An Ultrastructural Study of the Hemocytes of the Pericardial Body in the Ascidian Ciona intestinalis (L.)

Abstract The hemocytes of the pericardial body of Ciona intestinalis were studied by electron microscopy. Our findings showed that stem cells, clear vesicular granulocytes, microgranulocytes, unilocular granulocytes and globular granulocytes are present at the periphery of the smaller-sized pericardial bodies. The stem cells are small round cells with a large nucleus, with or without nucleolus, and homogeneous cytoplasm containing numerous ribosomes. The clear vesicular granulocytes are characterized by an ameboid shape and cytoplasm containing several large electron-lucent vacuoles and small electron-dense granules. The microgranulocytes are variable in shape and contain numerous large electron-dense granules. The unilocular granulocytes show a single large vacuole with an electron-dense or electron-lucent content and a thin layer of peripheral cytoplasm that contains the flattened nucleus. The globular granulocytes are characterized by the presence of large vacuoles containing either fibrogranular material or electron-dense aggregates.     

Spermatological characters of the pseudophyllidean cestode Bothriocephalus scorpii (Müller, 1776)

Spermiogenesis of Bothriocephalus scorpii (Cestoda, Pseudophyllidea) includes an orthogonal development of two flagella, followed by a flagellar rotation and a proximo-distal fusion with the median cytoplasmic process. The fusion occurs at the level of four attachment zones. The presence of dense material in the apical region of the differentiation zone in the early stage of spermiogenesis appears to be a characteristic feature for the Pseudophyllidea. The mature spermatozoon possesses two axonemes of 9+"1" pattern of the Trepaxonemata, nucleus, cortical microtubules, electron-dense granules and crested body. The anterior part of the gamete exhibits a centriole surrounded by electron-dense tubular structures arranged as incomplete spiral. When the crested body disappears, the electron-dense tubular structures are arranged into a ring encircling the axoneme. The electron-dense tubular structures and their arrangement appear to be a specific feature for the clade "Bothriocephalidea". The organization of the posterior extremity of the gamete with the nucleus is described for the first time in the Pseudophyllidea.     

The postbranchial digestive tract of the ascidian, Polyandrocarpa misakiensis (Tunicata: Ascidiacea). 2. Stomach

The organization of the stomach in the compound styelid ascidian, Polyandrocarpa misakiensis, is described, and the morphology and cell types of the stomach is discussed from the phylogenetic viewpoint. The stomach is a sac-like organ whose wall is formed into longitudinal folds. The stomach consists of external and internal epithelium. The internal epithelium is simple columnar, except for the bottom of the folds. There are five cell types: absorptive cells, zymogenic cells, endocrine cells, ciliated mucous cells, and undifferentiated cells. The absorptive cells have numerous microvilli. The apical region of these cells is occupied by coated vesicles. The zymogenic cells have a conical outline and a few microvilli on their apical surfaces. There are secretory granules in the apical region of zymogenic cells. The endocrine cells have low cell height and electron-dense granules around the nucleus. Endocrine cells have one or two cilia and a few microvilli on the apical surfaces. The basolateral part of these cells often bulges into the adjoining cells. Immunoelectron microscopy revealed that some endocrine cells have serotonin-like immunoreactivity. The ciliated mucous cells are restricted to a single ventral groove. They have numerous microvilli and a few cilia on their apical surfaces. Moderately electron-dense granules are accumulated in the apical part of the ciliated mucous cells. Undifferentiated cells, filled with free ribosomes, form a pseudostratified epithelium in the base of each fold. The nucleus of undifferentiated cells has a prominent nucleolus. The pseudostratified epithelium of the pyloric caecum consists of electron-dense and electron-light cells.     

四种淡水养殖鱼类血细胞的细微结构

四种淡水鱼的血细胞形态基本相似。红血球形态与其他低等脊椎动物基本相似。淋巴球绝大部分是小淋巴球:单核球数量较少;四种鱼的嗜中性白血球形态结构差不多,胞核多为蚕豆形,很少见分叶核,分叶一般也只有二叶,这与哺乳类显然不同;嗜酸性白血球的形态结构与其他脊椎动物基本相似;在少数血涂片中看到了嗜碱性白血球。       

The formation of glandular secretion in larval Austramphilina elongata (Amphilinidea)

The ultrastructure of three types of gland cells of embryos and free-swimming larvae of Austramphilina elongata is described. Type I gland cells contain large, more or less round electron-dense granules which are formed by numerous Golgi complexes. Type II gland cells contain thread-like, membrane-bound secretory granules with longitudinally arranged microtubules inside the granules; secretory droplets are produced by Golgi complexes and the microtubules apparently condense in the cytoplasm or in the droplets. Type III gland cells contain irregular-ovoid membrane-bound granules with coiled up microtubules which have an electron-dense core; the granules are formed by secretionderived from Golgi complexes and the microtubules aggregate around and migrate into the secretion; microtubules are at first hollow and the early secretory granules have a central electron-dense region.     

The ultrastructure of the midgut epithelium in millipedes (Myriapoda,Diplopoda)

The midgut epithelia of the millipedes Polyxenus lagurus, Archispirostreptus gigas and Julus scandinavius were analyzed under light and transmission electron microscopies. In order to detect the proliferation of regenerative cells, labeling with BrdU and antibodies against phosphohistone H3 were employed. A tube-shaped midgut of three millipedes examined spreads along the entire length of the middle region of the body. The epithelium is composed of digestive, secretory and regenerative cells. The digestive cells are responsible for the accumulation of metals and the reserve material as well as the synthesis of substances, which are then secreted into the midgut lumen. The secretions are of three types – merocrine, apocrine and microapocrine. The oval or pear-like shaped secretory cells do not come into contact with the midgut lumen and represent the closed type of secretory cells. They possess many electron-dense granules (J. scandinavius) or electron-dense granules and electron-lucent vesicles (A. gigas, P. lagurus), which are accompanied by cisterns of the rough endoplasmic reticulum. The regenerative cells are distributed individually among the basal regions of the digestive cells. The proliferation and differentiation of regenerative cells into the digestive cells occurred in J. scandinavius and A. gigas, while these processes were not observed in P. lagurus. As a result of the mitotic division of regenerative cells, one of the newly formed cells fulfills the role of a regenerative cell, while the second one differentiates into a digestive cell. We concluded that regenerative cells play the role of unipotent midgut stem cells.     

鸭病毒性肠炎病毒强毒株的形态发生学与超微病理学研究

应用透射电镜和超薄切片技术,研究鸭病毒性肠炎病毒(duck enteritis virus,DEV)CH强毒株人工感染成年鸭后,病毒在宿主细胞内的形态发生及各组织器官的超微结构变化.结果表明,感染后不同时间剖杀及发病后死亡鸭的肝、肠、脾、胸腺、法氏囊等组织器官中,均观察到典型的疱疹病毒粒子.病毒主要的靶细胞为淋巴细胞、网状内皮细胞、成纤维细胞、巨噬细胞、血管内皮细胞、肠道上皮细胞、肠道平滑肌细胞和肝细胞等.DEV的核衣壳有空心型、致密核心型、双环型和内壁附有颗粒型四种形态,存在胞核和胞浆两种装配方式.病毒核衣壳可在核内获得皮层,通过核内膜获得囊膜成为成熟病毒;也可通过内外核膜进入胞浆,在其中获得皮层,然后在各种质膜上获得囊膜,最后成熟病毒释放到细胞外.伴随着病毒的复制、装配和成熟,细胞中出现多种核内和胞浆包涵体、核内致密病毒核酸颗粒、微管和中空短管以及胞浆内膜包裹的电子致密小体、双层管等病毒相关结构.超微研究表明,组织细胞有坏死和凋亡两种变化.坏死细胞肿胀甚至破裂,线粒体肿胀空泡化,粗面内质网扩张,核糖体脱落,有的细胞器甚至完全崩解,染色质或固缩或溶解.凋亡细胞则染色质聚集,胞浆凝聚深染,细胞膜上有大量空泡,并有凋亡小体形成.细胞坏死与凋亡往往同时存在,疾病发生过程中,脾、胸腺、法氏囊以及小肠固有层中的淋巴细胞凋亡数量明显增多.     

A Light and Electron Microscopic Study of Anabaena volzii Lemm

Anabaena volzii Lemm. is a rare species of Cyanophyta. It possesses characteristics of prokary0tes. Young filaments of A. volzii consist of only vegetative cells. The filament leng- thens by the increase of its cell number owing to amitosis. A mature filament contains vegetative cells, heterocysts and akinetes; the latter two differentiate from the vegetative cells. Vegetative cells and heterocysts are short-cylindric shaped. An akinete in longitudinal sections of appear to be elliptical. Viewed with a transmission electron microscope, an electron-dense cell wall, plasmolemma, thylakoids (photosynthetic lamellae), nucleo-plasmic region and polyhedral bodies can be seen in the vegetative cell. The nucleo-plasmic region, which lacks a nuclear envelope, is surrounded or dissected, but often connected with the thylakoids. There are also some extremely electron-dense (if samples were post-fixed in osmic acid) cyanophycin granules in its cytoplasm. Heterocyst is larger than vegetative cells. Its remarkable features are a thick envelope, an electron-transparent cell wall and a distinctive plug-like body at both ends of the cell respectively. In the plug-like body is seen an irregular narrow channel. Somewhat dilated thylakoids in the heterocyst appear to be more winding and contorted (than those in vegetative cells), making a dedicate pattern. A long ellipticring-shaped membrane structure is formed in a heterocyst ,composed, of an electron-dense rod core surrounded by 14 concentric layers of lamellae. Akinete forms thick cell wall. A nucleo-plasmic region, fine and contorted thylakoids, many cyanophycin granules, and abundant ribosomes are found in akinetes.     

The hypothalamic neurosecretory system of the marine teleost fish, Mugil auratus risso.

The hypothalamic neurosecretory system of the marinefish, Mugil auratus, consists of two nuclei, viz., the nucleus praeopticus and the nucleus laterlis tuberis. Both are paired, and while those of the nucleus praeopticus are vertically arranged as L-shaped bodies, their strand-like counterparts in the nucleus lateralis tuberis extend in an antero-posterior direction. The two constituent bodies of the nucleus praeopticus lie on both sides of the third cerebral ventricle. Each is differentiated into a dorsal pars magnocellularis and a ventral pars parvocellularis. A nervous tract, the hypothalamo-hypophysial tract, extends posteriorly from each body, but it is not until after they penetrate the pituitary gland that they fuse into one structure, the neurohypophysis. Many neurosecretory granules accumulate in the neurohypophysis adjacent to the meta-adenohypophysial region, and fewer scattered granules of varying sizes are also present along the hypothalamo-hypophysial tracts. Inner to these hypothalamo-hypophysial tracts extend the two bodies of the nucleus lateralis tuberis along the infundibular region. Axons from this nucleus extend sideways, and as they merge with those adjacently disposed of the hypothalamo-hypophysial tracts, they enter the pituitary gland as a unified structure.     

Electron microscopy of primary zoosporogenesis inPlasmodiophora brassicae

Primary zoosporogenesis in resting sporangia ofPlasmodiophora brassicae that had been incubated for 14 d in culture solution containing turnip seedlings was examined by transmission electron microscopy. A single zoospore differentiated within each sporangium, the differentiation being initiated by the emergence, of two flagella in the tight space formed by invagination of the plasma membrane within the sporangium. The differentiazing zoospore was similar in intracellular aspects to sporangia within clubroot galls. Then a deep groove formed on the zoospore cell body by further invagination of the plasma membrane. Two flagella appeared to coil around the zoospore cell body in parallel along this groove. Thereafter, the cell body lost the groove and became rounded following the protoplasmic condensation (contraction of cell body) during late development, and assumed an irregular shape at the stage of maturation. Intracellular features in, developing and mature zoospores were complicated, being characterized by electron-dense nuclei and mitochondria, microbodies, cored vesicles and various unidentified cytoplasmic vesicles and granules. A nucleolus-like region was observed only in the nucleus of the mature zoospore. A partially opened germ, pore was also seem in the sporangium containing the mature zoospore.     

Soft body reconstructions of Palaeozoic corals: implications for the system of Anthozoa (Coelenterata)

The soft bodies and individual developmental sequences of the polyps of Palaeozoic corals are reconstructed on the basis of the functional, engineering and constructional morphology of Recent Anthozoa. Four types of body construction can be distinguished by the arrangement of mesenteries, the number of mesentery insertion zones and characteristic septal insertion patterns: (1) serial insertion of single mesenteries in four sectors, which has resulted in the serial insertion of septa, (2) symmetrical insertion of single mesenteries in four sectors, which has resulted in a symmetrical septal pattern or pseudo radial septal patterns, (3) exponential insertion of paired mesenteries in four sectors, which has resulted in septa bifurcation, and (4) exponential insertion of paired mesenteries in six sectors, which has resulted in a radial septal pattern. Suggestions for a constructional taxonomy are given on the basis of the arrangement of mesenteries and on individual development of the reconstructed polyps. Accordingly, new superorders are introduced: 'Seriales' for the first body construction and 'Symmetricales' for the second. The third body construction is that of the Heterocorallia and the fourth that of the Hexacorallia. Following a constructional taxonomy, new and stricter definitions are given for the new and already known taxonomic categories of Rugosa, Heterocorallia and Hexacorallia. A byproduct of this re-definition is that several Palaeozoic corals represent the body construction of the Hexacorallia and should therefore be revised as Hexacorallia; consequently, Hexacorallia must already have been present in the Palaeozoic.     

Ultrastructural studies on the formation of yolk granules in the statoblast of a fresh-water bryozoan,Pectinatella gelatinosa

The formation of protein-carbohydrate yolk in the statoblast of a fresh-water bryozoan, Pectinatella gelatinosa, was studied by electron microscopy. Two types (I and II) of yolk cells were distinguished. The type I yolk cells are mononucleate and comprise a large majority of the yolk cells. The type II yolk cells are small in number; they become multinucleate by fusion of cells at an early stage of vitellogenesis. In both types of yolk cells, electron-dense granules (dense bodies) are formed in Golgi or condensing vacuoles, which are then called yolk granules. For the formation of yolk granules, the following processes are considered: 1. Yolk protein is synthesized in the rough-surfaced endoplasmic reticulum (RER) of the yolk cells. 2. The synthesized protein condenses in the cisternal space of the RER and is packaged into small oval swellings, which are then released from the RER as small vesicles (Golgi vesicles, 300-600 A in diameter). 3. The small vesicles fuse with one another to form condensing vacuoles, or with pre-existing growing yolk granules. 4. In the matrix of the condensing vacuoles or growing yolk granules, electron-dense fibers are fabricated and then arranged in a paracrystalline pattern to form the dense body. 5. After the dense body reaches its full size, excess membrane is removed and eventually the yolk granules come to mature. Toward the end of vitellogenesis of the yolk cells, the cytoplasmic organelles are ingested by autophagosomes derived from multivesicular bodies and disappear.     

Sperm ultrastructure of a member of the black coral family Aphanipathidae: Rhipidipathes reticulata (Anthozoa, Antipatharia)

Fertile male polyps of three colonies of the black coral Rhipidipathes reticulata (Aphanipathidae) from Togian Islands (Indonesia) have been the source of the sperm investigated at ultrastructural level, in order to compare their organization with that of other members belonging to the family Antipathidae and Myriopathidae. The extension of the studies to a representative of the family Aphanipathidae stresses once more the structural similarity of the male gametes in antipatharians. A sketch of the sperm model reports the similarity and differences in the examined taxa. Among the micro-characters, the cup-like body linked to the pericentriolar apparatus, is exclusive of the antipatharians. Other inclusions concern the more common pro-acrosomal vesicles or the acrosomelike structure observed only in Antipathella subpinnata and Myriopathes japonica. Lipid vesicles are occasionally present. A typical inclusion, the electron-dense content of which has a C-shaped configuration, is restricted to Rhipidipathes reticulata and is associated to the cup-like body or to the mitochondrion.     

Ultrastructure of the colon of Locusta migratoria

The ultrastructure of the colon of Locusta migratoria is described. The colon is lined by a thick cuticle that, for the most part, adheres to the underlying epithelium. The cuboid epithelial cells are characterized by moderate invaginations of the apical and, to a lesser extent, basal plasma membranes; the lateral plasma membranes are relatively flat. The bulk of the mitochondria are located in the apical region of the cell and are not particularly associated with any of the plasma membranes. The basal region of the cells contains much rough endoplasmic reticulum, glycogenlike granules, and a predominance of spherical, electron-dense bodies of various sizes. Where muscle fibers make contact with the epithelium, the cells are much reduced; the cytoplasm is usually less electron-dense, and, typically, the nucleus has a thick layer of granular material associated with the inner nuclear membrane. The apical and basal plasma membranes of the reduced epithelial cells contain numerous hemidesmosomes. The apical hemidesmosomes occur in pairs around an extracellular space that contains electron-opaque material. The latter forms tonofibrillae that extend into the endocuticle. Bundles of microtubules are associated with the hemidesmosomes. The tubules traverse the cell from the apical to the basal region. The possible significance of these findings is discussed.     

Zoosporulation in Labyrinthula sp.; an Electron Microscope Study1

SYNOPSIS. Zoosporulation in Labyrinthula sp. in monoxenic culture was initiated by aggregation of spindle cells into reticulate sori. The spindle cells then changed into rounded or oval cells and formed, de novo, 2 pairs of centrioles at opposite sides of each nucleus. A pair of granular aggregates (protocentrioles) ～ 240 mμ in diameter served as precursor bodies during centriole formation. Spindle microtubules around the prophase nucleus connected the pairs of centrioles but were not found in the nucleoplasm until nuclear envelope fragmentation occurred. Prophase nuclei of uninucleated sporangia contained synaptinemal complexes; therefore, meiosis is presumed to occur. The envelope fragments moved toward the centrioles and regrouped to form the nuclear membranes of the daughter cells. Alternating nuclear and cytoplasmic divisions subdivided the preparation into 8 cells which differentiated into laterally biflagellated zoospores. Flagellar development involved growth of the kinetosome microtubules into a bud which formed over the kinetosome tangential to the cell surface. Kinetosomes were derived directly from centrioles with little differentiation other than addition of an electron-dense core to the lumen of the centriole. Zoospore ultrastructure included a stigma comprised of a row of electron-dense granules located slightly under the plasmalemma and posterior to the pair of kinetosomes. A single row of 17–21 microtubules lay parallel to the stigma granules, one or more being connected to the anterior kinetosome. A striated fiber apparatus similar to that found in some phytoflagellates connected the midregions of the kinetosomes. Fibers 1.0–1.2 μ long were attached to the plasmalemma around the base of the anterior flagellum. Zoospores settled on the substrate and differentiated directly into spindle cells. Since synaptinemal complexes were observed the planonts are probably haploid zoospores and probably not gametes since planogametic copulation was not observed.     

The nuclei of cellular organelles and the formation of daughter organelles by the “plastid-dividing ring”

It has been established that organelles, such as mitochondria and plastids, contain organelle-specific DNA and arise from the division of pre-existing organelles (e.g., Possingham and Lawrence, 1983). We propose that organelle DNAs, such as mitochondrial DNA and plastid DNA are not naked in organellesin situ but are organized in each case to form an “organelle nucleus” with basic proteins (Kuroiwa, 1982). The concept of organelle nuclei has changed our ideas about the division of organelles. Thus, the process of organelle division must be composed of two main events: division of the organelle nucleus and organellekinesis (division of the other components of the mitochondrion or plastid). The latter term has been adopted as an appropriate analogue of cytokinesis. We were the first to identify the plastid-dividing ring (PD-ring), which is located in the cytoplasm close to the outer envelope membrane at the constricted isthmus of dividing chloroplasts in the red algaCyanidium caldirum. The PD-ring is about 60 nm in width and 25 nm in thickness, and is a circular bundle of actin-like, fine filaments, each about 4–5 nm in diameter. Since cytochalasin B, an inhibitor of polymerization of actin filaments, inhibits the formation of the PD-ring and, thus, prevents subsequent division of chloroplasts, the PD-ring is thought to be a structure that is essential for the division of plastids (plastidkinesis). The behavior of the PD-ring during a cycle of chloroplast division can be classified into the following four stages on the basis of morphological and temporal differences. The chloroplast growth stage: the small, spherical chloroplast increases in volume and becomes a football-like structure, while the PD-ring from the previous division disappears. Formation of the PD-ring: the somewhat electron-dense body (see below) is fragmented into many, somewhat electron-dense granules, which are aligned along the equatorial region of the chloroplast and fine filaments are formed from the somewhat electron-dense granules in the equatorial region. The fine filaments of the PD-ring align themselves according to the longest axis of their overall domain, i.e., circumferentially. Contraction stage: a bundle of fine filaments begins to contract and generates a deep furrow. Conversion stage: after chloroplast division, the remnants of the PD-ring are converted into somewhat electron-dense bodies. Similar events occur during the second cycle of chloroplast division. Since similar structures are observed extensively in the plastids of algae, moss and higher plants, the PD-ring appears to be an essential structure for the division of plastids in plants.     

Dorsal lingual epithelium of Platemys pallidipectoris (Pleurodira,Chelidae)

Scanning electron microscopy reveals that the flat tongue of Platemys pallidipectoris has shallow grooves and no lingual papillae. The surface of the tongue is covered with dome-shaped bulges, each corresponding to a single cell. Short microvilli are distributed over the cell surface. Light microscopy shows a stratified cuboidal epithelium with an underlying strong connective tissue. Transmission electron microscopy indicates four layers. The basal cells of the epithelium are electron-translucent and have a large central nucleus and a cytoplasm with keratin tonofilaments. Plasma cells with abundant rough endoplasmic reticulum and mitochondria occur in the basal layer. Production of secretory granules begins in the more electron-dense intermediate layers and increases as the cells move toward the surface. The membranes of the cells of the deep intermediate layer form processes that project into relatively wide intercellular spaces. In the superficial intermediate layer, the cytoplasm of the cells contains numerous fine granules; these increase in number but not in size in more distal layers. The cells of the surface layer are electron-translucent with a round nucleus. Contents of their fine granules are secreted into the oral cavity. © 1995 Wiley-Liss, Inc.     

Morphological Characterization of Three Phenotypes of the Isopod Armadillidium vulgare

The morphological characteristics and ommochrome quantity in the integument of red, white, and wild type (black-grey) Armadillidium vulgare were studied. The red phenotype was found to possess two kinds of immature ommochrome pigment granules within its pigment cells, in addition to mature pigment granules. The immature granules seemed to contain uniformly distributed fibrilles, or to have an electron-dense central region surrounded by an electron-lucent outer edge. Since these immature pigment granules were typically observed to be distributed along with the mature ones, and were also more easily extractable than the wild type's, it is hypothesized that ommochrome granule maturation in the red phenotype may occur slowly due to a defect in the pigment granule internal process which combines pigments with matrix proteins. Regarding the white phenotype, although its pigment cells were undeveloped, several large-sized vesicles containing a small amount of electron-dense material appeared in the pigment cell cytoplasm. The wild and red type males of A. vulgare were found to have an ommochrome content twice as large as that of the corresponding females, with no ommochrome pigment being detected in the white phenotype. The genetic relationship between the white and red phenotypes was discussed using as a basis the observed pigment granule structure.     

Ultrastructural observations on the granular leucocytes of the tuatara Sphenodon punctatus (gray)

The granular leucocytes of an active, mature female tuatara, Sphenodon punctatus (Gray) were examined in the electron microscope. Eosinophils contained a lobulated nucleus, homogeneous, dense, irregularly shaped granules, assorted smaller granular inclusions, mitochondria and beta-glycogen. Endoplasmic reticulum, Golgi complexes and ribosomes were scanty. Immature neutrophils (myelocytes) were regular in outline and contained a compact nucleus. In the adjacent centrosomal region were paired centrioles with connected microtubules, and Golgi complexes. Ovoid electron-dense granules, mitochondria, lipid droplets and numerous microfilaments arranged randomly or in bundles, lay in the cytoplasm. Mature neutrophils were often highly irregular in outline, had a segmented nucleus and contained possibly a second type of granular inclusion. The basophils were regular in outline with a compact nucleus. Numerous ovoid homogeneous, electron-dense granules, mitochondria, beta-glycogen particles and some microfilaments were seen in the cytoplasm. The granules in many basophils appeared 'altered' or degenerate and most of these contained microtubules. The cytology of the granulocytes of the tuatara is compared with that in other vertebrates.     

Ultrastructure of secretion in the atrial gland of a mollusc (Aplysia)

Extracts of the atrial gland of the sea hare Aplysia californiea (Mollusca) induce egg laying when injected into mature individuals. Since egg laying is controlled endogenously by a peptide secreted by neuroendocrine cells in the central nervous system, the relationship between the atrial gland and these central neurons has become an issue of interest. With the particular objective of examining secretory structures we undertook an ultrastructural study of the atrial gland and adjacent tissues. This study revealed that the atrial gland epithelium is composed of two major cell types: ‘goblet-like’ exocrine cells containing large electron-dense granules, and ciliated ‘capping cells’. A non-secretory, and possibly post-secretory, cell containing electron-lucent granules was noted. A region of the large hermaphroditic duct contiguous to the atrial gland, known as the red hemiduct, also displayed capping cells and secretory cells with large granules. The content of these granules is organized into crista-like condensations. The cell also contains iron-rich pigment inclusions.