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  • 1
    Electronic Resource
    Electronic Resource
    Ultrastructural changes in the gastrodermal phagocytic cells of the planarian Dugesia gonocephala s.l. during food digestion (Plathelminthes) (1988)
    Springer
    Zoomorphology 108 (1988), S. 109-117 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the present report the functional morphology of the planarian gastrodermal phagocytic cells is examined in feeding animals. A functional interpretation of some of the morphological findings is given. The events in the fine-structure modifications of the phagocytic cells in the course of phagocytosis and intracellular digestion of food particles were followed through five post-feeding stages in the planarian Dugesia gonocephala. Light and electron microscopical observations demonstrate that there is preliminary intraluminal digestion of food particles; their phagocytosis takes place quickly. Beef hepatocytes that served as food are found engulfed at first in food vacuoles near the apical border of the phagocytic cells, and are clearly recognizable. The vacuoles increase in number to occupy most of the cytoplasm of these cells. Progressive breakdown and disappearance of phagocytosed hepatocytes occurs. In time the vacuoles move deeper into the cells, their contents lose their identity, and condense to homogeneous or heterogeneous residual bodies. These are returned to the distal surface of the cells, and then voided into the intestinal lumen. At the same time, synthesis and accumulation of numerous lipid droplets occurs, probably as a final product resulting from metabolism of the digested material. When feeding is over, the phagocytic cells are filled with lipid droplets, acquiring their typical appearance. It is suggested that disintegration of phagocytic cells during starvation is balanced by proliferation and differentiation of neoblasts into new phagocytic cells during the feeding-starvation cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539786
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrastructural study of two glandular systems in the proboscidial glandular epithelium of Riseriellus occultus (Nemertea, Heteronemertea) (1998)
    Springer
    Zoomorphology 117 (1998), S. 247-257 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Two different types of glandular system in the proboscidial epithelium of Riseriellus occultus have been investigated by transmission electron microscopy. As expected, most of the epithelial cells are glandular in nature. With regard to differences in the ultrastructure of these gland cells and in the formation and morphology of their secretory granules, we have categorized and described four types of gland cell, indicated as G1, G2, G3, and G4. Each gland cell has a completely intraepithelial body characterized by a prominent nucleus, developed rough endoplasmic reticulum, Golgi complexes, and numerous secretory granules at different stages of maturation. These four types of gland cell appear associated in pairs forming numerous glandular systems of two types (A, B). These glandular systems are restricted to the ventral surface of the proboscis and are scattered irregularly throughout its length. Each glandular system consists of two gland cells of different types. The gland cell necks in each glandular system extend together to the epithelial surface; they protrude onto this and form a papilla where they open in a common area. The epithelial supportive cells adjacent to the glandular systems have long, stout microvilli which have a core of tonofilaments. These tonofilaments gather into dense bundles which pass vertically through the supportive cells and attach to the extracellular matrix underlaying the cells by hemidesmosomes. Moreover, a single sensory process stands close to each papilla. The ultrastructural morphology of the type A glandular systems suggests that they have an adhesive function operating in a similar way to that of the duo-gland adhesive systems in other invertebrate groups, although they are not homologous with these. The spatial arrangement of the secreted products of the type B glandular systems suggests that these may contribute to increasing the grip of the proboscis on the prey. The secretory granules (=pseudocnids) of the type G3 gland cells are very likely an autapomorphy of the Anopla, providing a character by which the relationships within the Nemertea can be evaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004350050049
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  • 3
    Electronic Resource
    Electronic Resource
    Scanning electron microscopy of adult Dicrocoelium dendriticum (1988)
    Springer
    Parasitology research 74 (1988), S. 235-242 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Scanning electron microscopy (SEM) has been used to study the tegument and related structures of adult Dicrocoelium dendriticum. Its body shape, suckers, common genital pore, Laurer's canal pore, excretory pore, and cirrus are described as seen under SEM. The tegument is devoid of spines and presents an interlacing, ridged network which covers the entire body. The pattern of ridges on the body surface is not homogeneous; details of the pattern in each region are described. SEM of the body surface reveals the high density of tegumental vesicles on ridge walls and valley floors. The tegument also bears small finger-like projections in certain areas. The authors suppose that the vesicles and finger-like projections of the tegument may well be the same structure in different functional stages. Some considerations on the significance of the tegumental differences in each body region are given. Four types of tegumental papillae occur on the suckers and body surface of D. dendriticum: button, rosette, plate, and domed. The dimensions, shapes, position, and arrangement of the papillae are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539571
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  • 4
    Electronic Resource
    Electronic Resource
    Ultrastructural study of the spermatogenesis and mature spermatozoa ofDicrocoelium dendriticum (Plathelminthes, Digenea) (1993)
    Springer
    Parasitology research 79 (1993), S. 204-212 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The spermatogenesis and spermatozoon ofDicrocoelium dendriticum were studied by transmission electron microscopy. Peripheric accessory cells project between germ cells. Each spermatogonium gives rise to 32 spermatozoa. The stages in spermiogenesis include development of the zone of differentiation, appearance of the intercentriolar body flanked by two centrioles from each of which a free axoneme and a striated rootlet grow, outgrowth of the differentiation zone to form the median cytoplasmic process and migration of the nucleus and mitochondria into it, and rotation of the flagella and subsequent proximodistal fusion of the three projections to form a monopartite spermatozoon. The spermatozoon possess two incorporated axonemes with the “9+1” pattern typical of those in trepaxonematid plathelminths. β-Glycogen particles accumulate in the spermatozoa after they have separated from the cytophore as revealed by Thiery's method. This study confirms in a further family, Dicrocoeliidae, the constant pattern of spermiogenesis and spermatozoon structure in Digenea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00931894
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    Paper (German National Licenses)
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