Paraventricular organ of Xenopus laevis is characterized by an ependymal lining with only few cilia and by two types of nerve cells. Both types of nerve cells have ventricular processes, protruding into the lumen of the third ventricle and forming a network. The protrusions bear cilia of the 8+1 pattern. It has been possible to distinguish both types of nerve cells on account of their dense-core vesicles. A secretory function of both cell types is suggested.In a region close to the Paraventricular organ, another granulated type of nerve cell has been observed. A relationship between these cells and the preoptic nucleus is discussed.The author thanks Prof. Dr. P. G. W. J. van Oordt for his helpful comments and criticism, Mr. H. van Kooten for photographic assistance and Mr. F. Dijk for technical assistance.     

A possible correlation between ultrastructure and function in the thin descending and ascending limbs of the loop of Henle of rabbit kidney

Summary An ultrastructural study of the thin loops of Henle has been made in the renal papilla of the rabbit. Animals in different states of water balance were used but no morphological difference was observed in the loops obtained from animals in different experimental groupings. The cytoplasm of the squamous cells lining the limbs was characterised by a paucity of organelles. Descending and ascending limbs were distinguishable. A distinct morphological difference was seen in the junctional regions of cell processes of the descending and ascending thin limbs of the loop. The ascending limb processes were joined by continuous tight junctions whereas the descending limb junctional regions invariably showed a space of at least 70 Å between adjacent processes. It is suggested that there may be a correlation between the structure of these junctional regions and the different permeability characteristics of the two limbs. The thin ascending limb must, on physiological evidence, be relatively impermeable with reference to the thin descending limb.The author wishes to thank Professor F. R. Johnson for his advice and assistance, and Mr. R. F. Birchenough, Mr. P. L. Hyam and Mr. J. Manston for valuable technical assistance.     

On the alleged presence of non-argyrophile argentaffin cells in the human gastro-intestinal tract

Summary The relationship between the argentaffin and argyrophile cells of the human gastrointestinal tract has been studied, in foetal and adult material, by a technique involving the staining of sections first by an argentaffin method (Gomori-hexamine silver, Schmorl, Diazonium) and subsequently by an argyrophile method (Bodian). A comparison of the cells staining by the two methods shows that all argentaffin cells of the human gastrointestinal tract are also argyrophile and that there is no evidence to support the claim of Hellweg (1952) and of HamPerl (1952) regarding the presence of non-argyrophile argentaffin cells.W. H. O. fellow from the Department of Anatomy, Medical College, Rohtak, India. — I am very grateful to Professor J. D. Boyd and to the World Health Organisation for having made it possible for me to carry out this research at the Anatomy School, Cambridge. I am indebted to Dr. G. A. Gresham and his staff for their very willing cooperation in providing material from surgical resections. My thanks are also due to Mr. J. F. Crane for the photographs and to Mr. J. W. Cash and Mr. R. Smith for helpful discussions on staining techniques.     

The reticular substance of the medulla oblongata of the albino rat

Summary The region of the reticular giganto-cellular nucleus, perfused with formalin and postfixed in osmium tetroxide, was studied with histochemical and electron microscopic techniques. The perikarya of the neurons have two zones. The peripheral cytoplasm contains Nissl bodies, mitochondria, and free RNP particles. The juxtanuclear cytoplasm contains the Golgi complex, mitochondria, RNP particles and dense bodies. The nucleus is indented and has a prominent nucleolus and a paranucleolar body. Dense bodies are found along the axon and dendrites as well. Three different types of synapses are described and two types of synaptic vesicles (spherical and ellipsoidal) are shown.The capillary endothelium shows microvilli and marginal flaps. The endothelial cytoplasm contains vacuoles, micropinocytotic vesicles, and a few dense bodies. Processes of pericapillary cells, surrounded by a basement membrane, also contain dense bodies. The dense bodies found in the neurons and endothelial cells show acid phosphatase activity. On the basis of their morphology and their enzymatic activity these bodies are identified as lysosomes.Partially supported by a school grant No RF 62051 from the Rockefeller Foundation, New York, USA, and Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.Fellows of the Consejo National de Investigaciones Científicas y Técnicas, Argentina. The authors wish to thank Dr. Mario H. Burgos for his constant interest and criticism, and to Dr. Eduardo Rodriguez Echandia and Dr. Fabio L. Sacerdote for their valuable assistance.     

The fine structure of the megakaryocyte of the bone marrow of the guinea pig

Summary The cytoplasm of megakaryocytes frequently exhibits bullate processes which protrude into the lumen of the sinusoids through small apertures in the reticular cells. These bullae differ morphologically from the platelet demarcation zones and are held to have a different function. It is concluded that the bullae detach from the megakaryocyte in a manner comparable to apocrine secretion and enter the blood stream.This investigation was supported by a PHS research grant (CA 05493) from the U.S. Public Health Service.Dedicated to Professor Friedrich Wassermann with admiration and affection on the occasion of his 80^th birthday.     

The evidence for a meiotic process in the euglenineae

Summary Cells of Hyalophacus ocellatus are described which contain either a nuclear figure consisting of a double complement of highly condensed chromosomes arranged in pairs in the anterior half of the cell, or a huge posteriorly-placed nucleus consisting of long granular chromosomes which also show signs of pairing. These nuclear figures are quite unlike interphase nuclei or stages in mitosis and are thought to be stages in euglenoid meiosis.No evidence has been obtained for a sexual fusion of gametes or cells. Previous accounts of sexuality and autogamy in the Euglenineae are historically reviewed and critically discussed relative to the present observations.This paper is dedicated to Professor Dr. E. G. Pringsheim on the occasion of his 80th birthday, with gratitude both for his untiring advice on my research and for his friendship.