Three species of Macrobiotidae, Macrobiotus polonicus, Macrobiotus diversus and Macrobiotus pallarii, were selected for analysis of the fine structure of the midgut epithelium. They are gonochoric and carnivorous species that live in wet terrestrial and freshwater environments. The ultrastructure of the midgut epithelium of the investigated Macrobiotidae species was analysed in both males and females. Their digestive system is composed of fore- and hindguts that are covered by a cuticle, and the middle region, termed the midgut. It is lined with a simple epithelium that is formed by digestive cells that have a distinct brush border. Crescent-shaped cells that form an anterior ring in the border between the fore- and midgut were detected. The ultrastructure of the intestinal epithelium of the examined species differs slightly depending on sex. The digestive cells of the posterior segment of the intestine contain numerous lipid droplets, which are the reserve material. We concluded that the digestive cells of the Macrobiotidae midgut are responsible for its intracellular digestion owing to endocytosis. They also participate in the extracellular digestion owing to merocrine secretion (exocytosis). However, the midgut is not the main organ that accumulates reserve material. Additionally, the midgut epithelium does not participate in oogenesis.

中文翻译：

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三种大生物科中肠上皮的超微结构（Tardigrada：Eutardigrada：Parachela）

三种Macrobiotidae的Macrobiotus polonicus，Macrobiotus diversus和Macrobiotus pallarii选择用于分析中肠上皮的精细结构。它们是生活在潮湿的陆地和淡水环境中的食虫和食肉物种。在雄性和雌性中都分析了所研究的Macrobiotidae物种的中肠上皮的超微结构。它们的消化系统由被表皮覆盖的前肠和后肠以及称为中肠的中间区域组成。它衬有简单的上皮细胞，由具有明显刷状边界的消化细胞形成。检测到在前肠和中肠之间的边界形成前环的新月形细胞。受检物种的肠上皮超微结构根据性别而略有不同。肠后段的消化细胞含有大量脂滴，这是储备材料。我们得出的结论是，由于内吞作用，Macrobiotidae中肠的消化细胞负责其细胞内消化。它们还由于甲硫氨酸的分泌而参与细胞外消化（胞吐作用）。但是，中肠不是积累储备物质的主要器官。另外，中肠上皮不参与卵子发生。