Ultrastructural and cytochemical studies of the female gonad of Prorhynchus sp. (Platyhelminthes,Lecithoepitheliata)

The female gonad of Prorhynchus is heterocellular (neoophoran organization) and consists of an unpaired, elongate germovitellarium enveloped by a finely granular extracellular lamina. It is composed of a posterior germinative area where early oocytes are randomly associated with differentiating vitellocytes and a growth area with follicular organization. In each follicle a single oocyte is surrounded by a layer of vitellocytes. By electron microscopy, the oocytes showed features typical of non-vitellogenic germ cells; they had chromatoid bodies, annulate lamellae, lipid droplets and R.E.R. and Golgi complexes producing small granules with a multilamellar pattern. Vitellocytes showed features typical of secretory cells with the R.E.R. and Golgi complex developed to a great extent and involved in the production of type A and type B globules, respectively. We speculate that type A globules are shell-globules and type B globules are yolk. The structure, composition and role of vitellocyte globules of Prorhynchus are compared with those of homologous inclusions from other Platyhelminthes.Abbreviations A type A globule - B type B globule - ECL extracellular lamina - GC Golgi complex - L lipid - RER rough endoplasmic reticulum - O oocyte - V vitellocyte     

Ultrastructural and cytochemical aspects of the germarium and the vitellarium in Syndesmis patagonica (Platyhelminthes,Rhabdocoela, Umagillidae)

The cytoarchitecture of the female gonad of the endosymbiont umagillid Syndesmis patagonica has been investigated using electron microscopy and cytochemical techniques. The female gonad consists of paired germaria and vitellaria located behind the pharynx in the mid‐posterior region of the body. Both the germaria and the vitellaria are enveloped by an outer extracellular lamina and an inner sheath of accessory cells which contribute to the extracellular lamina. Oocyte maturation occurs completely during the prophase of the first meiotic division. Oocyte differentiation is characterized by the appearance of chromatoid bodies and the development of endoplasmic reticulum and Golgi complexes. These organelles appear to be involved in the production of round granules, about 2–2.5 μm in diameter, with a homogeneous electron‐dense core surrounded by a granular component and a translucent halo delimited by a membrane. These egg granules migrate to the periphery of mature oocytes, are positive to the cytochemical test for polyphenol detection, are unaffected by protease and have been interpreted as eggshell granules. The mature oocytes also contain a small number of yolk granules, lipid droplets, and glycogen particles scattered throughout the ooplasm. The vitellaria are branched organs composed of vitelline follicles with vitellocytes at different stages of maturation. Developing vitellocytes contain well‐developed rough endoplasmic reticulum and small Golgi complexes involved in the production of eggshell and yolk globules. Eggshell globules are round, measure 4–5 μm in diameter, and have a mosaic‐like patterned content which contains polyphenols. The yolk globules, 2–3 μm in diameter, show a homogeneous protein content of medium electron density, devoid of polyphenols, and completely digested by protease. The mature vitellocytes also contain glycogen as further reserve material. The presence of polyphenolic eggshell granules in the oocytes and of polyphenolic eggshell globules with a mosaic‐like pattern in the vitellocytes have been considered apomorphic features of the Rhabdocoela + Prolecithophora. J. Morphol. 275:703–719, 2014. © 2014 Wiley Periodicals, Inc.     

The female gonad in two species of Microplana (Platyhelminthes,Tricladida, Rhynchodemidae): Ultrastructural and cytochemical investigations

The female gonad of the land planarians Microplana scharffi and Microplana terrestris consists of two small germaria located ventrally in the anterior third of the body and of two ventro‐lateral rows of oblong vitelline follicles distributed between the intestinal pouches. Both these structures are enveloped by a tunica composed of an outer extracellular lamina and an inner sheath of accessory cells. Oocyte maturation is characterized by the appearance of chromatoid bodies and the development of endoplasmic reticulum and Golgi complexes. These organelles appear to be correlated with the production of egg granules with a fenestrated/granular content of medium electron density, about 4–5 μm in diameter, which remain dispersed in the ooplasm of mature oocytes. On the basis of cytochemical tests showing their glycoprotein composition, and their localization in mature oocytes, these egg granules have been interpreted as yolk. In the vitelline follicles, vitellocytes show the typical features of secretory cells with well‐developed rough endoplasmic reticulum and Golgi complexes involved in the production of eggshell globules and yolk. The eggshell globules, which appear to arise from repeated coalescences of two types of Golgi‐derived vesicles, contain polyphenols and, when completely mature, they measure about 1–1,2 μm in diameter and show a meandering/concentric content pattern as is typical of the situation observed in most Proseriata and Tricladida. Mature vitellocytes also contain a large amount of glycogen and lipids as further reserve material. On the basis of the ultrastructural features of the female gonad and in relation to the current literature the two species of rhynchodemids investigated appear to be closely related to the freshwater planarians belonging to the family Dugesiidae. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Ultrastructure of the female gonad of two temnocephalids (Platyhelminthes,Rhabdocoela)

The female gonad of Temnocephala dendyi and T. minor consists of a single germarium and two rows of vitellaria. It is enveloped by an extracellular lamina and accessory cells. Accessory cells are only peripherally located in the germarium while their cytoplasmic projections also fill the spaces between vitellocytes in the vitellarium. The main feature of oocyte maturation is the appearance of chromatoid bodies and the development of rough endoplasmic reticulum (R.E.R.) and Golgi complexes which appear to be correlated with the production of double-structured egg granules. The egg granules, which are localized in the cortical cytoplasm of mature oocytes, contain glycoproteins, are devoid of polyphenols and are similar in structure and composition to the cortical granules observed in some Digenea and Monogenea. Vitellocytes are typical secretory cells with well-developed R.E.R. and Golgi complexes which are involved in the production of shell globules and yolk. The multigranular pattern and the polyphenolic composition of the shell globules of the temnocephalids investigated are similar to those observed in other rhabdocoels, and in some Prolecithophora and Neodermata. This feature may represent a synapomorphy shared by these taxa. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ultrastructural and cytochemical aspects of oogenesis in Castrada viridis (Platyhelminthes, Rhabdocoela).

The heterocellular female gonad of the typhloplanoid Castrada viridis consists of a single germarium and two rows of vitellaria. The germarium, composed of a germinative zone and a growth zone, is surrounded externally by a layer of accessory cells the function of which is hypothesized in this study. The main feature of oocyte differentiation is the synthesis of small electron-dense inclusions produced by the rough endoplasmic reticulum (R.E.R.) and Golgi complex. The electron-dense content of the egg inclusions reacts positively to the cytochemical test used to detect polyphenols and is only partially extracted following incubation in protease. The genesis, composition, and peripheral location of egg inclusions in mature oocytes suggest that they could represent residual eggshell granules. The presumed function of eggshell granules is discussed and their fine morphology is compared with that observed in other neoophoran Platyhelminthes.     

Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida)

Temereva, E.N., Malakhov, V.V. and Yushin, V.V. 2011. Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida). —Acta Zoologica (Stockholm) 92 : 241–250. The successive stages of oogenesis in Phoronopsis harmeri were examined by electron microscopy methods. During the oogenesis, each oocyte is encircled by vasoperitoneal (coelomic) cells forming a follicle. The previtellogenic oocytes are small cells which accumulate ribosomes for future synthesis; their cytoplasm contains characteristic clusters of mitochondria and osmiophilic particles resembling a germ plasm of other metazoans. The cytoplasm of the vitellogenic oocytes includes numerous mitochondria, cisternae of the rough endoplasmic reticulum, Golgi bodies and annulate lamellae. The synthesis of three types of inclusions was observed: strongly osmiophilic granules (lipid droplets) as a prevalent component, distinctly larger granules surrounded by membrane (proteinaceous yolk) and numerous large vesicles with pale flocculent content. No inclusions which could be unequivocally interpreted as the cortical granules were detected. The surface of the vitellogenic oocytes is covered by microvilli which increase in number and length during development. The oogenesis in Phoronida may be interpreted as follicular because of close association of oocytes with the vasoperitoneal tissue. However, well‐developed synthetic apparatus together with a strongly developed microvillous surface and absence of endocytosis indicate a clear case of autosynthetic vitellogenesis. Thus, in phoronids, there is a combination of simply developed follicle and autosynthesis that, apparently, is plesiomorphic character.     

Ultrastructural and cytochemical aspects of the female gonad of Geoplana burmeisteri (Platyhelminthes, Tricladida, Terricola)

The ultrastructure of the female gonad of the land planarian Geoplana burmeisteri was investigated by means of electron microscopy and cytochemical techniques. It consists of two small germaria located ventral to the intestine and of two irregular, lateral rows of vitelline follicles, both enveloped by a tunica composed of an extracellular lamina and an inner sheath of accessory cells. Accessory cell projections completely surround developing oocytes and vitellocytes. The main feature of oocyte maturation is the appearance of chromatoid bodies and the development of the rough endoplasmic reticulum (RER) and Golgi complexes. These organelles appear to be correlated with the production of egg inclusions of medium electron density, about 1.5-1.8 microm in diameter, which remain scattered in the ooplasm of mature oocytes. On the basis of cytochemical tests demonstrating their glycoprotein composition, these inclusions were interpreted as residual yolk globules. Vitellocytes are typical secretory cells with well-developed RER and Golgi complexes that are mainly involved in the production of yolk globules and eggshell globules, respectively. Eggshell globules appear to arise from repeated coalescence of small Golgi-derived vesicles and, at an intermediate stage of maturation, show a multigranular pattern. Later, after vesicle fusion, they reach a diameter of 1.3-1.6 microm when completely mature and show a meandering/concentric pattern, as is typical of the situation seen in most Proseriata and Tricladida. The content of yolk globules is completely digested by pronase, while the content of eggshell globules is unaffected. Mature vitellocytes contain, in addition, a large quantity of glycogen and lipid droplets as further reserve material. On the basis of the ultrastructural characteristics of the female gonad described above and in relation to the current literature, we conclude that G. burmeisteri appears to be more closely related to the freshwater triclads, in particular to members of the Dugesiidae, than to the marine triclads.     

Electron microscopical observations on vitellocytes and germocytes inNematoplana coelogynoporoides (Plathelminthes,Proseriata)

Summary Fine-structural features of vitellaria and germaria inNematoplana coelogynoporoides are documented and compared with those of other free-living plathelminths with ectolecithal eggs. Emphasis is mainly put on the pattern of eggshell material, yolk bodies deposited in vitellocytes, and marginal granules of the female germ cells. In this species, encompassed in the taxon Proseriata Unguiphora, the eggshell granules show a meandering pattern also known from species of the taxon Proseriata Lithophora. In contrast, the yolk globules exhibit crystalline components unknown from the Lithophora. The marginal granules in the ooplasm have an extremely large diameter. They consist of a flocculent core and a crescent-shaped cortex. Marginal granules of this appearance have not been found in any other taxon of free-living Neoophora.Abbreviations cc crystalline component - co cortex - gER granular endoplasmic reticulum - go Golgi complex - gl glycogen - lp lipid droplet - mg marginal granule - n nucleus - nl nucleolus - sg eggshell granule - sp spermatozoa - yg yolk globule     

Muco-follicle cells of the jelly coat in the oocyte envelope of the sheatfish (Silurus glanis L.)

During early vitellogenesis of the oocytes of Silurus glanis, the follicular cells proliferate, their epithelial organization becomes disrupted, and they transform into an irregularly structured large mass of cells engaged in intensive secretory activity. They contain nuclei, rough endoplasmic reticulum, Golgi bodies, and secretory inclusions termed “acorn bodies,” which are synthesized in the cytoplasm. The acorn bodies have two components: an electron-dense cap and a moderately electron-dense body. As development proceeds, the acorn bodies become modified into spherules of mucous material, the mucosomes. The electron-dense part persists as a small calotte or crescent often irregularly structured at the periphery of the mucosome, and fragments of it are dispersed into the interior of the mucosomal body. The mucosomes are membrane-bound and contain small granules, 55 nm in diameter. At the end of vitellogenesis, the follicle cells are filled with mucosomes, and cytoplasmic residua can only sparingly be observed among them. Oocytic microvilli extend through the zona radiata and intermingle with follicular cell processes in the cleft between the zona radiata and the belt of mucosomes during growth of the oocyte. Capillaries develop in connective tissue of the theca layer as vitellogenesis proceeds. © 1993 Wiley-Liss, Inc.     

Ultrastructural and cytochemical studies on the germarium of Dicrocoelium dendriticum (Plathelminthes,Digenea)

Summary The unpaired germarium of Dicrocoelium dendriticum contains many female germ cells at different stages of maturation and is enveloped by a fibrous basal lamina-like structure and a multilayered cytoplasmic sheath whose origins and functions are discussed. The maturation process of primary oocytes occurs completely within the prophase of the first meiotic division. It has been divided into three stages, as previously suggested for monogeneans. Stage I corresponds to oogonia and early oocytes which are located in the distal germinative area of the gonad. These cells are characterized by a high nucleo/cytoplasmic ratio and a poorly differentiated cytoplasm. Stage II corresponds to maturing oocytes grouped in the central area of the gonad and exhibiting long synaptonemal complexes and a prominent nucleolus. The main feature of cytoplasmic differentiation is the increase in the number of RER and Golgi complex which are involved in the production of small electron-dense granules. Stage III corresponds to mature oocytes located in the proximal area of the germarium near the origin of the oviduct. In this stage, the granules become regularly distributed in a monolayer in the peripheral ooplasm and make contact with the oolemma. They show a distinctive complex structure, are composed of proteins and glycoproteins and do not contain polyphenols. Their possible role as cortical granules is discussed in relation to chemical composition and previous studies on other Plathelminthes. Neither yolk globules nor glycogen are present in the oocytes.Abbreviations I oogonium and early oocyte - II growing oocyte - III mature oocyte - cg cortical granule - cs cytoplasmic sheath - db dense body - ecm extra cellular matrix - ER endoplasmic reticulum - fl fibrous extracellular layer - gc Golgi complex - m mitochondria - N nucleus - nu nucleolus - RER rough endoplasmic reticulum - sc synaptonemal complex     

Previtellogenic oocytes of South African largemouth bass Micropterus salmoides Lacépède 1802 (Actinopterygii,Perciformes) - the Balbiani body,cortical alveoli and developing eggshell

The ovaries of the largemouth bass Micropterus salmoides, an alien and invasive species in South Africa, contain a germinal epithelium which consists of germline and somatic cells, as well as previtellogenic and late vitellogenic ovarian follicles. The ovarian follicle consists of an oocyte surrounded by follicular cells and a basal lamina; thecal cells adjacent to this lamina are covered by an extracellular matrix. In this article, we describe the Balbiani body and the polarization and ultrastructure of the cytoplasm (ooplasm) in previtellogenic oocytes. The nucleoplasm in all examined oocytes contains lampbrush chromosomes, nuclear bodies and several nucleoli near the nuclear envelope. The ultrastructure of the nucleoli is described. Numerous nuage aggregations are present in the perinuclear cytoplasm in germline cells as well as in the ooplasm. Possible roles of these aggregations are discussed. The ooplasm contains the Balbiani body, which defines the future vegetal region in early previtellogenic oocytes. It is comprised of nuage aggregations, rough endoplasmic reticulum, Golgi apparatus, mitochondria, complexes of mitochondria with nuage-like material, and lysosome-like organelles. In mid-previtellogenic oocytes, the Balbiani body surrounds the nucleus and later disperses in the ooplasm. The lysosome-like organelles fuse and transform into vesicles containing material which is highly electron dense. As a result of the fusion of the vesicles of Golgi and rough endoplasmic reticulum, the cortical alveoli arise and distribute uniformly throughout the ooplasm of late previtellogenic oocytes. During this stage, the deposition of the eggshell (zona radiata) begins. The eggshell is penetrated by canals containing microvilli and consists of the following: the internal and the external egg envelope. In the external envelope three sublayers can be distinguished.     

The evolution of the female gonad in Platyhelminthes-Turbellaria: ultrastructural investigations

Summary

The structure of the female gonad has undergone important evolutionary modifications in Platyhelminthes-Turbellaria. The primitive condition consists of single oocytes freely distributed in the parenchyma autosynthetically producing both yolk and eggshell forming granules (e.f.g.) (archoophoran level of organization). A derived condition is the presence of a compact, hetero-cellular gonad enveloped by a cellular tunica and/or an extracellular lamina-like layer and composed of germaria with alecithal oocytes and vitellaria with vitelline or yolk cells producing and accumulating both yolk and e.f.g. (neoophoran level of organization). In the last three decades the female gonad of a number of turbellarian taxa has been investigated by means of electron microscopy and cytochemistry, and several characters of oocytes and vitellocytes have been hypothesized to have a potential phylogenetic value. Some of these characters and their possible phylogenetic implications are briefly reviewed.     

Ultrastructural features of oogenesis in a free-living marine Platyhelminth, Vorticeros luteum

The female gonad of the prolecithophoran turbellarian Voticeros luteum has a heterocellular organization as is typical in the neoophoran Platyhelminthes. It is composed of an ovarian and a vitellarian area that are not well separated from one another and from the surrounding tissues by a tunica. Each oocyte during maturation becomes completely surrounded by a single accessory cell whose function has been hypothesized on the basis of the present investigation. The main feature in oocyte differentiation appears to be the synthesis and accumulation of small electron-dense inclusions; these are about 1-2 mum in size, are elaborated by the Golgi apparatus and have a content which reacts partially to the cytochemical test for polyphenols. The genesis, composition and cortical localization of the inclusions suggest that they could be homologous to the egg-shell granules present in the oocytes of 'archoophoran' species. A comparative analysis and discussion of the oocyte inclusions observed to date in other turbellarians is undertaken and the hypothetical use of these structures as characters providing some new insights in clarifying the phylogenetic relationships among free-living Platyhelminthes is finally discussed.     

Oogenesis in Actinoposthia beklemischevi (Platyhelminthes, Acoela): an ultrastructural and cytochemical study

The oogenesis of the acoel Actinoposthia beklemischevi can be divided into a previtellogenic and a vitellogenic stage. Maturing oocytes are surrounded by accessory cells (a.c.) that produce electrondense granules, the content of which is released into the space between the oocyte and a.c. and gives rise to a thin primary egg envelope. The a.c. may also contribute to yolk synthesis by transferring low molecular weight precursors to the oocyte. Two types of inclusion are produced in maturing oocytes. Type I inclusions are small, roundish granules produced by the Golgi complex. They have a proteinaceous non-polyphenolic content which is discharged in the intercellular space and produce a thicker secondary egg envelope. Type I inclusions represent eggshell-forming granules (EFGs). Type II inclusions are variably sized globules progressively changing their shape from round to crescent. They appear to be produced by the ER, contain glycoproteins and remain scattered throughout the cytoplasm in large oocytes. Type II inclusions represent yolk. The main features of oogenesis in Actinoposthia are: (a) EFGs have a non-polyphenolic composition; (b) the egg envelope has a double origin and is not sclerotinized; (c) yolk production appears to be autosynthetic. The present ultrastructural findings are compared with those from other Acoelomorpha and Turbellaria.     

Fine Structures of Oocytes and Accessory Cells of the Ovary in the Starfish Patiria (Asterina) pectinifera at Different Stages of Oogenesis and After 1-Methyladenine-Induced Maturation

Morphological changes in the growing and maturing oocytes of Patiria ( Asterina ) pectinifero were studied by electron microscopy. Oogenesis is of the solitary type. An extensive system of rough endoplasmic reticulum (ER) and Golgi complex (GC) develops in the ooplasm forming the cortical, yolk and secretory granules in its peripheral regions. The contents of the latter granules are released from the oocyte and form the vitelline membrane. At early stages of oogenesis, extensive multiplication of mitochondria results in formation of a large aggregate of these organelles in the perinuclear cytoplasm ("yolk nucleus"). After maturation of full grown oocytes has been induced by 1-methyladenine, the membranous cell structures are rapidly rearranged: vast aggregates of ER cisternae in the surface cytoplasm layer and single ER cisternae among yolk granules are disintegrated to small vesicles; the GC is reduced. These processes are suggested to be somehow related to changes in hydration of the cytoplasm and in rigidity of its surface layer. In maturing oocytes, the yolk granules form characteristic linear rows, trabeculae, traversing the cytoplasm and their boundary membranes fuse in zones of contact. Some granules are converted to multivesicular bodies, thus suggesting the activation of hydrolytic enzymes that form part of the yolk in echinoderms.     

Ultrastructural studies on vitellocytes of Parotoplaninae (Plathelminthes,Proseriata) with special reference to the structure of eggshell-forming granules

Summary The general organisation of the vitellocytes inParotoplana capitata, P. papii, Parotoplanella progermaria, andP. heterorhabditica is described. Special emphasis is put on the substructure of eggshell-forming granules. In all parotoplanid species studied the eggshell granules show uniformly shaped substructures typical of all the Proseriata and besides this feature, globules exist which are bipartite, i.e. two different patterns exist within the same granule. This characteristic, which is unknown for other taxa of the Proseriata, is hypothesized as an autapomorphy of the monophylum Parotoplaninae.Abbreviations gER granular endoplasmic reticulum - lp lipid droplets - n nucleus - sg eggshell granule - y yolk platelet     

Fine structure and formation of eggshells in marine Gastrotricha

Summary The fine structure of the gastrotrich eggshell in the hermaphroditic species Turbanella ocellata (Hummon 1974) and the parthenogenetic species Aspidiophorus sp. is described using transmission electron microscopy. The presented evidence strongly suggests that the shell is produced by the egg itself prior to oviposition in both species. The layed egg in Aspidiophorus sp. is provided with a special attachment stalk that is also preformed in the mother animal. Freshly layed eggs of T. ocellata are adhesive all around their surface and lack any specialized structures for attachment. Formation of the spiny eggshell of Aspidiophorus sp. appears to begin with a sudden release of special vesicles containing the preformed spines of the outer eggshell covering. Additional material appears to be secreted by the egg in a more gradual process after the initial vesicle release. The formation of the two fibrous layers in the eggshell of T. ocellata is less well understood and deposition of eggshell material could be seen either as a continuous process or as two separate steps, similar to the events observed for Aspidiophorus sp. For T. ocellata, Tetranchyroderma sp. and Aspidiophorus sp. it is demonstrated that formation of the cuticle occurs as an independent process from that of eggshell formation. This is significantly different from the basic mode of cuticle formation in the annelid line of evolution. The paper argues further that the data support earlier claims of a pronounced difference between the Gastrotricha-Macrodasyida and the Gastrotricha-Paucitubulatina and agree well with the postulated ties of the Gastrotricha and Nematoda. The phylogenetic importance of the eggshell fine-structure is discussed in the framework of present theories on aschelminth phylogeny.Abbreviations cus cuticular spines - cut cuticle - cov coated vesicles - cv cup-shaped vesicles - dp dense particles - ep epidermis - emb embryo - erl lacunae of smooth ER - fgb fibrous and granular bodies - fl fibrous layer - ga Golgi apparatus - gc gut cell - gv Golgi vesicles - im intercellular matrix - isp intercellular space - isl inner shell layer - ld lipid droplet - mdb medium-dense bodies - mvb multivesicular bodies - oc oocyte - od oviduct - osl outer shell layer - o egg - sv spiny vesicles - sh eggshell - st egg-stalk - sl spiny layer - sub substrate - trm trilaminate membrane - yb yolk bodies - yg yolk granule - yoc young oocyte This work was supported by NSF Grant # GB-42211 to R.M. Rieger     

Oogenesis in the terrestrial hermit crab Coenobita clypeatus (decapoda,anomura). I. Previtellogenic oocytes

Ultrastructural study of previtellogenic oocytes found in cystlike clusters scattered throughout the length of the bilobed ovary of the hermit crab Coenobita clypeatus shows a high nuclear:cytoplasm ratio. Large, round nuclei containing synaptinemal complexes serve as good temporal markers for identification of previtellogenic oocytes. The cytoplasm contains many smooth-membraned vesicles filled with granules and probably of nuclear origin. In addition to its complement of Golgi complexes, endoplasmic reticulum, mitochondria, and free ribosomes, the cytoplasm also contains stacks of annulate lamellae, a feature not previously described for decapod oocytes. Typically, the previtellogenic oocyte with its accumulation of ribosomes has the appearance of a nonsynthetic cell preparing to go through a metabolic transition.     

Electron microscopic study on the thyroid gland of the salamander Hynobius nebulosus in the breeding season

Summary The thyroid gland of adult salamanders, Hynobius nebulosus, in the breeding season was studied by electron microscopy. The follicular cells are different in cell height and fine structures; the taller cells with many cell organelles and granules and the lower cells with a few cell organelles and granules are both present in the same follicle. In the cytoplasm, three types of membrane-bounded granules, namely, cytosomes, colloid droplets, and vacuolar bodies and circular membrane complexes occur. The vacuolar bodies are subdivided into two types; the ordinary type having loosely distributed particles and the specific type containing tubules and/or closely packed filaments, crystalloid structures, except for the particles. The chromophobe colloids within the Bensley-cells correspond to extremely large, ordinary type vacuolar bodies, while the Langendorff-colloid cells possess increased numbers of granular cisternae of endoplasmic reticulum and a ribosome-rich, dense cytoplasmic matrix but not extremely large colloid. The intracytoplasmic circular membrane complexes appear in the Golgi area of cytosome-rich cells. It is suggested that they originate from the Golgi apparatus which was activated to produce many cytosomes. Intranuclear inclusions consisting of microtubules and filaments and tight junctions between two adjacent lateral plasma membranes are occasionally encountered.