龟足消化系统形态和组织学特点

Morphological and Histological Characteristics of Digestive System in Capitulum mitella

应用光学显微镜观察龟足(Capitulum mitella)消化系统的形态和组织结构。龟足的消化系统包括消化腺和消化道。消化腺一对,呈长囊状,含有分泌细胞(B细胞)、吸收细胞(R细胞)、储存细胞(F细胞)和胚细胞(E细胞)4种类型细胞。消化道呈U型,由口、食道、胃、肠、直肠和肛门组成,各部分的结构由内到外可分为黏膜层、黏膜下层、肌层和外膜4层。口器为咀嚼型,包括一片上唇、一对触须、一对大颚以及两对小颚。食道细短,具几丁质层但无基膜,管壁向腔内突起形成明显的纵褶突;食道前段的环肌特别发达,同时独有放射肌。胃略呈球袋状,肠较长;胃和肠的组织结构相似,没有几丁质层,上皮细胞都有发达的微绒毛。直肠细长,外膜分布有16组纵肌;直肠前段的组织结构与胃、肠相似,而直肠后段有几丁质层覆盖,黏膜层、黏膜下层、肌层和外膜渐退化,16组纵肌渐发达。肛门16组更加发达的纵肌挤入上皮细胞下方,在外膜外另出现一层明显的环肌。龟足消化道各部分的组织结构差异明显,反映了它们功能的差异。

Morphology and histology of the digestive system of Capitulum mitella were observed by light microscopy. The results showed that the digestive system consisted of digestive gland and digestive tract. A pair of long cystic digestive glands contained four types of ceils： secretory cells, resorptive cells, inocyte cells and embryonic cells. The digestive tract consisted of mouth, esophagus, stomach, gut, rectum and anus. The mandibulate mouthpart comprised of a labrnm, two palpuses, two mandibles and four maxillas. From inner to outer, the wall of the digestive tract was divided into four layers： mucous layer, submucous layer, muscular layer and outer membrane. The wall of the thin and short oesophagus was lined with cuticle without basement membrane and possessed a layer of thick circular muscle and radiating muscle. The stomach was sacculate, and the gut was the longest in the digestive tract. Histological structure of the stomach and the gut was similar to each other. Both of them lacked cuticle, and their epithelium cells were covered with well-developed microvilli. The rectum was slender. The most obvious difference between the rectum and other parts was that 16 groups of longitudinal muscle distributed in its outer membrane. Histological structure of the anterior rectum, covered with well-developed microvilli, was similar to that of the stomach and the gut. The wall of the posterior rectum gradually degraded, but 16 groups of longitudinal muscle in its outer membrane gradually developed. The anus possessed well-developed longitudinal muscles and circular muscles which circled around outside of the anal wall. Histological structure of C. mitella in various parts of the digestive tract was different, reflecting differences in their functions.