ACTIVE TRANSPORT BY THE CECROPIA MIDGUT : II. Fine Structure of the Midgut Epithelium

A morphological basis for transcellular potassium transport in the midgut of the mature fifth instar larvae of Hyalophora cecropia has been established through studies with the light and electron microscopes. The single-layered epithelium consists of two distinct cell types, the columnar cell and the goblet cell. No regenerative cells are present. Both columnar and goblet cells rest on a well developed basement lamina. The basal portion of the columnar cell is incompletely divided into compartments by deep infoldings of the plasma membrane, whereas the apical end consists of numerous cytoplasmic projections, each of which is covered with a fine fuzzy or filamentous material. The cytoplasm of this cell contains large amounts of rough endoplasmic reticulum, microtubules, and mitochondria. In the basal region of the cell the mitochondria are oriented parallel to the long axes of the folded plasma-lemma, but in the intermediate and apical portions they are randomly scattered within the cytoplasmic matrix. Compared to the columnar cell, the goblet cell has relatively little endoplasmic reticulum. On the other hand, the plications of the plasma membrane of the goblet cell greatly exceed those of the columnar cell. One can distinguish at least four characteristic types of folding: (a) basal podocytelike extensions, (b) lateral evaginations, (c) apical microvilli, and (d) specialized cytoplasmic projections which line the goblet chamber. Apically, the projections are large and branch to form villus-like units, whereas in the major portion of the cavity each projection appears to contain an elongate mitochondrion. Junctional complexes of similar kind and position appear between neighboring columnar cells and between adjacent columnar and goblet cells as follows: a zonula adherens is found near the luminal surface and is followed by one or more zonulae occludentes. The morphological data obtained in this study and the physiological information on ion transport through the midgut epithelium have encouraged us to suggest that the goblet cell may be the principal unit of active potassium transport from the hemolymph to the lumen of the midgut. We have postulated that ion accumulation by mitochondria in close association with plicated plasma membranes may play a role in the active movement of potassium across the midgut.     

A histological and ultrastructural comparison of the male accessory reproductive glands of diapausing and non-diapausing adults in Bruchidius atrolineatus (Pic) (Coleoptera : Bruchidae)

Cytological variations of the median and the 2 lateral accessory glands of Bruchidius atrolineatus Pic (Coleoptera : Bruchidae) were examined as a function of age and the reproduction of the male. In sexually active virgin males, the secretory epithelium is columnar at emergence, but progressively flattens, and the secretions formed and stored by its cells are expelled by exocytosis into the glandular lumen. After 10 days, the male accessory glands exhibit a stage of repletion, characteristic of glands temporarily storing their secretions in their lumen. In diapausing males, the genital tract is relatively undeveloped and the accessory glands are reduced to tubules, whose lumen, surrounded by an epithelium composed of narrow cells, contains little secreted material. The presence of secretion aggregates in the secretory epithelial cells, the abundance of rough endoplasmic reticulum in them, and the release of a part of their secretions into the glandular lumen, indicate that reproductive diapause in B. atrolineatus is characterized by a decrease in the reproductive function. and not its total arrest.     

Structure of the kidney in the coelacanth Latimeria chalumnae with reference to osmoregulation

The morphology of the nephrons of the coelacanth Latimeria chalumnae was investigated by light microscopy. Each nephron is composed of a large renal corpuscle with well‐vascularized glomerulus, non‐ciliated neck segment, proximal convoluted tubule divided into distinct first and second segments, non‐ciliated intermediate segment, distal tubule, collecting tubule and collecting duct. The parietal layer of the Bowman's capsule of the renal corpuscle is composed of low cuboidal cells. The short non‐ciliated neck segment is lined by cuboidal epithelium. The first and second proximal segments display a prominent brush border and contain amorphous material in their lumen. The second proximal segment differs from the first segment in having taller columnar epithelium and a relatively narrow lumen. The intermediate segment is lined by non‐ciliated columnar epithelium and its lumen appears empty. The distal tubule is narrow in diameter and its cuboidal epithelium is devoid of intercalated cells. A unique feature of L. chalumnae is having binucleate cells in the tubule and collecting duct epithelium. The renal arteries have poorly developed tunica media and its cells contain granular material. The structure of L. chalumnae nephrons correlates well with their osmoregulatory function and resembles those of euryhaline teleosts.     

Electron microscopic study of the anterior midgut in Cenocorixa bifida Hung. (Hemiptera: Corixidae) with reference to its secretory function

The epithelium of anterior midgut of adult Cenocorixa bifida was examined with light and electron microscopy. The folded epithelium is composed of tall columnar cells extending to the lumen, differentiating dark and light cells with interdigitating apices and regenerative basal cells in the nidi surrounded by villiform ridges that penetrate deeply into the epithelium. The columnar cells display microvilli at their luminal surface. Microvilli lined intercellular spaces and basal plasma membrane infoldings are associated with mitochondria. These ultrastructural features suggest their role in absorption of electrolytes and nutrients from the midgut lumen. The columnar cells contain large oval nuclei with prominent nucleoli. Their cytoplasm is rich in rough endoplasmic reticulum, Golgi complexes and electron-dense secretory granules indicating that they are also engaged in synthesis of digestive enzymes. The presence of secretory granules in close proximity of the apical plasma membrane suggests the release of secretion is by exocytosis. The presence of degenerating cells containing secretory granules at the luminal surface and the occurance of empty vesicles and cell fragments in the lumen are consistent with the holocrine secretion of digestive enzymes. Apical extrusions of columnar cells filled with fine granular material are most likely formed in response to the lack of food in the midgut. The presence of laminated concretions in the cytoplasm is indicative of storageexcretion of surplus minerals. The peritrophic membrane is absent from the midgut of C. bifida.     

Morphological evidence for proliferative regeneration of the Anopheles stephensi midgut epithelium following Plasmodium falciparum ookinete invasion

Ookinetes are motile invasive stages of the malaria parasite that enter the midgut epithelium of the mosquito vector via an intracellular route. Ookinetes often migrate through multiple adjacent midgut epithelial cells, which subsequently undergo apoptosis/necrosis and are extruded from the midgut epithelium into the midgut lumen. Hundreds of ookinetes may simultaneously invade the midgut epithelium, causing destruction of an appreciable proportion of the total number of midgut epithelial cells. However, there is little evidence that ookinete invasion of the midgut epithelium per se is detrimental to the survival of the mosquito vector implying that efficient mechanisms exist to restore the damaged midgut epithelium following malaria parasite infection. Proliferation and differentiation of precursor stem cells could replace the midgut epithelial cells destroyed and lost as a consequence of ookinete invasion. Although the existence of so-called “regenerative” cells within the mosquito midgut epithelium has long been recognized, there has been no previously published evidence for proliferation/differentiation of these putative precursor midgut epithelial cells in mature adult female mosquitoes. In the current study, examination of Giemsa-stained histological sections from Anopheles stephensi mosquito midguts infected with the human malaria parasite Plasmodium falciparum provided morphological evidence that regenerative cells undergo division and subsequent differentiation into normal columnar midgut epithelial cells. Furthermore, the number of these putatively proliferating/differentiating regenerative cells was significantly higher in P. falciparum-infected compared to uninfected mosquitoes, and was positively correlated with both the level of malaria parasite infection and midgut epithelial cell destruction. The loss of invaded midgut epithelial cells associated with intracellular migration by ookinetes, therefore, appears to trigger, and to be compensated by, proliferative regeneration of the mosquito midgut epithelium.     

Morphological examination of immobilized Streptomyces aureofaciens during chlortetracycline fermentation

Summary Immobilized spores of Streptomyces aureofaciens ATCC 10762 were grown in situ and formed micropellets under the gel surface. The latter was covered with a membrane-like coat of alginate material, while the bead interior was almost completely free of mycelial growth.High spore concentrations caused a decrease in antibiotic production which might be correlated with the morphological development of cells in the gel.Scanning electron micrographs showed the morphological development of the immobilized cells.     

The fine structure of the digestive tubules of the Marine Bivalve Cardium edule

The epithelium lining the digestive tubules of Cardium edule consists of three cell types, namely mature digestive cells, mature secretory cells and immature flagellated cells. Both the secretory and flagellated cells exhibit a pronounced basiphilia and occur in well-defined crypts. The secretory cells are pyramidal in shape and characterized by the possession of a well-developed granular endoplasmic reticulum and Golgi apparatus. Golgi vesicles derived from the latter migrate to the apical region of the cell where they release their contents into the lumen of the tubules. It is possible that the secretion contains enzymes and although it is likely that such enzymes would function primarily in the lumen of the tubules they may also be the source of the weak proteolytic activity which has been recorded in the gastric fluid of many bivalves. The immature flagellated cells are columnar in shape and possess a poorly developed endoplasmic reticulum and numerous free ribosomes. Although no evidence for this was obtained it is suggested that they may serve to replace either or both of the mature cell types. The digestive cells vary from cuboidal to columnar, possess distinctive Golgi elements with characteristic intracisternal membranous elements, and are capable of ingesting exogenous material from the lumen of the tubule. The process of ingestion was examined following feeding experiments with (a) a mixture of iron oxide and colloidal graphite (Aquadag), (b) whole blood from pigeon and (c) ferritin. Individual particles of graphite were enclosed in phagosomes by a process of phagocytosis, while the proteins haemoglobin and ferritin were ingested by a process of pinocytosis; the membrane enclosing the pinocytic vesicles possesses a characteristic outer granular coat. The contents of both the phagocytic and pinocytic vesicles were transferred to larger bodies considered to be primarily phagosomes in the sub-apical regions of the cell. These possess an interconnecting system of membrane-bound channels which ramifies through the apical cytoplasm. Phagolysosomes deeper in the cytoplasm of the cell were identified by the presence of exogenous material and a positive reaction to tests for acid phosphatase activity. They showed changes in appearance which could be put into a series suggestive of the progressive intracellular digestion of the ingested material.     

Functional morphology of the gonoduct of the viviparous teleost Poeciliopsis gracilis (Heckel, 1848) (Poeciliidae)

Female teleosts do not develop Müllerian ducts; consequently, the ovary of teleosts contains two zones: germinal and gonoduct. The gonoduct lacks germinal cells, but has relevant functions in the reproductive process. We describe the functional morphology of the gonoduct in the viviparous teleost Poeciliopsis gracilis during nongestation and gestation stages. This study tests the hypothesis that the gonoduct functions as a barrier between the germinal zone and the exterior. By providing information about morphology and function of the gonoduct we show that this part of the ovary has an essential role in the reproduction of teleosts. The ovaries were processed by histological technique and stained with hematoxylin‐eosin (H‐E), Masson's trichrome, toluidine blue and periodic acid‐Schiff (PAS). The gonoduct is divided into three regions: cephalic, middle, and caudal. In the cephalic and middle regions there are mucosal folds that extend into the gonoductal lumen, forming structures similar to a cervix. The caudal region has two portions: the anterior contains a dorsal invagination and exocrine glands among columnar cells; the posterior has a ventral flexion and stratified epithelium with apical secretory cells. The morphology of this epithelium indicates two functions: (a) secretory by the apical columnar cells, and (b) protection through the stratification. Another peculiarity of the caudal region is that both ducts, reproductive and digestive, converge in a common cavity at their caudal ends, forming a cloacal region. The histology of the gonoduct indicates relevant functions including: (1) the control of the luminal diameter by the muscle and the presence of mucosal folds, like a cervix; (2) the relationship with the spermatozoa during insemination and storing them in mucosal folds; (3) the support of immunological processes; (4) secretory activities; (5) forming the duct during birth; and (6) possibly, acts as a barrier against parasite infestations.     

Morphological Changes in the Midgut of Aedes aegypti L. (Diptera: Culicidae) Larvae Following Exposure to an Annona coriacea (Magnoliales: Annonaceae) Extract

Bioinsecticides are important in the control of disease vectors, but data regarding their physiological effects on target insects are incomplete. This study describes morphological changes that occur in the midgut of third instar Aedes aegypti L. (Diptera: Culicidae) following treatment with a methanolic extract of Annona coriacea (Magnoliales: Annonaceae). Dissected midguts were subdivided into anterior and posterior regions and analyzed by light and scanning electron microscopy. Insects exposed to the extract displayed intense, destructive cytoplasmic vacuolization in columnar and regenerative midgut cells. The apical surfaces of columnar cells exhibited cytoplasmic protrusions oriented toward the lumen, suggesting that these cells could be involved in apocrine secretory processes and/or apoptosis. We report that A. coriacea extracts induced morphological alterations in the midgut of A. aegypti midgut larvae, supporting the use of plant extracts for control of the dengue vector.     

Ultrastructure of the endolymphatic sac in the larva of the Japanese red-bellied newt Cynops pyrrhogaster

The ultrastructure of the endolymphatic sac (ES) of the late stage larva of the Japanese red-bellied newt, Cynops pyrrhogaster (stage 57), was examined by light and transmission electron microscopy. The two endolymphatic sacs are located at the dorsal-medial side of the otic vesicle on the dorsal-lateral side of the midbrain in the cranial cavity. The wall of the sac is composed of a layer of cubical epithelial cells with loose, interposed intercellular spaces. The sac contains a large luminal cavity, in which endolymph and numerous otoconia are present. The epithelial cells of different portions of the sac have a similar structure. These cells contain an abundance of cytoplasmic organelles, including ribosomes, Golgi complexes, and numerous vesicles. Two types of vesicles are found in the epithelial cells: the “floccular” vesicle and the “granular” vesicle. The floccular vesicles are located in the supra- and lateral-nuclear cytoplasm and contain flocccular material. The granular vesicles have a fine granular substance and are usually situated apposed to the apical cell membrane. The granular vesicles are suggested to be secreted into the lumen, while the floccular vesicles are thought to be absorbed from the lumen and conveyed to the intercellular spaces by the epithelial cells. The apical surfaces of the epithelial cells bear numerous microvilli. Apparently floating cells, which bear long microvilli on the free surfaces, are observed in the lumen of the ES. Based on the fine structure, the function of the endolymphatic sac of the newt Cynops pyrrhogaster is discussed.     

The structure of the egg-shell of gLobodera rostochiensis (Nematoda: Tylenchida)

Perry R. N., Wharton D. A. and Clarke A. J. 1982. The structure of the egg-shell of Globodera rostochiensis (Nematoda: Tyienchida). International Journal for Parasitology12: 481–485. The ultrastructure and histochemistry of the egg-shell of Globodera rostochiensis are described. The eggshell consists of an outer vitelline layer, a chitinous layer and an inner lipid layer. The vitelline layer is not unit membrane-like and has strands of particulate material attached to its outer surface. The chitinous layer is made up of fibres consisting of a chitin microfibril core, surrounded by a protein coat. The lipid layer contains lipoprotein membranes. These vary in number, the most commonly observed pattern being two or three membranes loosely associated with the inner surface of the egg-shell.     

嘉庚蛸雌性生殖系统组织学观察

对象山港自然海区中的嘉庚蛸(Octopus tankahkeei)雌性生殖系统的组织学结构进行了研究.结果表明,雌性生殖系统由卵巢、输卵管、输卵管腺组成.卵巢单个、球形,内包裹滤泡细胞围成的卵子,输卵管1对,开口于外套腔中部,每条输卵管中部膨大形成圆球状的输卵管腺.近端输卵管内具两瓣蘑菇状突起,上有不规则短指状分枝,突...     

Regeneration of midgut epithelial cell in the silkworm, Bombyx mori, infected with viruses

In the larvae of the silkworm, Bombyx mori, the regeneration of midgut cells infected with a cytoplasmic polyhedrosis virus (CPV), a flacherie virus (FV), and a small DNA virus (SDV) was studied. Large numbers of newly developed cells appeared in the CPV-infected part of the midgut epithelium just before larval molt, and along with their development, the CPV-infected old columnar cells were discharged into the midgut lumen during the molt. On the other hand, in the uninfected portion of the midgut only a few cells developed, and no columnar cells were discharged. Similarly, the marked replacement of midgut epithelial cells during larval molt was also observed in larvae infected with CPV + FV. In the larvae infected with CPV + SDV, the columnar cells lost their regenerative ability, and because of the exfoliation of infected columnar cells, the midgut epithelium consisted mainly of uninfected goblet cells at a late stage of infection. The degree of epithelial regeneration varied with the silkworm strain and the dosage of the virus.     

Ultrastructural changes of the esophageal bulb of the adult female apple maggot,Rhagoletis pomonella (Walsh) (Diptera : Tephritidae)

The esophageal bulb (EB) of Rhagoletis pomonella (Walsh) (Diptera : Tephritidae) is a diverticulum which forms early in pupal development and persists through adult life. Columnar cells at the apex of the EB remain ultrastructurally undifferentiated for 1–2 weeks after the organ's first appearance. They then undergo modifications, the most prominent being the invagination of apical and apicolateral plasma membranes into leaflets, which lie in close proximity to mitochondria. Extracellular spaces defined by these membranes often become distended with electron-lucent material following the ingestion of glucose solutions. Following sexual maturity, a gradual, progressive degeneration becomes evident in the columnar cells. The cuboidal cells, which comprise the remainder of the EB, remain ultrastructurally unspecialized throughout life. The lumen of the EB is lined with an intima continuous with that of the esophagus. A fibrous mass found in the lumen may be derived from this intima. Actively dividing bacteria are found in close association with the fibers. The possible roles of the EB in the prevention of loss of beneficial gut flora and the maintenance of salt and water balance are discussed in light of the ultrastructural findings.     

Fine structural changes of Acetobacter suboxydans during growth in a defined medium

Cytological differences were observed between stationary- and exponentialphase cells of Acetobacter suboxydans grown in a defined medium. Unstained cells observed with the light microscope just after entering the stationary phase differed from exponentially growing cells in that the former exhibited localized increases in density, particularly in the polar regions. Electron microscopy of thin sections revealed that early stationary-phase cells possessed predominantly polar complexes of intracytoplasmic membranes accompanied by polar increases in ribosomal material. When cultures were allowed to continue far into the stationary phase, cells contained extensive aggregations of membrane-like material as the predominant fine-structural feature. In contrast, thin sections of exponentially growing cells exhibited only occasional indications of intracytoplasmic membranes. Intracytoplasmic membranes heretofore have been observed only rarely in the heterotrophic Pseudomonadales.     

Fine structure of the male accessory glands in Aedes triseriatus

The paired accessory glands of the male mosquito, Aedes triseriatus, consisted of a single layer of columnar epithelial cells enclosed by a richly-nucleated circular muscle layer. Each accessory gland is divided into an anterior gland (AG) with one type of secretory cell, and a posterior gland (PG) with two types. The cells of the AG and those of the anterior region of the PG showed macroapocrine secretion. The mucus secreting cells located at the posterior region of the PG, however, released their contents into the lumen of the gland by rupturing the apical membrane of the cell. The secretion from all cells was in the form of membrane-bound granules which had distinct electron-dense and electron-lucent areas.     

Morphological,ultrastructural, histochemical and electrophoretic studies on the venom system of Nasonia vitripennis walker (hymenoptera: Pteromalidae)

The venom system of Nasonia vitripennis is well-developed and composed of an unbranched acid gland and associated reservoir. Fine-structural, histochemical and electrophoretic studies indicate that the venom is produced by two protein-secreting epithelia. The bulk of the venom is synthesised in the columnar cells of the acid gland and discharged via “vesicular organelles” and the efferent ductular system into the lumen of the reservoir. The acid gland also contains squamous chitogenous cells, situated either around the central lumen or interposed between the bases of the columnar cells. Once within the reservoir, the venom is probably activated by enzymatic secretions from the reservoir secretory cells. Each of these cells has a “vesicular organelle” but, in contrast to the columnar cells of the acid gland, the cytoplasm contains a preponderance of free ribosomes, and protein segregation apparently occurs outside the Golgi complexes. The venom is expelled through the efferent discharge duct by muscular contractions, which open the duct lumen and bring it into contact with the funnel of the ovipositor. Excessive distortion of the duct is prevented by a massive ventral ligament.     

Early Development of the Secretory Cavity of Peltate Glands in Humulus lupulus L. (Cannabaceae)

Early development of the secretory cavity of chemically fixed peltate glands in Humulus lupulus L. showed secretions with different densities, light, gray and dark, in the cytoplasm of disc cells and in the periplasmic space adjacent to the developing secretory cavity. Secretions were detected in the disc cell wall and subsequently in the developing secretory cavity under the subcuticular wall of the sheath. Light and gray secretions in the cavity possessed a membrane-like surface feature. Secretions were in contact with the irregular inner surface of the cuticle. Secretions contributed to the thickening of the cuticle, whereas the membrane-like surface feature contributed to a network of Cannabis striae distributed throughout the cuticle. This study supports an early development and organization of the secretory cavity in H. lupulus, parallel to those in Cannabis, and may represent common features for lipophilic glands in angiosperms.     

野生与养殖黄鳍鲷消化道形态组织结构

采用常规石蜡组织切片的方法对野生和养殖黄鳍鲷(Sparus latus)消化道的形态组织结构进行了比较观察。结果表明,野生和养殖黄鳍鲷的消化道存在一定差异。(1)形态学研究表明,食道粗而短,胃呈V形,分为贲门部、胃体部和幽门部,胃与肠的连接处有4条幽门盲囊,肠道在体腔内迂回两个回折。野生黄鳍鲷牙齿更为坚硬锋利,体腔中脂肪较少,消化道更为粗短。野生和养殖黄鳍鲷的肠道系数分别为0.71±0.03和0.94±0.12。(2)组织学研究表明,食道黏膜上皮由扁平细胞层和杯状细胞层组成,杯状细胞发达。胃黏膜由单层柱状上皮组成,无杯状细胞,贲门部和胃体部胃腺发达。幽门盲囊组织学特征与肠相似,上皮为柱状上皮,其中的杯状细胞少于肠。肠中,前肠杯状细胞最多,中肠次之,后肠最少。直肠杯状细胞多于肠。野生与养殖黄鳍鲷组织学的区别在于,消化道相同部位养殖鱼的杯状细胞多于野生鱼,野生鱼的肌层厚度大于养殖鱼。黄鳍鲷消化道的形态组织结构与其生活环境和食物是相关的。     

Histological and ultrastructural investigation of the female reproductive system of Argulus bengalensis Ramakrishna, 1951 (Crustacea: Branchiura)

In order to understand branchiuran reproductive biology, it is imperative to know the sites of oogenesis and oocyte maturation, locate the accessory reproductive glands, and identify the fertilization site with the present knowledge of the sperm transfer mechanism of the genus Argulus. With these objectives, we attempted to describe the female reproductive system of Argulus bengalensis using serial histological sections through the ovaries and associated ducts in the transverse, longitudinal, and sagittal planes. The reproductive organs include a median ovary, one pair of ovarian lumina, a median oviduct, and a pair of collateral accessory glands. A duct from each of the collateral accessory glands leads into the proximal part of the median oviduct, which opens to the exterior through a genital opening at the distal end. The glandular secretion presumably contributes to the jelly coat of the egg. The ovary is bound with a tunica propria which extends further diametrically inside the ovary forming the paired lumina. The lumina are confluent into the median oviduct. Two distinct areas, the germarium and differentiating zones, are clearly distinguishable within the ovary. The tunica propria itself houses the oogonia within a matrix, serving as the germarium. Transmission electron micrograph reveals that the matrix is made of collagen. The collagen matrix confers elasticity to the tunica propria to accommodate the postvitellogenic oocytes within the ovarian lumen. The differentiating zone is situated in between the germarium: dorsally it is covered with a chromatophore layer. The ovary is ensheathed by a circum ovarian striated muscle. The presence of spermatophores in the ovarian lumen indicates the fertilization site. J. Morphol. 277:707–716, 2016. © 2016 Wiley Periodicals, Inc.