It is known that a number of species in the annelid family Lumbricidae harbor symbiotic microorganisms in the lumen of their nephridia. The purpose of the present paper is the study of the relationship between microbes and epithelial cells lining the metanephridium of two species of Oligochaeta, which show two different patterns of microbial colonization. A new interesting feature, the phagocytosis and intracellular destruction of microorganisms by the nephridial epithelial cells, has been observed in our laboratory for the first time. In Scheroteca savignyi minor, the phagocytic activity takes place in the bladder, the most distal region of the nephridium, next to the nephridiopore, which may prevent the microorganisms from entering the more proximal regions. In Octolasion cyaneum the microbes reach the striated duct, where they live in symbiosis, adhere to the cell's surface, and are engulfed and destroyed by the cells of the middle tubule-the more proximal, neighboring region. The phagocytosis and intracellular degradation of microorganisms probably lead to the massive formation of lamellar bodies, which are observed in these cells and in the neighboring ones.

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Encapsulators are cohesive noun phrases that compress the content of discursive segments of predicative nature. Their persuasive potential has been extensively highlighted in the literature. Some studies have identified general tendencies in the use of encapsulators in thematic or rhematic positions. However, the parameters influencing the preference for thematic or rhematic encapsulators have not been specifically addressed with quantitative data. The aim of this article is to analyse those parameters in a corpus of newspaper editorials. We have selected several parameters, most of them related to their evaluative and/or persuasive potential, that might influence the use of encapsulators in the thematic-rhematic progression. Rhematic encapsulators are slightly more frequent, but we show that there are no clear correlations between each pair of parameters. Although evaluation seems to play a role (the most evaluative encapsulators tend to appear in rhematic positions), we try to show that this is mediated by many other factors that make encapsulation a less predictable type of referential expression. We also reflect on the importance of other parameters, i.e. cognitive (accessibility) and textual (genre).

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