Observations on the fine structure,enzyme histochemistry,and innervation of parathyroid gland and ultimobranchial body of Chthonerpeton indistinctum (Gymnophiona,Amphibia)

Summary Fine structural and enzyme histochemical observations on ultimobranchial body and parathyroid gland of the caecilian Chthonerpeton are presented. The cell clusters and follicles of the ultimobranchial body consist mainly of granulated cells which are termed C-cells and obviously belong to the APUD cell series. In the larger follicles additional possibly exhausted degranulated cells and replacement cells occur. A rich supply of nerve fibres has been found in this gland. Frequently nerve terminals were observed to come into synaptic contact with the C-cells. Two categories of nerve fibres occur: a) fibres containing large polymorphic electron dense granules (probably purinergic fibres), b) fibres containing small electron transparent vesicles and a few electron dense granules (probably cholinergic fibres). The parathyroid gland consists of elongated cells (one cell type) poor in organelles and often containing fields of glycogen and lipid droplets. The cells are further characterized by fair amounts of lysosomal enzymes; they are interconnected by maculae adhaerentes and occludentes. No nerves and blood vessels have been found in the parathyroid gland of Chthonerpeton. This study has been supported by the Deutsche Forschungsgemeinschaft We 380/5.     

The Pituitary Gland of the Roach Leuciscus rutilus

Three endocrine cell types were recognized in the proximal pars distalis (PPD) of the roach, Leuciscus rutilus, by electron microscopy. Two of these cell types are basophilic and assumed to be gonadotropic. The third cell type is acidophilic and its similarity to somatotropic (STH) cells is evident. Green fluorescent cells corresponding to cells with dense core vesicles of about 85 nm are scattered between the PPD and the proximal neurohypophysis (PNH). Their possible content of a catecholamine was demonstrated with microspectrofluorometric analyses. Four axon types with granules 65, 81, 110 and 137 nm in average diameter terminate at the basement membrane. Only fibers with granules of 81 nm enter the PPD to make synapses with the STH cells. Extensions of the basement membrane are continuous with the perivascular space and penetrate the endocrine tissue. It is postulated that axon terminals on the basement membrane are functionally equivalent to synaptic contacts on the endocrine cells. Axon type 4 has granules which in sizes correspond to those of cells in lateral and ventrolateral parts of the nucleus lateralis tuberis (NLT). A similar correlation is possible between axon type 3 and other cells in the NLT. This is in accordance with earlier conclusions of a regulation of the gonadotropic cells from the lateral (posterior) parts of the NLT.     

An electron microscopic study of the salivary gland of Rhynchosciara angelae

Summary The structure of the salivary gland of the dipteran insect Rhynchosciara angelae in a defined stage of the larval development, characterized by the synthesis and storage of secretion product, is described. Observations were made with both Nomarski optics and electron microscopy. Filiform projections extending into the lumen of the gland were observed in the apical portion of the cells. At the basal region junctions, characterized as hemidesmosomes, were observed between the membrane of the cell and the basal lamina. The plasma membrane presents numerous infoldings into the cell increasing considerably the surface area at this region. Throughout the cytoplasm of the gland cells numerous mitochondria, Golgi complexes, microtubules, profiles of endoplasmic reticulum, secretion granules and glycogen granules were observed. Carbohydrates were detected on ultrathin sections by using the periodic acid-silver methenamine and the periodic acid-thiosemicarbazide-silver proteinate techniques.     

Occurrence of innervation in labral glands of Daphnia obtusa (crustacea,cladocera)

Electron microscopy discloses nerve endings in contact with gland cells situated in the labrum of Daphnia. Swellings of nerve fibers are in close contact with gland cell membranes, either on the cell surface or inserted into infoldings of plasma membrane. The axonal processes are single or double and lack glial wrappings. Inside the nerve fibers are vesicles of different sizes and electron density. These include granular vesicles, which often are dense-cored, and also clearer vesicles. Some presynaptic differentiations lie along the contact line of the axonal process with the gland cell membrane. The significance of the vesicles is discussed in terms of their possible content of biogenic amines, as described in other invertebrates.     

Ultrastructural study of the bacillary, granular and mucoid proboscidial gland cells of Riseriellus occultus (Nemertini, Heteronemertini)

Junoy, J., Montalvo, S., Roldán, C. and García‐Corrales, P. 2000. Ultrastructural study of the bacillary, granular and mucoid proboscidial gland cells of Riseriellus occultus (Nemertini, Heteronemertini). — Acta Zoologica (Stockholm) 81 : 235–242. The ultrastructure of six types (G₅‐G₁₀) of proboscidial gland cells whose cell necks emerge independently on the epithelium surface is analysed and compared with data from other nemerteans. These types differ in cytological features, as well as in the morphology of their respective secretory granules. Secretory granules of the types G₅ and G₆ have a bacillary shape, and differ from each other based on their contents and dimensions. Secretory granules of the types G₇ and G₈ are spherical to ovoid; type G₈ gland cells are monociliated, and their secretory granules contain a paracrystalline material. Types G₉ and G₁₀ gland cells are typically goblet‐shaped; secretory granules in the type G₉ have a spherical shape, contain a homogeneous electron dense material and maintain their individuality, whereas those of the G₁₀ type are elongate and have fibrillar contents, showing a tendency to fuse before they are extruded. The mucus sheet of the proboscis is responsible for lubrication of its epithelial surface. Secretion products of type G₁₀ gland cells form the background substance of this mucus, and those of the G₅ type confer stickiness to it. Type G₉ gland cells could provide the toxic component to the mucus, and type G₇ and G₈ gland cells could be concerned with the production of enzymatic secretions.     

Fine structure of the posterior salivary gland ofEledone cirrosa andOctopus vulgaris

Summary The posterior salivary gland of Octopods comprises a parenchyma of branching tubules in a connective tissue stroma. The tubules are lined by either of two distinct epithelia.Type A is composed predominantly of columnar cells containing large granules whose contents vary in appearance from cell to cell.Type B consists of three cell types: A circumferential layer of processes ofstriated cells containing radially orientated infoldings of the cellular membrane, between which are packed numerous mitochondria;cistern cells which contain an invaginated system of membrane loops, the interior of which is in communication with the lumen; andlumen lining cells. All these cells send processes to the basement membrane of the tubule, so that both epithelia are pseudostratified. The functional significance of this cytological specialisation is discussed.Thanks are due to Prof. J. Z. Young F. R. S. and Prof. E. G. Gray for helpful discussion and use of facilities during the course of this study, and to Prof. Young for the loan of the Cajal preparations. I also wish to thank Miss E. Franke for excellent technical assistance.     

Activity of the ovarian germinal epithelium in the freshwater catfish,Pimelodus maculatus (Teleostei: Ostariophysi: Siluriformes): Germline cysts,follicle formation and oocyte development

Distinct types of oogonia are found in the germinal epithelium that borders the ovarian lamellae of Pimelodus maculatus: A‐undifferentiated, A‐differentiated and B‐oogonia. This is similar to the situation observed for spermatogonia in the vertebrate testis. The single A‐undifferentiated oogonia divide by mitosis giving rise to A‐groups of single differentiated oogonia, each enclosed by epithelial cells that are prefollicle cells. Subsequently, the single A‐differentiated oogonia proliferate to generate B‐oogonia that are interconnected by cytoplasmic bridges, hence, forming germline cysts. The prefollicle cells associated with them also divide. Within the germline cysts, B‐oogonia enter meiosis becoming oocytes. Meiotic prophase and early folliculogenesis occur within the germline cysts. During folliculogenesis, prefollicle cells grow between the oocytes, encompassing and individualizing each of them. The intercellular bridges disappear, and the germline cysts are broken down. Next, a basement membrane begins to form around the nascent follicle, separating an oocyte and its associated prefollicle cells from the cell nest. Folliculogenesis is completed when the oocyte and the now follicle cells are totally encompassed by a basement membrane. Cells derived from the ovarian stroma encompass the newly‐formed ovarian follicle, and become the theca, thereby completing the formation of the follicle complex. Follicle complexes remain attached to the germinal epithelium as they share a portion of basement membrane. This attachment site is where the oocyte is released during ovulation. The postovulatory follicle complex is continuous with the germinal epithelium as both are supported by a continuous basement membrane. The findings in P. maculatus reinforce the hypothesis that ovarian follicle formation represents a conserved process throughout vertebrate evolution. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Ultrastructure of the neurohypophysis of the teleost Poecilia latipinna in relation to neural control of the adenohypophysial cells

Summary The structure of the neurohypophysis of Poecilia latipinna (green molly, sailfin molly) was studied with the electron microscope. Profile diameters of neurosecretory granules in the non-myelinated neurohypophysial nerve fibres were measured and mathematically corrected for error due to section thickness. Six different types of nerve fibres could be distinguished by statistical classification of their granules and by other ultrastructural features. One fibre-type (type B) contained granules with a mean diameter of 85 nm, and the other five types (types Ala, Alb, A2, A3 and A4) all contained granules with mean diameters greater than 100 nm. Synaptic contacts were observed between type B fibres and all the adenohypophysial cell-types, although in the case of the ACTH cells the synapses were separated from the cell membrane by a continuous double basement membrane. Type A fibres were observed to contact the cells of the proximal pars distalis and pars intermedia, but did not form synapses. However, synapses occurred between type A fibres and pituicytes, and between type A fibres and the pericapillary basement membrane in the interior of the neurohypophysis. The possible roles of the different types of nerve fibres in controlling the adenohypophysial cells are discussed in the context of evidence from other teleosts.We thank Mr. W.A. Thomson and Mr. D.I. Hollingworth for technical assistance, and Dr. D.I.C. Pearson (Department of Physics, University of Nancy, Nancy, France) for advice on mathematical analysis and computer programs. The work was carried out during the tenure of an S.R.C. Research Studentship by T.F.C.B.     

Human keratinocytes cultured on collagen gels form an epidermis which synthesizes bullous pemphigoid antigens and α2β1 integrins and secretes laminin, type IV collagen, and heparan sulfate proteoglycan at the basal cell surface

Single cell suspensions of human keratinocytes when seeded onto floating three-dimensional gels constructed with type I collagen form a tissue resembling epidermis. These morphogenetic events occur in a serum-free environment in the absence of fibroblasts. Light and transmission electron microscopy show that cells form a basal layer plus suprabasilar cell layers corresponding to the stratum spinosum, stratum granulosum, and stratum corneum. The suprabasilar keratinocyte layers show morphologies which resemble intact skin in which cells are connected by desmosomes and contain intermediate filaments and keratohyalin-fillagrin granules. The basal cell layer differs from skin in vivo in that there is no connection to a basement membrane via hemidesmosomes. Cells in the basal layers are polarized as evidenced by the secretion of type IV collagen, heparan sulfate proteoglycans, and laminin at the cell membrane interface with the collagen gel. These proteins are not organized into a cytological basement membrane. Bullous pemphigoid antigen, a protein component of hemidesmosomes, is synthesized by basal keratinocytes, but like the basement membrane proteins it is not incorporated into a definable cytological structure. Keratinocytes in the basal and suprabasilar layers also synthesize α2β1 integrins. The mechanisms of keratinocyte adhesion to the gel may be through the interactions of this cell surface receptor with laminin and type IV collagen synthesized by the cell and/or direct interactions between the receptor and type I collagen within the gel. This in vitro experimental system is a useful model for defining the molecular events which control the formation and turnover of basement membranes and the mechanisms by which keratinocytes adhere to type I collagen when sheets of keratinocytes are used clinically for wound coverage.     

Ultrastructure of the tubular nephron of the lizard Podarcis (= Lacerta) Taurica

The proximal, intermediate, and distal convoluted tubules of the neprhon of Podarcis (= Lacerta) taurica were examined by electron microscopy. Proximal tubule cells have large, apical cytoplasmic protrusions and microvilli interpreted to function in urate secretion. Adjacent cells are bound apically by tight junctions and desmosomes but interdigitate in their basal region. This situation is repeated in the other tubules with significant differences in intercellular space width. The basal surfaces bear numerous cytoplasmic processes. The intermediate tubule has proximal and distal segments each with dark, ciliated, and light cells, the cuboidal dark cells with dense cytoplasm constituting the main bulk of the wall. As the cells of the proximal and distal segments resemble those of the proximal and distal convoluted tubules, respectively, the intermediate tubule is considered as a transition region. The ciliated cell body has two broad processes extending from the lumen, one to the basement membrane and one to a foot process of a light cell. The light cell is surrounded by dark and ciliated cells. It does not reach the lumen, but contacts the basement membrane through a process running below a ciliated cell to form a mushroom-shaped structure in tubule cross-section, the light cell process forming the stalk and a ciliated cell the cap. The cilia probably propel the glomerular filtrate towards the distal convoluted tubule. This latter tubule has initial, middle, and terminal zones, all nonciliated but with different lumen widths and cell shapes.     

Phylogenetic relationships of the Temnocephaloidea (Platyhelminthes)

Temnocephala novaezealandiae (family Temnocephalidae) and Troglocaridicola mrazeki and Scutariella georgica (family Scutariellidae) were studied by electron microscopy in an attempt to reveal characters that would indicate their phylogenetic relationship to other members of the Platyhelminthes. Ultrastructural features of the epidermis in these temnocephaloideans are like those of the neoophoran turbellarians. The epidermis is syncytial, is honeycombed by a multitude of gland necks whose secretions produce an epidermal surface film, and is underlaid by a thick basement membrane. Some cells in the parenchyma are compartmentalized by intrusive cell processes from neighboring parenchymal cells in a fashion similar to parenchymal structure in the Monogenea and Digenea. The spermatozoa have a pair of free 9+1 flagella and contain aligned dense bodies. The Temnocephaloidea is evidently derived from an early rhabdocoel-turbellarian-like ancestor.     

Ultrastructure of the tubular accessory gland in Haemaphysalis longicornis (Acari: Ixodidae)

The paired tubular accessory glands in Haemaphysalis longicornis open at the junction of the cervical and the vestibular parts of vagina via short and narrow ducts. The pseudostratified columnar glandular epithelium covered by the muscle layer consists of both secretory and supporting cells. As feeding proceeds, the secretory cells increase in volume. In ovipositing females, well-developed rough endoplasmic reticulum, the Golgi complex, and membranebound granules that are undergoing exocytosis suggest that the secretory cells are involved in protein synthesis. However, in virgin females that fed 10 days, only small dense granules and no secretion activity were observed. The secretions from the tubular accessory gland may be released into the genital tract during the egg passage through the vagina. However, the supporting cells located between the secretory cells become slender during feeding, cohere to each other at the luminal side, and have a very narrow attachment at the basement membrane. Supporting cells probably help maintain secretory cell shape especially during granular discharge into the lumen. © 1994 Wiley-Liss, Inc.     

The structure of the nerve fibre layer and neurocord in the enteropneusts

Summary The nerve fibre layer and the neurocord of the Enteropneusts Saccoglossus horsti, Harrimania kupfferi and Ptychodera flava have been examined with the electron microscope. The nerve fibres vary in diameter between 0.15 to 10 m. The majority of the fibres are of the smaller diameters. The nerve fibre layer is intraepidermal, and is divided by processes running radially from the epithelial cells to the basement membrane that separates the nerve fibre layer from the muscle cells.The cells of origin of these nerve fibres are situated mainly in the innermost layers of the epidermal cells. The nerve fibre profiles contain numerous vesicles of very varied diameter and contents, together with larger granular inclusions that are also found in the nerve cell bodies.Morphologically recognisable synapses are rare, but the majority of fibres are in intimate contact with one another. Sometimes the mass of fibres is divided into bundles by the epithelial cell processes. The majority of giant fibres are situated near to the basement membrane of the neurocord. The giant fibres also have a varied content of vesicles as well as neurofilaments and neurotubules.The central canal in Ptychodera flava and the remnants of the central canal in Saccoglossus horsti are both lined by columnar cells that bear microvilli as well as cilia with the typical 9 + 2 pattern of tubules. Scattered amongst these cells are mucus secreting cells which open into the cavity of the canal.I (P.N.D.) should like to thank Professor J. Z. Young, F. B. S. for much advice and encouragement. Dr. R. Bellairs generously provided the electron microscope facilities, and Dr. R. Newell kindly collected and identified the Saccoglossus specimens. Mr. R. Moss, Mrs. J. Hamilton and Mr. A. Aldrich gave excellent technical and photographic assistance.     

Lectin histochemical studies of mouse granulated metrial gland cells

A lectin histochemical study has been carried out on mouse granulated metrial gland cells, the major leucocyte population that differentiates in the uterine wall in pregnancy. The binding characteristics of 26 lectins were examined using light microscopical methods. Fourteen of the lectins, with affinities ranging through N-acetylgalactosamine, galactose, N-acetylglucosamine, mannose and sialic acid residues, bound to the cytoplasmic granules of granulated metrial gland cells, and each appeared to bind to the limiting membrane of the granules. The binding characteristics of three of these lectins (Wheat germ agglutinin, Concanavalin A and Helix pomatia agglutinin) were examined using electron microscopical methods. These showed a different binding pattern to the cytoplasmic granules of granulated metrial gland cells compared with that found using light microscopical methods, as they appeared to bind evenly across the granule's matrix. This binding pattern corresponds to the reactivity of the granule matrix in the periodic acid--Schiff technique. Six lectins bound to the cell membranes of granulated metrial gland cells. These included the E and L isoforms of Phaseolus vulgaris agglutinin, with affinities for complex carbohydrates, whose binding differences were related to the stage of differentiation of the granulated metrial gland cells. The lectin binding described presents additional markers of granulated metrial gland cells and tools for investigating carbohydrate moieties in the functional activities of granulated metrial gland cells This revised version was published online in November 2006 with corrections to the Cover Date.     

Ultrastructural, histochemical and cytochemical characterization of intestinal epithelial cells in Aplysia depilans (Gastropoda, Opisthobranchia)

To improve the current knowledge about the digestive system in opisthobranchs, light and electron microscopy methods were used to characterize the epithelial cells in the mid‐intestine of Aplysia depilans. This epithelium is mainly formed by columnar cells intermingled with two types of secretory cells, named mucous cells and granular cells. Columnar cells bear microvilli on their apical surface and most of them are ciliated. Mitochondria, multivesicular bodies, lysosomes and lipid droplets are the main components of the cytoplasm in the region above the nucleus of these cells. Peroxisomes are mainly found in middle and basal regions, usually close to mitochondria. Mucous cells are filled with large secretory vesicles containing thin electron‐dense filaments surrounded by electron‐lucent material in which acidic mucopolysaccharides were detected. The basal region includes the nucleus, several Golgi stacks and many dilated rough endoplasmic reticulum cisternae containing tubular structures. The granular cells are characterized by very high amounts of flat rough endoplasmic reticulum cisternae and electron‐dense spherical secretory granules containing glycoproteins. Enteroendocrine cells containing small electron‐dense granules are occasionally present in the basal region of the epithelium. Intraepithelial nerve fibres are abundant and seem to establish contacts with secretory and enteroendocrine cells.     

云南树鼩肝脏结构的光,电镜观察

本文报告了树肺脏的一般结构和超微结构。与人和灵长目相似，其肺实质也是由导气部和呼吸部构成。但不同的是其细支气管粘膜形成很高的皱襞。在电镜下Ｃｌａｒａ细胞电子密度高，顶部胞质中含有大量膜包颗粒，这些结构与大白鼠和家兔的结构相似。许多毛细血管外方都包绕着基膜和肺泡Ⅰ型上皮细胞的胞质。气血屏障由肺泡上皮细胞、融合的基膜和内皮细胞胞质构成。说明树肺脏不但是呼吸器官，也是一些激素和介质产生及代谢的重要器官。本文为研究树的正常生理功能及分类提供形态学资料。     

The blood-testis barrier in Aphanius dispar (Teleostei)

Summary Thin sections of normal testes from the cyprinodont Aphanius dispar were studied by electron microscopy after intravascular injection of live specimens with horseradish peroxidase. The intercellular space in the spermatogenic cysts is marked differently by the tracer according to the degree of differentiation of the germ cells. Spermatogonia and gonocytes undergoing meiosis are surrounded by a dark band of the marker. This band gradually disappears during spermiogenesis. In cysts containing ripe spermatozoa, the marker penetrates a short distance between the bases of adjoining Sertoli cells bordering the cysts, but is arrested by tight junctional complexes near the lumina of the cysts. The tight junctions between the Sertoli cells provide a permeability barrier between the vascular spaces of the stroma and the lumina of ripe cysts.Abbreviations BM basement membrane - BTB blood-testis barrier - HRP horseradish peroxidase This research was supported by a grant from the National Council for Research and Development, Israel, and the GKSS Geesthacht-Tesperhude, Federal Republic of Germany     

The Pituitary Gland of the Roach Leuciscus rutilus

Abstract Two endocrine cell types, PbH+ and PAS+ cells, were recognized in the pars intermedia (PI) of the roach, Leuciscus rutilus, by light and electron microscopy. They can be distinguished by the appearance of their secretory granules. The PAS+ cells stain with toluidine blue in semithin sections as opposed to the PbH+ cells. After 5 days' treatment with metopirone the PbH+ cells are highly activated whereas the PAS+ cells show no response. The PbH+ cells are assumed to produce MSH. In roaches adapted to diluted sea water (10%) the transfer to fresh water for 1—1 1/2 hours or reserpine injections for the same period had no notable effect on neither cell type. Three kinds of axons innervate the PI. Two of these, which have granules averaging 111 nm and 151 nm in diameter, originate in the nucleus preopticus (NPO). The third type of axons has granules of an average size of 74 nm and is probably aminergic. The glia cells in this part of the neurohypophysis (NH) are granular pituicytes, which are innervated by all three axon types. The border between the NH and the PI is composed of a double basement membrane from which a network extends into the NH. This network, the basement membrane and the capillaries are the main sites for the terminations of the axons although nerve fibers also invade the endocrine tissue. Only axon type 3 was observed to synapse frequently with the PbH+ cells.     

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.     

Ultrastructure of male accessory glands of Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae)

The ultrastructure of the male accessory glands of the blow fly, Chrysomya megacephala (Fabricius), was presented using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A pair of accessory glands was separated at opposite sites. Morphometric results using LM yield evidenced no significant difference in the median of either length or width of the left and right glands. A significant increment in both length and width was seen to plateau between three to six days. SEM observation showed that the surface of the glands revealed a faint irregular groove pattern throughout, and it was occasionally penetrated by tracheoles. Each gland was a slender, elongated sac‐like tubule having apical rounded ends, with a slight constriction at the sub‐apical part of the gland being observed occasionally. TEM analyses of three‐day‐old males showed that the glands consisted of external capsular cells with a basement membrane underneath, glandular cells, and gland lumen. The capsular cell was flat and contained a nucleus with electron dense material in the nuclear envelope. The glandular cell, appearing as columnar, consisted of a vacuolated component that contained a large oval nucleus centrally or sub‐basally located, with dense mitochondria, numerous rough endoplasmic reticulum, and secretory vesicles containing electron‐lucent materials. In the gland lumen, the cross‐section through the middle portion revealed dense secretory materials, characterized by electron‐dense materials. Some sections revealed a large lumen where secretion accumulates within the delicate sac. The seven‐day‐old glands exhibited a remarkable change in the lumen, where the whole space contained a large amount of secretory materials, with the electron‐dense materials being characterized as similar to those observed in three‐day‐old glands. About four prominent types of secretions were observed on the basis of difference in electron‐density.