Absorption of ferritin by cells of the digestive gland in Nassarius tegula (Gastropoda : Prosobranchia)

Within 12 min after the prosobranch snail, Nassarius, begins feeding on ferritin-labeled food, ferritin reaches the lumen of the digestive gland and is absorbed by the digestive cells lining the gland. Within the digestive cells, the ferritin is present in coated pinocytotic vesicles, in microvesicles and in macrovesicles. It is probable that ferritin (and components of the food as well) progresses rapidly in order from the gland lumen to the pinocytotic vesicles to the microvesicles to the macrovesicles. The macro vesicles are presumably an important site of intracellular digestion.     

Nuclear membrane contributions to the Golgi complex

Summary Electron microscopic examination of a variety of rapidly growing or differentiating mammalian and avian cells suggests that many of the Golgi vesicles and saccules arise directly from the outer nuclear membrane. Evidence for this interpretation includes: (1) the presence of a continuum of vesicles which appears to originate from the outer nuclear membrane and to enlarge gradually into saccules in the region of the Golgi membrane complex; (2) the absence of ribosomes on the nuclear blebs and the vesicles formed in these regions along the nuclear envelope; (3) the presence of active nuclear vesiculation near the Golgi region in cells essentially devoid of rough and/or smooth endoplasmic reticulum, and (4) the demonstration of peroxidase activity in the cisternae of the nuclear envelope and in vesicles extending in rows from the nuclear envelope to the Golgi complex. Supported by Research Grants HE 04061-09 (HEM), C-5315 and 1S01 FR-05109-01, Project 10 from the National Institutes of Health, Bethesda, Maryland.     

The mystery of the unstained Golgi complex cisternae

The Champy-Maillet OsKI reaction has been used upon Golgi complexes to show two kinds of staining. It stains material being processed as it passes along the secretory pathway of the rough endoplasmic reticulum (RER) and Golgi cisternae (GC) up to crystallization in secretory vesicles. It also stains separately the environment within parts of the GC. This GC staining may occur in all compartments (transition vesicles, saccules, condensing vacuoles), but it is characteristically missing from any one of them. The unstained cisternae may be explained if outer saccules are made from either stained or unstained transition vesicles, both of which occur. The presence of empty, unstained transition vesicles is dictated by the surface to volume ratios of microvesicles in relation to saccules. Most transition vesicles must return their membrane to the endoplasmic reticulum, but from time to time it is presumed that they fuse to make a saccule. Saccules, stained and unstained, then mature through the stack. OsKI reactions with tissues and test molecules suggest that in the RER and GC the stain detects labile--S . S--bridges before they lock the tertiary configuration of proteins.     

Ultrastructure of Thraustochytrium sp. zoospores

Summary Acid phosphatase distribution in the biflagellate zoospores of a marine fungus Thraustochytrium, resembling T. motivum Goldstein, was examined utilizing ultrastructural cytochemistry. Acid phosphatase activity was found in the Golgi saccules, Golgi vesicles, multivesicular bodies, endoplasmic reticulum, and autophagic vacuoles.Extensive autolysis of cellular structures occurs in the zoospores. Organelles or portions of the cytoplasm are segregated from the rest of the cytoplasm by acid phosphatase-positive vesicles and lamellae. These vesicles and lamellae coalesce around a portion of cytoplasm forming an enclosing double membraned sac. One of the membranes, probably the inner, is disrupted, releasing the hydrolytic enzymes which initiate digestion of the enclosed cytoplasm. These cytolysomes eventually fuse with larger cytolysomes where digestion is presumably completed. The final fate of the digestive residues and the large cytolysomes has not been determined.Contribution No. 501, Virginia Institute of Marine Science, Gloucester Point, Virginia 23062, U.S.A.Supported in part by the Oceanographic Section, National Science Foundation, Grant # GA-31014, to Dr. Frank O. Perkins.     

Fine Structure of a Marine Ameba Associated with a Blue-Green Alga in the Sargasso Sea*,†

SYNOPSIS An ameba, bearing a fringe of scales on the plasmalemma surface, dwells among the filaments of the colonial, blue-green alga Trichodesmium thiebautii (Sournia), and preys upon bacteria growing within the colony. The cytoplasm is clearly differentiated into a fine fibrillar ectoplasm at the periphery of the cell and a central endoplasm containing most of the membranous organelles. The nucleus contains a spheroidal nucleolus which is centrally located, and a double membrane containing pores. The tubular mitochondria, microbodies, lysosomes, and endoplasmic reticulum are typical for protozoa. The Golgi apparatus consists of an array of elongate flattened cisternae. One surface is associated with a fine fibrillar layer and the opposite surface contains electron-dense vesicles (perhaps primary lysosomes) and scale-containing vesicles that appear to be the origin of the scales deposited on the plasma membrane. Three kinds of bacteria-containing vacuoles are presnt: (a) vacuoles surrounded by 3 membranes and containing bacteria that are either healthy or in an early stage of digestion, (b) singlemembrane vacuoles which are food vacuoles that become converted to digestive vacuoles, and (c) larger vacuoles resembling those in (b) which contain prey in an advanced stage of digestion. The presence of amebae within pelagic algal communities provides further evidence for the diversity of their habitats in the ocean.     

Intracellular transport of albumin through the secretory apparatus of rat liver parenchymal cells. An immunocytochemical study

The fine structural localization of albumin in rat liver parenchymal cells was determined by an improved immunocytochemical method and serial sectioning. Albumin in the secretory apparatus of the parenchymal cells was present in segments of the rough endoplasmic reticulum, interrupted with negative segments, in transport vesicles, Golgi saccules, finely anastomosed tubules and vesicles on the trans side of the Golgi complex, and in secretion granules. Horizontally sectioned Golgi saccules contained lipoprotein particles on one side and albumin on the other side. After transport, the vesicles that contained albumin fused with the so-called rigid lamellae on the trans-side of the Golgi complex. Ultrathin serial sections revealed no true structural continuity between the endoplasmic reticulum and the cis-aspect of the Golgi complex. We concluded that secretory proteins are transported from the endoplasmic reticulum to the Golgi complex by transport vesicles that bud from the endoplasmic reticulum and fuse with the Golgi saccules. These vesicles fuse regularly with the Golgi saccules on the cis-side and occasionally with tubular elements on the trans-aspect that may belong to the so-called GERL.     

Electron microscopy of the rumen ciliate Entodinium caudatum, with special reference to the engulfment of bacteria and other particulate matter

A study in the electron microscope of thin sections of the rumen ciliate Entodinium caudatum was undertaken in an attempt to elucidate the mode of engulfment of particulate matter. This protozoon engulfed bacteria, polystyrene latex particles and olive oil into membrane-lined vesicles in the protozoal endoplasm. Particles of palladium black were also taken up into the endoplasm, but due to the toxic nature of this material it was not possible to demonstrate vesicle formation with certainty. The initial uptake of bacteria may be into large sacs containing many organisms which were subsequently taken into the endoplasm in vesicles that contained only one bacterium each. The evidence obtained in this investigation has been used to distinguish between two different mechanisms for the digestion of bacteria and utilization of the amino acids from the bacterial protein for the synthesis of protozoal protein.     

Cytological and enzyme-histochemical investigations on the digestive organs of Nautilus pompilius (Cephalopoda, Tetrabranchiata)

The foregut, stomach, caecum, midgut, and rectum of the digestive tract of Nautilus pompilius L.were investigated with ultrastructural and enzyme-cytological methods. Three different cell types were identified within the lamina epithelialis mucosae: main cells, goblet cells, and cells with secretory granules. The main cell type is the epithelial cell with microvilli, a basal nucleus surrounded by dictyosomes, rough endoplasmic reticulum, mitochondria, and electron-dense granules identified as lysosomes in the apical part of the cell. In the caecum this cell type contains endosymbiotic bacteria. The presence of endocytotic vesicles and the storage of lipids in the caecum indicate that this organ is involved in the process of absorption. In the caecum and the longitudinal groove of the rectum the main cells are, in addition, ciliated, facilitating the transport of food particles and faeces. Two types of goblet cells are found in all organs except in the stomach, forming a gliding path for food particles and protecting the epithelium. In the foregut and rectum, cells with electron-dense granules were recognized as the third type. The conspicuous secretory cells of the rectum represent a delimited rectal gland; its possible biological function is discussed. The tunica muscularis in all organs of the digestive tract consists of obliquely striated muscle cells innervated by axons containing transparent, osmiophilic and dense-cored vesicles. Positive reactions for acid and alkaline phosphatase, monoamine oxidase, β-glucuronidase, and trypsin- and chymotrypsin-like enzymes are localized in the lamina epithelialis mucosae.     

Ultrastructure of the cytoplasm of the lower holotrichous infusorian Tracheloraphis prenanti]

The ciliature of T. prenanti Dragesco 1960 (forma oligocineta Raikov et Kovaleva, 1968) consists of 14-18 ventral and lateral longitudinal kineties with paired kinetosomes, carrying either two cilia or one cilium per kinetosome pair (in the latter case, the nonciliated kinetosome is always the posterior one). The ectoplasmic fibrillar system belongs to the postciliary type. A pair of kinetosomes shares a common basal plate. The anterior kinetosome gives rise to a short ribbon of transverse microtubules, the posterior one, to a poorly developed kinetodesmal filament and to a strong ribbon of postciliary microtubules. The latter proceeds backwards along 8 to 12 kinetosome pairs, being incorporated into a laminated postciliodesma which accompanies each kinety on its right side. Rows of Golgi elements, sending secretory vesicles and channels towards the body surface, exist beneath the kinetosome bases. Each kinety is accompanied on its left by a microfibrillar myoneme, surrounded by perimyary vesicles and underlain by a row of mitochondria. The median part of the dorsal surface is nonciliated; the cytoplasm here is rich of membrane systems, contains peripheral, electron-dense, extrusible inclusions and sometimes also bacteria. The electron-dense inclusions develop in the endoplasm, in close contact with mitochondria. The endoplasm contains also large microfibrillar spheres of unknown nature.     

Electron microscopic and cytochemical studies of the mouse subcommissural organ

Summary In mice most of the ependymal cells of the subcommissural organ (SCO cells) are densely packed with dilated cisternae of the endoplasmic reticulum (ER) containing either finely granular or flocculent materials. The well developed supra-nuclear Golgi apparatus consists of stacks of flattened saccules and small vesicles; the two or three outer Golgi saccules are moderately dilated and exhibit numerous fenestrations; occasional profiles suggesting the budding of coated vesicles and formation of membrane-bound dense bodies from the ends of the innermost Golgi saccules are seen. A few coated vesicles and membrane-bound dense bodies of various sizes and shapes are also found in the Golgi region.The contents of the dilated ER cisternae are stained with periodic acid-silver methenamine techniques. In the Golgi complex the two or three inner saccules are stained as deeply as the dense bodies, and the outer saccules are only slightly stained. The stained contents of ER cisternae are more electron opaque than those of the outer but less opaque than those of the inner Golgi saccules and the dense bodies.Acid phosphatase activities are localized in the dense bodies, some of the coated vesicles in the Golgi region, and in the one or two inner Golgi saccules.On the basis of these results the following conclusions have been reached: (1) In mouse SCO cells the finely granular and the flocculent materials in the lumen of ER cisternae contain a complex carbohydrate(s) which is secreted into the ventricle to form Reissner's fiber; (2) the secretory substance is assumed to be synthesized by the ER and stored in its cisternae, and the Golgi apparatus might play only a minor role, if any, in the elaboration of the secretory material; (3) most of the dense bodies in the mouse SCO cells are lysosomal in nature instead of being so-called dark secretory granules.Sponsored by the National Science Council, Republic of China.     

Light and electron microscopy studies of the oesophagus and crop epithelium in Aplysia depilans (Mollusca, Opisthobranchia)

The oesophagus and crop epithelium of Aplysia depilans consist in a single layer of columnar cells with apical microvilli, and some of them also possess cilia. Cell membrane invaginations, small vesicles, multivesicular bodies and many dense lysosomes were observed in the apical region of the cytoplasm. In most cells, a very large lipid droplet was observed above the nucleus and a smaller one was frequently found below the nucleus; glycogen granules are also present. Considering these ultrastructural features, it seems that these cells collect nutritive substances from the lumen by endocytosis, digest them in the apical lysosomes and store the resulting products. The cell bodies of mucus secreting flask-shaped cells are subepithelial in the oesophagus and intraepithelial in the crop. Histochemistry methods showed that the secretion stored in these cells contains acidic polysaccharides. Secretory vesicles with thin electron-dense filaments scattered in an electron-lucent background fill most of these cells, and the basal nucleus is surrounded by dilated rough endoplasmic reticulum cisternae containing small tubular structures. Considering the relatively low number of secretory cells, mucus production cannot be high. Moreover, since protein secreting cells were not observed in either oesophagus or crop, extracellular digestion in the lumen of these anterior segments of the digestive tract most probably depend on the enzymes secreted by the salivary and digestive glands.     

Electron microscopic studies on the pineal organ of the antarctic penguin, (Pygoscelis papua)

The pineal organ of the migratory antarctic penguin, Pygoscelis papua, has a lobular structure. Clusters formed by different types of parenchymal cells are separated by connective tissue septa containing blood vessels. The predominant cell type displays a well-developed Golgi complex, free ribosomes, clear and granular vesicles (secretory granules), and lysosomes. Other cell types found in the gland are supporting and ependymal-like cells. The former contain dense bodies and filament bundles, the latter possess abundant cilia and clusters of ribosomes. Typical photoreceptor elements are lacking. Blood vessels are located within a perivascular space bordered by basal laminae. This perivascular space extends between the basal protrusions of the parenchymal cells. The presence of pinocytotic vesicles, secretory granules and cytoplasmic processes in the vicinity of these spaces suggests active sites of transport and exchange of substances. Intercellular conaliculi-like spaces are surrounded by parenchymal cells rich in microvilli. These cancliculi are continuous with the cavities (invaginations) of secretory and other parenchymal cells.     

Tridimensional structure of the Golgi apparatus in type A ganglion cells of the rat

The three-dimensional structure of the whole Golgi apparatus and of its components in type A ganglion cells was examined in thin and thick sections by low- and high-voltage electron microscopy. At low magnification, in 10-micron-thick sections of osmicated cells, the Golgi apparatus formed a broad, continuous perinuclear network. At higher magnification and in thinner sections of cells impregnated with uranyl acetate-lead-copper citrate or postfixed in K-ferrocyanide-reduced osmium, the Golgi apparatus appeared as a heterogeneous structure in which saccular regions characterized by stacks of saccules alternated with intersaccular regions made up of branching membranous tubules which bridged the saccules of adjacent stacks. The saccular regions consisted of the following superimposed elements: a cis-osmiophilic element made up of anastomosing tubules; two or three saccules negative for the phosphatases tested (i.e., nicotinamide adenine dinucleotide phosphatase = NADPase, thiamine pyrophosphatase = TPPase, and cytidine monophosphatase = CMPase); two saccules showing TPPase activity; and one to three trans-sacculotubular elements showing a "peeling-off" configuration, one of which showed CMPase activity. The saccules (phosphatase-negative) on the cis-side of the Golgi stacks showed, in addition to small circular pores, larger perforations in register. The cavities thus formed in the stacks of saccules, called "wells," always associated with small 80-nm vesicles, had a pan shape with the mouth directed toward the cis-face and the bottom closed by a TPPase-positive saccule. In face views of the saccules, the smallest of these perforations showed either a crescent shape, due to the presence of a bud on one side of the perforation, or a circular shape with a single small 80-nm vesicle in the center which was occasionally attached to the saccule by a filiform stalk. Such smaller cavities were considered as the precursors of the larger perforations and eventually of the wells. The small 80-nm vesicles seen in the small cavities or in the wells appeared to form in situ and possibly migrate toward the cisternae of endoplasmic reticulum seen proximal to the cis-face of the stack of saccules. Small 80-nm vesicles were also numerous in the intersaccular regions, along the lateral- and trans-aspects of the Golgi stacks, while larger, 150-to 300-nm vesicles, coated and uncoated, were seen only on the trans-face of the Golgi stacks in proximity to the trans-sacculotubular elements which appear to "peel off" from the Golgi stacks.     

Relationship between the golgi apparatus, gerl, and secretory granules in acinar cells of the rat exorbital lacrimal gland

The method of secretory granuleformation in the acinar cells of the rat exorbital lacrimal gland was studied by electron microscope morphological and cytochemical techniques. Immature secretory granules at the inner face of the Golgi apparatus were frequently attached to a narrow cisternal structure similar to GERL as described in neurons by Novikoff et al. (Novikoff, P. M., A. B. Novikoff, N. Quintana, and J.-J. Hauw. 1971. J. Cell Bio. 50:859-886). In the lacrimal gland. GERL was located adjacent to the inner Golgi saccule, or separated from it by a variable distance. Portions of GERL were often closely paralleled by modified cisternae of rough endoplasmic reticulum (RER), which lacked ribosomes on the surface adjacent to GERL. Diaminobenzidine reaction product of the secretory enzyme peroxidase was localized in the cisternae of the nuclear envelope, RER, peripheral Golgi vesicles, Golgi saccules, and immature and mature secretory granules. GERL was usually free of peroxidase reaction product or contained only a small amount. Thiamine pyrophosphatase reaction product was present in two to four inner Golgi saccules; occasionally, the innermost saccule was dilated and fenestrated, and contained less reaction product than the next adjacent saccule. Acid phosphatase (AcPase) reaction product was present in GERL, immature granules, and, rarely, in the innermost saccule, but not in the rest of the Golgi saccules. Thick sections of AcPase preparations viewed at 100 kV revealed that GERL consisted of cisternal, and fenestrated or tublular portions. The immature granules were attached to GERL by multiple connections to the tublular portions. These results suggest that, in the rat exorbital lacrimal gland, the Golgi saccules participate in the transport of secretory proteins, and that GERL is involved in the formation of secretory granules.     

THE STRUCTURE AND FORMATION OF PROTEIN GRANULES IN THE FAT BODY OF AN INSECT

In the larva of the butterfly Calpodes ethlius, the fat body begins to store protein in the form of granules at about 30 to 35 hours before pupation, at a time when the endocuticle is being resorbed. At least two sorts of granule can be distinguished. The first granules to arise are those within vesicles of the Golgi complex. These may increase in size by incorporating material from microvesicles at their surface and by coalescence with one another. Later, at about 10 hours before pupation, another sort of granule arises by the isolation of regions of the endoplasmic reticulum (ER) within paired membranes derived from Golgi vesicles. Several of these ER isolation bodies coalesce, with fusion of their outer isolating membranes. The ribosomes and membranes may then disappear and the granules become indistinguishable from the protein granules formed from Golgi vesicles, or the ribosomes may remain and be embedded in dense crystalline protein, forming a storage body for both protein and RNA. Mitochondria are isolated within paired membranes in the same way as regions of the ER. The isolated mitochondria also coalesce in a similar manner. When the inner membranes are lost, the structure of a group of isolation bodies is indistinguishable from that of a cytolysome. Isolation within paired membranes, as described here, may be of general importance in segregating regions of massive lysis or massive sequestration.     

黑水虻消化道形态及组织结构的观察

本文比较了不同发育阶段黑水虻Hermetia illucens消化道的形态学差异,掌握了幼虫消化系统的组织学特征。利用体视镜观察黑水虻5龄幼虫、预蛹及成虫的消化道形态,利用光学显微镜和扫描电镜观察幼虫消化道各段(前肠、中肠、后肠)的显微及超微结构。结果表明：黑水虻幼虫及预蛹的消化道均由前肠(食道和前胃)、中肠及后肠组成,从幼虫到成虫,消化道的长度不断缩短。与幼虫和预蛹相比,成虫消化道形态变化明显,前胃消失,出现了嗉囊及胃盲囊,中肠进一步缩短,后肠分化为回肠、结肠和直肠。组织学观察结果显示,幼虫的唾液腺开口于口腔,由膨大的管状腺体和腺管组成。食道由特化为角质刺突的内膜层及发达的肌层组成,其末端延伸至前胃。前胃膨大为球状,包括三层组织结构。根据上皮细胞形态的差异,中肠可分为四个区段。后肠薄,肠腔内褶丰富,肠壁可见数量较多的杆状细菌。马氏管开口于中、后肠交界处,包括4支盲管,管内壁密布微绒毛。黑水虻消化道形态随发育阶段的变化,反映了各阶段摄食及消化生理的差异。幼虫消化道各段具有各自典型的组织学特征,其前、中、后肠可能分别承担了食物接纳与初步消化、消化与吸收以及重吸收功能。本研究结果为进一步了...     

The structure of the Golgi apparatus: a sperm’s eye view in principal epithelial cells of the rat epididymis

 The Golgi apparatus of epididymal principal cells shares many structural features with other cell types. Saccular regions are arranged in a cis-Golgi network, eight flattened saccules, and several trans-Golgi networks (TGNs). Dilated tubules form intersaccular connecting regions which joint together saccules at the same or different levels between adjacent stacks. Wells exist as large perforations in register with the four cis-most saccules and serve as areas of vesicular interactions. TGNs are variable and can appear to peel off the stack or to be detached from it in the form of an anastomotic tubular network with pale dilated areas corresponding to prosecretory granules connected by short narrow bridges. Elongated or discoid dilated cisternae of endoplasmic reticulum (ER) (sparsely granulated) lie over the cis face of the stack, from which they are separated by an intermediate compartment filled with vesicles and tubules. The ER is also closely juxtaposed to the TGNs and the eighth saccule but interconnections are never seen between them. Vesicles of the COP variety reside at all levels of the stack and appear to bud off the cis-located ER and the edges of the saccules, while clathrin-coated vesicles appear mainly on the trans face of the stack and next to lysosomes. In the supranuclear cytoplasm, clusters of vesicles and tubules, at times budding off enveloping ER, appear to radiate toward the Golgi stacks where they fuse with cis Golgi elements. Taken together, these observations suggest dynamic functions and interactions for the various Golgi elements, associated vesicles, ER, and vesicular tubular clusters. Accepted: 29 January 1998     

Secretory organelles in ECL cells of the rat stomach: an immunohistochemical and electron-microscopic study

ECL cells are numerous in the rat stomach. They produce and store histamine and chromogranin-A (CGA)-derived peptides such as pancreastatin and respond to gastrin with secretion of these products. Numerous electron-lucent vesicles of varying size and a few small, dense-cored granules are found in the cytoplasm. Using confocal and electron microscopy, we examined these organelles and their metamorphosis as they underwent intracellular transport from the Golgi area to the cell periphery. ECL-cell histamine was found to occur in both cytosol and secretory vesicles. Histidine decarboxylase, the histamine-forming enzyme, was in the cytosol, while pancreastatin (and possibly other peptide products) was confined to the dense cores of granules and secretory vesicles. Dense-cored granules and small, clear microvesicles were more numerous in the Golgi area than in the docking zone, i.e. close to the plasma membrane. Secretory vesicles were numerous in both Golgi area and docking zone, where they were sometimes seen to be attached to the plasma membrane. Upon acute gastrin stimulation, histamine was mobilized and the compartment size (volume density) of secretory vesicles in the docking zone was decreased, while the compartment size of microvesicles was increased. Based on these findings, we propose the following life cycle of secretory organelles in ECL cells: small, electron-lucent microvesicles (pro-granules) bud off the trans Golgi network, carrying proteins and secretory peptide precursors (such as CGA and an anticipated prohormone). They are transformed into dense-cored granules (approximate profile diameter 100 nm) while still in the trans Golgi area. Pro-granules and granules accumulate histamine, which leads to their metamorphosis into dense-cored secretory vesicles. In the Golgi area the secretory vesicles have an approximate profile diameter of 150 nm. By the time they reach their destination in the docking zone, their profile diameter is between 200 and 500 nm. Exocytosis is coupled with endocytosis (membrane retrieval), and microvesicles in the docking zone are likely to represent membrane retrieval vesicles (endocytotic vesicles).     

The spermiogenesis and the early spermatozoa of <Emphasis Type="Italic">Armorloricus elegans</Emphasis> (Loricifera,Nanaloricidae)

The spermiogenesis consisting of five spermatid stages and the early spermatozoon has been investigated in Armorloricus elegans (Loricifera) with the use of transmission electron microscopy. The male reproductive system consists of three parts; testes, vasa deferentia and seminal vesicles. Caudally, the two seminal vesicles merge together in a ciliated duct and the excretory/gonadal—and digestive systems continue through the recto-urogenital canal, which opens via the lateral gonopores and the temporarily closed anal system. Spermiogenesis mainly occurs in the testes, whereas further maturation of the late spermatids and early spermatozoa occurs in the vasa deferentia and seminal vesicles. A maturation gradient (from spermatocytes to spermatozoa) is found from the posterior peripheral part of the testes to the anterior periphery and then centrally. During spermiogenesis the round nucleus becomes more osmiophilic and condensation of chromatin occurs. Later the nucleus elongates until it becomes rod-shaped in the early spermatozoa. In the second spermatid stage, a large vesicle is formed by saccules developed from the Golgi complex. This vesicle develops further and consists of three different osmiophilic parts with some crystal-like structures inside and is on the outside almost entirely surrounded by thick striated filaments. In the mid-piece the flagellum has a typical 9 × 2 + 2 axoneme and the two mitochondria are fused into a single sheet surrounding the flagellum. In the early spermatozoon stage an acrosomal-like cap structure with an acrosome filament appears proximal to the protruded rod-shaped nucleus. This cap is not formed by the Golgi complex and therefore might not be a true acrosome. Comparing the early spermatozoa of A. elegans with other cycloneuralians has shown some similarities with especially Kinorhyncha and Priapulida. These similarities are thought to be plesiomorphic.     

The fine structure of the midgut in the mite Anystis baccarum (L.) (Acari, Actinedida: Anystidae)

The ventriculus and the midgut caeca of the fed females of Anystis baccarum (L.) were investigated by using light and electron microscopy. In addition to the main type of polyfunctional digestive cells, special secretory cells were detected in the anterior region of the ventriculus. The shape and the ultrastructure of the digestive cells vary depending on their physiological state. Intracellular digestion, absorption or excretion processes prevail at different stages of the cell cycle. The secretory cells are characterized by the presence of extensive rough endoplasmic reticulum, filling whole space of the cell. These cells do not contain the apical network of pinocytotic canals, which are typical for the digestive cells. Three types of secretory granules were found in the cytoplasm of the secretory cells that probably correspond to three sequential stages of granulogenesis. The primary secretory granules are formed by the fusion of Golgi vesicles. The primary granules fuse to form complex vesicles with heterogeneous contents. These secondary granules aggregate to form very large inclusions of high electron density (tertiary secretory granules), which probably represent the storage of the secretory product. All types of secretory granules were observed close to the apical plasmalemma.